Swimming, a sport practiced in hypogravity, has sometimes been associated with decreased bone mass.This systematic review aims to summarize and update present knowledge about the effects of swimming on bone mass, structure and metabolism in order to ascertain the effects of this sport on bone tissue.A literature search was conducted up to April 2013. A total of 64 studies focusing on swimmers bone mass, structure and metabolism met the inclusion criteria and were included in the review.It has been generally observed that swimmers present lower bone mineral density than athletes who practise high impact sports and similar values when compared to sedentary controls. However, swimmers have a higher bone turnover than controls resulting in a different structure which in turn results in higher resistance to fracture indexes. Nevertheless, swimming may become highly beneficial regarding bone mass in later stages of life.Swimming does not seem to negatively affect bone mass, although it may not be one of the best sports to be practised in order to increase this parameter, due to the hypogravity and lack of impact characteristic of this sport. Most of the studies included in this review showed similar bone mineral density values in swimmers and sedentary controls. However, swimmers present a higher bone turnover than sedentary controls that may result in a stronger structure and consequently in a stronger bone. Osteoporosis and related fractures are a considerable health concern worldwide The osteogenic effect of exercise is mainly produced by the impacts and mechanical loads applied to the bone. The modelling and remodelling bone turnover process adapts the bone to new demands and, as a consequence, bone mineral content (BMC) and density (BMD) are modified Recent literature reviews have shown that high impact sports seem to be more osteogenic than non impact sports such as swimming or cycling, in children Previous studies performed on swimmers use a variety of techniques to evaluate bone mass and bone metabolism. Dual-energy x-ray absorptiometry (DXA), as a ‘gold standard’ method for measuring bone mass, has been used to evaluate BMC and BMD. Peripheral quantitative computed tomography (pQCT) provides data regarding cortical and trabecular bone and, therefore, internal architecture, geometry and current bone strength. Another technique to evaluate bone parameters in swimmers has been quantitative ultrasound (QUS); its use in young populations is gaining rapid support because results are less likely to be affected by bone size and the technique is less expensive and invasive than other radiologic methods.The heterogeneity of the studies  makes comparisons between studies difficult; however, a systematic review and summary of the available literature on bone mass and swimmers may help to detect possible concerns and to define topics for future research. Therefore the aim of this review was to summarize current knowledge on bone characteristics in swimmers.This study followed the systematic review methodology proposed in the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement Studies were identified by searching within the electronic databases and consultation with experts in the field. This search was applied to Pubmed, Embase and SportDiscus. The search was conducted up to and including 30 April 2013.The thesaurus of the words: swimmer*, swimming , bone density, bone and bones were researched in each database. An advanced search was then carried out in which the thesaurus we had found  for the “bone terms” were combined with the Boolean operator “OR”. This resulted in a number which was subsequently combined with the number obtained from the “swimming/swimmer” thesaurus searched with the Boolean operator “AND”.Two reviewers independently examined each database to obtain the potential publications. Relevant articles were obtained in full, and assessed against the inclusion and exclusion criteria described below. Inter-reviewer disagreements were resolved by consensus. Arbitration by a third reviewer was used for unresolved disagreements.Types of study: Cross-sectional, longitudinal, randomized and non-randomized controlled trials studying the effects of swimming training programmes on bone mass with or without coexistent treatments.Types of participants: children, adolescents, adults and elderly populations.Types of intervention: trials comparing the effects of following or not following an exercise training programme and descriptive cross-sectional or longitudinal studies.Types of outcome measured: BMC and BMD of whole body, lumbar spine, arm, hip , bone architecture (from pQCT), ultrasound parameters (Broadband Ultrasound Attenuation (BUA), Speed of Sound (SOS), stiffness index) and metabolic biomarkers.1) Studies in languages other than English or Spanish 2) Unpublished data 3) Studies with animals 4) Studies without a control group that would permit comparison, and 5) Studies focusing exclusively on bone markers not measuring bone with an imaging technique.Searches identified 423 potentially relevant articles and an additional 7 articles were identified through reference lists. Following review of titles and abstracts and excluding the duplicates, the total was reduced to 154 potentially relevant papers for inclusion. Of these articles, 64 met the selection criteria and were included in this review .Studies were assessed using 2 different quality assessment tools. For cross-sectional studies we used the same quality assessment tool as Olmedillas et al. Results have been divided into two sections; The first section (3.1) organized according to the type of device used for the bone analysis, and the second section (3.2) organized according to factors affecting bone mass. Studies included in this review are summarized in Regarding the quality assessment; cross-sectional studies  were mosThe majority of the studies included in this review used photon absorptiometry to assess bone mass in swimmers; in fact 53 of the 64 studies included used this method to evaluate bone mass . Dual enNilsson et al. Of the 6 studies Only 2 studies The only longitudinal study performed in postmenopausal former swimmers showed lower BMD and BMC reductions during a one year follow-up in the former swimmers than the sedentary controls It would therefore appear that swimming may be beneficial in later adulthood. In spite of these results, out of the 7 aboved mentioned studies per se in children Lower BMD values in swimmers than other SG, were not exclusive to later adulthood. Many studies also showed lower leg BMD values in adolescent These lower BMD or BMC values in swimmers compared to SG were accompanied in a small, but still relevant number of studies Of the 50 studies that measured BMD or BMC only Courteix et al. In addition to the cross-sectional studies that revealed lower BMD or BMC in swimmers than gymnasts This is extremely important because sporting participation, specially during growth, seems to be effective in reducing the prevalence of osteoporosis-related fractures To summarize, it seems that swimming does not produce enough power to stimulate bone growth above the regular pattern, with most studies showing similar BMD or BMC values to CG Bone strength is determined by BMD and bone geometric properties A basic means of studying bone structure is by performing a radiography as Xia Qu Ma Similar results were found when bone geometry was assesed by Liang et al. Ferry et al. In summary, although swimmers may show weaker bone when compared to other weight-bearing sports as a result of smaller cross-sectional areas, the characteristics of the sport may adapt the bone to a higher trabecular CSA The use of quantitative ultrasound (QUS) is an option that avoids results biased by differences in body size among subjects. The values of SOS, BUA, and the Stiffness index (SI) derived from both of the former, provided by the QUS, are related to bone density and structure Taaffe et al. To our knowledge only one longitudinal 12 month follow-up study using QUS has been performed in swimmers We can briefly conclude that swimmers have higher QUS values than CG although these values seem to be higher in high impact sports than in swimmers. It is worth noting that the higher QUS values in swimmers when compared to CG were generally present in the lower limbs. However, the major forces applied in some swimming styles such as crawl or backstroke are applied with the upper limbs. This would suggest that the higher QUS values presented by the swimmers but not by the synchronized swimmers Bone is a metabolically active tissue that is constantly changing, with BMD being the result of bone formation and resorption which are closely linked in time and space within the bone multicellular unit Regarding bone formation markers, several studies showed higher bone-specific alkaline phosphatase (B-ALP) values in swimmers than in CG The use of two bone markers to evaluate bone formation Regarding bone resorption, Cross-linked N-telopeptides of type I collagen (NTx) was the most used biomarker The Osteoprotegerin(OPG)/Rank-ligand (RANKL) system which is known to have considerable influence on bone formation and degradation, has only been evaluated in one study Summarizing all the previous studies that include swimmers and bone metabolic markers we can conclude that swimming seems to involve a high bone turnover It is well known that hormone concentrations change during growth and vary during or after the practice of exerciseLima et al. Estradiol levels were also studied, with no differences found between young swimmers, CG and other sports Jürimae et al. focused on the influence of Ghrelin (GR) on BMD, showing that GR appeared to be an important hormonal predictor for BMD in swimmers Jürimae et al. IGF-I which stimulates endochondral bone formation and activates bone turnover We can therefore conclude that the values of the majority of the hormones studied were similar in swimmers and CG. However, the concentrations of some of these hormones may vary according to training loads, making the measuring period critical regarding hormone concentrations and associated effects.Most of the studies that registered calcium intake showed no differences among groups. Eigth studies showed significantly higher calcium intake values in swimmers than in CG Research has demonstrated that calcium supplementation increases bone mass significantly during childhood and adolescence Gender differences in peak bone mass acquisition are well documented in humans It seems that results in studies with either male or female participants are similar. Some studies included both genders showing no differences between groups We have observed that swimming does not seem to negatively affect bone mass and might provide a stronger bone structure than that of the CG, but weaker than that of other impact sports independently of the age group studied: children, adolescents or adults. However, as previously stated, it seems that swimming might be more beneficial later in life. Of the 5 studies performed with DXA that found benefits of swimming compared to CG, 4 were performed in adults over 40 years old, suggesting that swimming may be a beneficial activity to practice in later adulthood in order to maintain bone. It is possible that these higher bone mass values in this older population were due to a more active life than their CG, as found in some studies The number of years practiced and weekly hours trained could influence bone in different ways. Unfortunately, this information is not available in all the articles included in this review. Weekly training hours were therefore evaluated when specified by the authors and no evidence of its influence on bone mass was found, in fact, the data presented in each article regarding weekly training hours and years of practice were not clearly specified and therefore cannot be taken into consideration. Training intensity may also differ between groups that perform the same sport modality and train for a similar number of hours. Different intensities can result in different sport performances and also in different body composition and bone adaptations. Magkos et al. In addition to swimming hours, many swimmers also perform strength training that could also affect bone. This type of training was generally not reported in most of the studies included in this review. However, due to the osteogenic effect that this type of training has, it is important that future studies evaluating bone in swimmers take this parameter into accountThe current systematic review excluded non-English and non-Spanish publications; therefore a possible language bias appears. The included studies were too heterogeneous to perform a meta-analysis. The lack of this type of analysis makes it difficult to obtain strong conclusions. Although Although few studies found lower BMD in swimmers when compared to sedentary controls most of the research shows similar BMD for both groups independently of the age group, except for later adulthood where swimmers presented lower bone mass decrease than sedentary controls, although it is not clear if these differences are sport-specific or are due to the more active life-style reported in swimmers. It would therefore appear that swimming does not negatively affect bone mass. Swimmers mostly showed lower BMD values than any other SG independently of the age of the sample. In fact, longitudinal studies showed lower BMD increases during a season in this specific sport-group. Nevertheless, swimmers showed higher bone turnover values than sedentary controls that were not reflected in higher BMD. This higher bone turnover seems to be associated with a more efficient bone structure of swimmers which appears to be weaker when compared with high impact sports and stronger when compared to sedentary controls, independently of the method of analysis. Many factors may interfere in the effect of swimming on bone, although no differences among groups were found in some of them such as hormone concentrations or calcium intake, the influence as confounders of these factors has not been elucidated.There are 3 relevant remaining questions:How many hours per week, years of practice and intensity of training are needed in order to obtain this structure?Is it possible to obtain this improved structure at any stage of life, or is it only possible during childhood and/or adolescence?How long does this structure perdure without activity?Future research is needed to ascertain some of these questions and establish structural benefits of swimming on bone tissue. It is also noteworty that swimming presents lower risks of traumatic fracture than other high impact sports, it is beneficial for cardiovascular fitness Evaluation method should include:Imaging techniques: Two techniques should be employed in each study. DXA is essential and a second method of the researchers choice to evaluate bone structure, preferebly pQCT or MRI.Bone metabolic markers: To evaluate metabolic activity and view bone remodeling process.Physical activity registerAccelerometry: In order to evaluate physical activity objectively.Questionnaires: To evaluate past and current physical activity. This might be of extreme importance in studies performed in adults or elderly population.DietTo evaluate calcium, phosphorus and vitamin D intake in addition to total energy intake and other nutrients that might affect bone and body composition is of crucial importance.Other confoundersType of swimming: It is important to distinguish, if possible, between sprint swimmers and long distance swimmers due to the fact that they might present different types of training routines and these might involve different types of efforts that might affect bone in a different way.Years of practice, and weekly hours trained: Particularly when performing a study that compares sport disciplines.Complementary weight work: Many swimmers perform weight training in order to improve their performances. This should also be registered and taken into account in future studies.Point of the season: Training loads change according to the season period and this might affect bone that is constantly adapting. When performing studies that compare sports, evaluation should take place in similar load pattern periods of the different sports.Tanner stage: When performing studies with children or adolescents, tanner stage should always be registered as differences in bone might be partly due to maturation status.Menstrual status: This is another important variable to take into account due to the close relation that it has with bone.Future studies in this area should take into consideration the following aspects:Table S1PRISMA Checklist.(DOC)Click here for additional data file.Table S2Quality assessment tool of the cross-sectional included studies.(DOCX)Click here for additional data file.Table S3Quality assessment tool of the included longitudinal studies.(DOCX)Click here for additional data file.


Shigella, a bacteria that kills over one million people worldwide every year. The long-term goal of this novel approach is to inform Shigella vaccine design by elucidating which immune components and bacterial targets are crucial for establishing Shigella immunity. Our delay differential equation model focuses on antibody and B cell responses directed against antigens like lipopolysaccharide in Shigella’s outer membrane. We find that antibody-based vaccines targeting only surface antigens cannot elicit sufficient immunity for protection. Additional boosting prior to infection would require a four-orders-of-magnitude increase in antibodies to sufficiently prevent epithelial invasion. However, boosting anti-LPS B memory can confer protection, which suggests these cells may correlate with immunity. We see that IgA antibodies are slightly more effective per molecule than IgG, but more total IgA is required due to spatial functionality. An extension of the model reveals that targeting both LPS and epithelial entry proteins is a promising avenue to advance vaccine development. This paper underscores the importance of multifaceted immune targeting in creating an effective Shigella vaccine. It introduces mathematical models to the Shigella vaccine development effort and lays a foundation for joint theoretical/experimental/clinical approaches to Shigella vaccine design.We establish a mathematical framework for studying immune interactions with  Shigella, a bacterium that causes roughly 120 million dysentery infections and kills over 1.1 million people (predominantly young children) worldwide every year Shigella despite decades of clinical trials Shigella infections. One major hurdle in vaccine development is that identifying immunological correlates of protection in Shigella infections, whether mechanistic or nonmechanistic Vaccines protect millions of people from viral and bacterial infections every year Shigella, which we use to determine which immune effector mechanisms best confer immunity against Shigella. We concentrate our efforts on the humoral immune response, as current vaccines strive to incite protective immunity by eliciting specific memory B cells  and BShigella lipopolysaccharide (LPS) have been shown to correlate with protection Activated Shigella infections is largely unknown. Elevated levels of IFN-Shigella infections Shigella clearance is not known The role of cell-mediated immunity (CMI) in protection from Shigella must be multifaceted to clear an infection that is both intracellular and extracellular. It is likely that in the clearance of a pathogen such as Shigella, antibody responses may be important in the extracellular phase while CMI may play a dominant role in the intracellular phase. An antibody-based vaccine must not only eliminate the bacteria from the gut lumen and lamina propria but should also prevent Shigella from entering epithelial cells. Clearance of infected epithelial cells requires a CMI response. Thus, common vaccine targets include lipopolysaccharide (LPS) on the bacterial surface as well as components of the bacteria’s type III secretion system, such as IpaB and MxiH, which are critical components of the Shigella machinery that allows their entry to epithelial cells Overall, the immune response against Shigella in order to better qualitatively and quantitatively determine the effector immune responses that correlate with protection. We capture the primary immunological and bacterial dynamics with systems of ordinary and delay differential equations. Delays are employed to incorporate biological time-scale differences between existing immunity and new immune activation. Thus, in the first few days of an infection, immune protection against Shigella is conferred by innate immune cells or existing antibodies elicited by prior infections or vaccines; later, the presence of Shigella antigens elicit robust B and/or T cell responses.To this end, we develop mathematical models of the immune response against Shigella. Furthermore, while other mathematical studies have examined the impact of vaccines on pathogen dynamics , ASC, and BShigella is subject to phagocytic killing but escapes antibody action. Notably, our model does not include cell-mediated immunity components such a CTLs that might eradicate Shigella bacteria inside host epithelial cells, as T cell activity against Shigella remains largely undefined. Using the model, we examine infection dynamics both in the presence and absence of an assumed Shigella vaccine directed against Shigella outer membrane components, such as lipopolysaccharide (LPS), that are displayed throughout an infection. We investigate whether LPS-directed antibodies are sufficient to prevent a severe Shigella infection. The model incorporates both mucosal (IgA) and systemic (IgG) immune responses, and we compare which is most effective. We also focus in on Shigella’s ability to infect host epithelial cells and ask if antibodies directed against epithelial entry are necessary components of a successful Shigella vaccine.We focus on Shigella immunity. Finally, we summarize our results and discuss their implications on the Shigella vaccine development process.The structure of this paper is as follows: we first derive the model and explain the underlying biological dynamics that it captures. In the Analysis section, we identify the equilibria, including disease-free and vaccinated states, and evaluate their stability. In the Dynamics section, we present numerical simulations of the model to determine immune and bacterial dynamics before and after vaccination, to quantify the number of anti-LPS antibodies required for immune protection, and to explore the potential effectiveness of epithelial entry targeting. In the Parameters section, we alternately vary certain parameters to deduce their impact on model results  and we identify key factors that potentially correlate with Shigella’s immunological correlates of protection by developing mathematical models of the immune response against Shigella. Model results improve our understanding of the immune response elicited against Shigella, suggest alternative approaches to future vaccine design, and take the first steps in forecasting the success of their implementation.In the broader sense, this paper lays the foundation for determining Shigella once they have invaded host epithelial cells, macrophages, and other cells, since a role for this effector CMI activity in fighting infection remains to be well characterized We write a system of differential equations to capture bacterial and immune dynamics and focus on humoral immune components that can potentially be elicited through vaccination. Bacterial pathogenesis and the reaction diagram corresponding to the model are given in Shigella infection to the initialization of a new immune response; in this time window, only previously established antibodies and B cell dynamics can target the bacterial population.In our model, we incorporate delays into mathematical terms for the creation of new BShigella-specific IgA and IgG BShigella takes advantage of a natural activity of host M cells, which shuttle material from the lumen across the epithelium to innate immune cells such as macrophages that wait in the lamina propria to engulf Shigella and destroy it. Shigella travels from the lumen, where it is denoted Shigella can avoid destruction and proliferate at rate Shigella is safe from antibody targeting, and then escape back out into the lamina propria  but rather assume epithelial stress correlates with significant epithelial invasion and hence high values for Shigella proliferating before entering the lamina propria in order to avoid mathematically establishing a luminal Shigella population that persistently spawns new infections.Once within the epithelium, The equations governing the bacterial dynamics are as follows:Shigella death due to macrophage activity or other causes; Shigella removal via antibody is modeled separately. Shigella outer membrane components such as LPS, which is constantly displayed and available for antibody targeting whenever Shigella resides in the lamina propria or lumen. When sufficient numbers  A Shigella infection is cleared unless the disease is so acutely severe that it kills the host; however, a BShigella bacteria in any spatial compartment. Three disease-free equilibria exist for the model: one with mucosal (IgA-type) but not systemic (IgG-type) immunity, one with systemic but not mucosal immunity, and a joint equilibrium with both. The values of the model variables at equilibrium are given in Equilibrium analysis elucidates model dynamics between infections. Prior to a primary Shigella infection is never persistent nor chronically latent. If, however, macrophage re-engulfment of Shigella in the lamina propria is allowed–that is, if Shigella infection and prevents bacterial clearance (not shown). This chronic state is not observed biologically; hence, macrophage re-engulfment is not allowed in the model and the Shigella populations in the lamina propria are separate.Importantly, there is no completely nontrivial equilibrium of the model, which is consistent with the fact that a Shigella populations are zero at all equilibria, we examine the stability of the reduced system with Stability of the trivial and disease-free equilibria can be determined by examining the eigenvalues of the Jacobian matrix for our system of differential equations at the equilibria. Since there is no truly nontrivial equilibrium and hence the If the following two stability conditions are satisfied, the eigenvalues are all negative and hence the corresponding equilibrium is stable:For our parameters, this means that stability occurs exactly when both Shigella infection, the trivial equilibrium is not maintained and some level of permanent immunity is established. If only A-type or G-type immunity is generated initially, another infection could boost the system to the stable joint disease-free immune state. Whether these immune levels are sufficient to confer protective immunity to the host remains to be determined. Nevertheless, the model supports the hypothesis that a vaccine, which perturbs the immune system away from the trivial equilibrium, will establish a persistent nontrivial level of humoral immunity specific for Shigella.Thus, following a primary Shigella infection that occurs either prior to or months after the administration of a vaccine; the action of the vaccine mathematically is to shift the system from the trivial equilibrium to a disease-free equilibrium. Therefore, a primary Shigella infection initializes with trivial variable values while a post-vaccine Shigella infection starts at a disease-free equilibrium.  Parameter values are given in We assess the behavior of the mathematical model via numerical simulations. Using a delay differential equation solver in MATLAB, we examine the bacterial and immune dynamics during a Shigella is ingested to introduce a population of 1,000 bacteria into the gut lumen. Since a minimum of 100–1000 Shigella bacteria clinically cause disease, this is sufficient to cause infection Shigella grows and migrates unfettered in the host during the incubation period before sufficient numbers of naive B cells have been stimulated to create ASC and BShigella infection to below one bacterium in the lumen and lamina propria in 20 days, but bacteria that enter epithelial cells escape humoral immune targeting and grow without restraint. It should be noted that Shigella’s infection of the epithelium may be controlled by cytotoxic T cells and thus in reality this epithelial population would be more controlled; however, T cell activity against Shigella remains largely undefined; thus we have not included them in the model. As a result, true Shigella dynamics in response to both humoral and cell-mediated immune responses are outside the purview of this model. For our purposes, the essential fact shown by the primary infection model is that Shigella can survive well in the epithelium and thus a vaccine that effectively protects against shigellosis must prevent most epithelial entry.We establish an infection by assuming enough Shigella bacteria are introduced to the gut. The dynamics of this secondary Shigella infection are depicted in Shigella peaks.  Also noteworthy are the slowed dynamics of the epithelial cell infection, which suggests the host may experience temporarily reduced symptoms resulting from epithelial destruction. Nevertheless, the vaccine does not fully prevent the epithelial infection, which means the host must instead hope that a primary cytotoxic T cell response can clear it.Secondary immune responses are elicited when a vaccine is given that elicits LPS-directed IgA and IgG humoral immune responses and shifts the immune system to the joint disease-free equilibrium. After the host system re-equilibrates, 1,000 wild-type Shigella’s infection of epithelial cells could be prevented purely by anti-LPS antibodies if they were available in larger supply  will be sufficient to clear the infection. In fact, recent publications have begun to show that CMI responses are important. For example, the clearance of a primary Shigella infection is impaired in the absence of T cells. Additional studies demonstrated that following reinfection, IL-17A and IL-22 producing T cells are primed by Shigella and the IL-17A produced by these cells restricts bacterial growth Shigella vaccines We next ask if r supply . Here, wShigella that can infect the epithelium without the host becoming severely symptomatic; as this value is unknown, we vary the peak number of bacteria allowed and examine the corresponding antibody requirements , lamina propria (LP), epithelium (E) or engulfed in innate immune cells (I). In Shigella peak times, which also are independent of this parameter. However, we also plot the time at which the total Shigella population in the lumen, lamina propria, and engulfed in innate cells drops below one bacterium, corresponding to Shigella extinction in non-epithelial compartments. This extinction time does increase with antibody death rates, likely because the amount of antibody capable of removing bacteria decreases.Antibody half-lives have been measured clinically in humans Shigella in the lumen and lamina propria  for IgA- and IgG-BShigella-directed BShigella present in the epithelium  consistent with what we have seen previously, the minor increase in the time to the antibody peak is sufficient to create more antibodies, despite a lower plasma cell creation rate or (2) antigenic stimulation of B cell generation due to higher Shigella levels increases sufficiently to compensate for lower BShigella drops only slightly when plasma cells are generated more quickly from BTo explore how antigen-stimulated plasma cell creation affects bacterial and immune dynamics, we look more closely at the rates that BShigella numbers decay substantially when more plasma cells are made per BShigella drops substantially when more plasma cells are generated per BShigella clearance. Furthermore, if more than When we examine how the number of plasma cells made per differentiating Br B cell . In thesed per B ; this subacteria . This asShigella and antibody dynamics are completely insensitive to changes of creation rates from naive B cells since pre-existing immunity contributions dominate (not shown). Thus, we also evaluate primary infection behavior. The faster that plasma cells are created from naive B cells, the higher the antibody peak and the more swiftly it is reached during a primary infection  the time delay  directed against specific antigens such as LPS in Shigella bacteria in the epithelium 45 days later. A primary CMI response (not modeled) in concert with a post-vaccine humoral immune response should eliminate some small amount of epithelial cell invasion, although this threshold value is unknown. However, we find that a four-orders-of-magnitude boost in IgA and IgG numbers above vaccine levels is necessary to contain the epithelial infection below a threshold of 100 bacteria, a low estimate of the minimum infectious dose in humans Shigella inside the epithelium and thus is likely an underestimate of antibody requirements. Therefore, it will be difficult to elicit sufficient numbers of antibodies targeting only Shigella LPS (or other outer membrane components) to prevent shigellosis.To explore whether a larger amount of anti-LPS antibodies than a vaccine elicits can prevent disease, we boosted IgA and/or IgG antibody numbers prior to infection via initial conditions and tracked the number of Shigella vaccine can sufficiently boost not only anti-LPS antibodies but anti-LPS BShigella. However, more careful sensitivity analysis will be required to ensure that BThe caveat is that if a Shigella at the outset before it has the opportunity to proliferate. However, more total IgA is required than IgG to have an equal effect, because only IgA antibodies that reach the lumen contribute to this higher-per-molecule defense. A combined strategy with both IgA and IgG responses requires less total antibodies than IgA alone or IgG alone and thus is predicted to confer the best protection.While varying the initial IgA and/or IgG levels to determine the impact of antibody boosting, we are able to determine the relative effectiveness of IgA antibodies versus IgG antibodies. Although their efficacies are closely matched, the modeling results tell us that each IgA antibody is slightly more effective than an IgG antibody. Since the model’s IgA and IgG parameter values are identical, this likely results from the fact that IgA functions in the lumen and thus eliminates Shigella epithelial entry proteins. We find that if IgG modulates the rate at which Shigella enters epithelial cells, epithelial invasion is almost entirely blocked. Thus, this vaccine strategy shows promise, yet a detailed, mechanistic model of epithelial entry that takes into account factors such as the brief availability of epithelial entry proteins is needed to better explore this avenue mathematically.Since an anti-LPS antibody response is not sufficient for immunity, we extend the model non-mechanistically to explore the potential of additionally targeting Shigella proteins involved in host cell invasion have long been considered potential vaccine targets. In fact, past vaccine trials have targeted both LPS and invasion plasmid antigens , which play a key role in epithelial entry Shigella immune interactions in the future to better inform Shigella vaccine design.Challenges exist in incorporating clinical data into the mathematical model. Human data are sparse in time and indirectly measured due to limited access to internal tissues, including the gastrointestinal mucosa. In addition, cut-offs for morbidity in patients are not quantitatively known, and thus it is not straight-forward to determine what bacterial loads and immune levels must be reached to achieve protection.Our mathematical model includes many parameters that are biologically unknown see . Our senShigella infections. The model highlights the relative importance of the efficiency of IgA versus IgG, BShigella antigens, and continued testing of the model as additional clinical data become available will accelerate the development of vaccines against Shigella.In summary, the mathematical model presented here explores several immune variables currently considered important in protection from


Standard virulence evolution theory assumes that virulence factors are maintained because they aid parasitic exploitation, increasing growth within and/or transmission between hosts. An increasing number of studies now demonstrate that many opportunistic pathogens (OPs) do not conform to these assumptions, with virulence factors maintained instead because of advantages in non-parasitic contexts. Here we review virulence evolution theory in the context of OPs and highlight the importance of incorporating environments outside a focal virulence site. We illustrate that virulence selection is constrained by correlations between these external and focal settings and pinpoint drivers of key environmental correlations, with a focus on generalist strategies and phenotypic plasticity. We end with a summary of key theoretical and empirical challenges to be met for a fuller understanding of OPs. The study of infectious diseases has become a major focus within evolutionary biology; however, remarkably little attention has been paid to an extremely broad class of pathogens, the opportunists. This oversight stems from the theoretical convenience of treating host–parasite interactions as closed systems in which a single, obligate pathogen specialises on a single host Streptococcus pneumoniae and Staphylococcus aureus) or from environmentally acquired microbes . Many more pathogens are recognised as opportunists in the sense that although they regularly cause disease in healthy humans, they are also zoonotic and exploit numerous other hosts .Opportunistic pathogens (OPs) are typically characterised in the medical literature as organisms that can become pathogenic following a perturbation to their host . These opportunists can emerge from among the ranks of normally commensal symbionts  of virulence evolution theory fail, we have an OP. In Salmonella enterica among humans living in dense and unsanitary conditions). In these cases, standard predictions from virulence evolution theory may still apply, such as a trade-off between transmission and virulence Given the failure of the two key assumptions of classical virulence evolution theory , what caIf we can understand microbial plasticity and generalism, we can understand why opportunistic bugs become pathogens, when they are likely to do this and how we can interfere with their plastic responses to control their virulence in a sustainable manner. In this review, we aim to develop a general and integrative framework for the understanding and management  of opportunistic pathogens.For population biologists, virulence is typically the increase in host mortality resulting from parasite infection VFs can be mechanistically complex and therefore are presumably products of natural selection. However, the nature of selection for maintaining and strengthening VFs remains controversial. Levin and Svanborg Edén made an important distinction between direct and coincidental selection for VFs By contrast, purely coincidental selection argues that VF expression is not positively correlated with any measure of parasitic success within the focal host; in other words, there are no benefits in the parasitic context. VFs are then fascinating spandrels P. aeurignosa and the circulatory system for S. pneumoniae) and environments where they do not . This compartmentalisation can be within a focal host  or between a focal host and another environment . To conceptualise this split, we divide the world of a microbe into two compartments: the virulence compartment V, the sensitive parts of a focal host where microbial VFs result in disease symptoms; and the asymptomatic compartment A, which is everywhere else it can grow . If, for example, both coincidental and within-host selection favour VF expression, then there is a positive environmental correlation between growth in environment A and that in environment V , and increasing evidence points to the evolution of resistance to protist predation pre-adapting certain environmental microbes for survival and even proliferation within human macrophages S. pneumoniae are pneumonia, otitis media and sepsis, and these are not contagious conditions and therefore represent a dead end, especially when the result is rapid demise of the host et al. demonstrate that capsule selection is driven in the nasopharynx by competitive interactions with another commensal, Haemophillus influenzaeH. influenzae, the capsule offers a survival advantage by reducing susceptibility to this suppression. These results also present an important reminder that OPs will often face many distinct non-virulent environments , such as environments with or without a key predator or competitor .Other potential examples of pre-adaptation include selection for capsule carriage (a VF increasing the risk of invasive disease) among pneumococcal strains in the nasopharynx et al. illustrate that growth in a crowded, immunogenic nasopharynx selects for serum resistance, which then pre-adapts S. pneumoniae for growth in blood Lysenko C. botulinum is a candidate here). However, if bacteria frequently encounter environments across which the costs of the trade-off are felt (and if sufficient genetic variation exists), then something is likely to give: evolution in the face of an important trade-off can lead to a loss of the trade-off (if the underlying constraint is weak), specialisation or plasticity.The examples above describe cases in which selection for VFs may have occurred in a setting outside of infection, but incidentally provides some benefit in terms of transmission or within-host growth . Alternaet al. posed the question as to whether generalists or specialists would be better able to exploit an entirely novel host type, previously unseen by either line A common motor of bacterial specialisation is horizontal gene transfer and loss; plasmids and phages shuttle an array of genes conferring local adaptations to heterogeneous environments Plasticity is the ability of an organism to change its phenotype without corresponding changes in genotype. Mechanisms such as altering gene expression can allow an organism to display different phenotypes in different environments Helicobacter pylori to 24 in the generalist P. aeruginosaBacterial VFs are by definition ‘optional extras’ and are often under regulatory control and are not always on, with expression responsive to both physical  and social  environmental dimensions P. aeruginosa. On initial colonisation of a mammalian host, P. aeruginosa upregulates an array of VFs Although the direct costs and benefits of a complex regulatory machinery are readily appreciated, there is also potential for indirect costs of making ‘bad decisions’ , as hintP. aeruginosa toxin pyocyanin, expression of which is driven by exposure to N-acetylglucosamine and its polymer peptidoglycan, commonly shed by Gram-positive bacteria N-acetylglucosamine-dependent pyocyanin expression is an antimicrobial mechanism in environments rich in competitors N-acetylglucosamine. There are also many well-studied examples of global regulation in quorum-sensing and stress responses (like RpoS in many proteobacteria) that strongly impact virulence The causes of some aspects of this decision-making have been brought into closer focus for the Finally, we turn to the implications of opportunism for parasite control. If most human pathogens are largely shaped by selective pressures outside of disease-causing compartments, then why is antibiotic resistance such a clear and growing problem? A major part of the answer is that for many VFs discussed above, antibiotic resistance genes can confer advantages outside of the context of human medical interventions via resistance to bacterially derived antimicrobial compounds. Consistent with this broader functionality, resistance to a range of antibiotics have been found in ancient DNA from 30 000-year-old permafrost sediments For commensal opportunists, exposure to antibiotics is routine because of their specialisation on human hosts, and therefore the emergence of antibiotic resistance in these species poses little puzzle. By contrast, non-specialists may encounter humans merely as a dynamical ‘sink’ Interest is now growing in the use of antivirulence drugs that directly target the expression of virulence factors Although there is a broad range of conceptual models for the evolution of virulence , Box 1, Our formal treatment was presented in the context of distinct physical environments ; however, the control of bacterial VF expression in response to contrasting social conditions highlights an even greater complexity and a key theoretical challenge. For instance, many bacteria can discriminate between low- and high-density environments, and even clonal versus polymicrobial conditions, via quorum-sensing mechanisms


The aim of this qualitative study was to improve the understanding of the interface between health and educational sectors. Parents of adolescents with anorexia nervosa , cancer (n=11) and cystic fibrosis  were recruited through two tertiary hospitals in Victoria. Audio-recorded in-depth interviews were conducted and transcribed verbatim. Consistent themes emerged across the three cohorts, with parents agreeing that schools needed to know of a diagnosis for health safety, academic support and positive peer relationships. However there were significant condition-specific differences. Only parents of adolescents with AN engaged in misdirection (providing a different diagnostic label) or secrecy; a significant number elected not to disclose the AN diagnosis to schools in response to their child's request. In contrast, parents of adolescents with CF who reported that their children did not wish schools to know of the diagnosis when secondary school commenced overruled such requests. Diagnosis disclosure did not emerge as an issue for adolescents with cancer; all parents promptly informed the school of the diagnosis. In summary, parents articulated consistent reasons across disease cohorts for sharing the diagnosis of a chronic health condition with schools, yet experienced different challenges in implementing this, with implications around health safety, academic support and peer relationships.


Neurons in the mammalian brain are a highly diverse population with a complex assortment of electrophysiological, morphological and molecular properties, which has hindered efforts to classify them into genetically and functionally meaningful subtypes and to understand their various roles in the normal or pathological brain. Nowhere is this issue more acutely felt than in the study of inhibitory cortical interneurons, whose classification is still a source of contention and confusion , we sectioned fixed brains from four SOM-RFP mice and dually immunostained them against PV and SOM. Two brains were from third postnatal week pups (the age range used in our recording experiments), and two were from ~1 month old animals. We imaged sections representing five cortical areas  on a confocal microscope and counted RFP+, PV+, and RFP+/PV+ double-labeled cells in confocal stacks, verifying that double labeled cells were indeed so in single optical sections Figures . In totaOur observation of RFP expression in FS interneurons cannot be explained by leaky expression of the RFP gene  or by non-specific expression of the Cre gene , because we would then expect to see widespread RFP expression in excitatory neurons, which are the majority cortical cell type. Thus, RFP expression must be under the same genetic control as the endogenous SOM gene; however, we found no SOM expression in the subset of double-labeled RFP+/PV+ neurons, consistent with previous studies which observed no overlap between SOM and PV protein expression in mouse and rat cortical interneurons (Gonchar and Burkhalter, The two alternative mechanisms above imply slightly different risks to investigators: the first implies that recombination in FS interneurons is expected when breeding SOM-Cre mice with Cre reporter lines, but not necessarily when transfecting adult neurons with viral vectors, while the second mechanism would result in off-target recombination regardless of the mode of delivery of the reporter construct. Either way, our findings underscore an important caveat for researchers using “subtype specific” mouse driver lines, including those in which the Cre coding sequence is presumed to be under the control of the endogenous gene promoter—these lines should be used with caution and with proper validation. Most studies using the SOM-Cre line appear to use it without validation; an exception is a recent study that tested recombination specificity and found that 5% of recombined neurons in the visual cortex were immunopositive for PV (Pfeffer et al.,


Progressive aging induces several structural and functional alterations in the cardiovascular system, among whom particularly important are a reduced number of myocardial cells and increased interstitial collagen fibers, which result in impaired left ventricular diastolic function. Even in the absence of cardiovascular disease, aging is strongly associated to a age-related reduced maximal aerobic capacity. This is due to a variety of physiological changes both at central and at peripheral level. Physical activity (PA) appears in general to have a positive effect on several health outcomes in the elderly. This review aims to illustrate the beneficial effects of exercise on the physiologic decline of cardiovascular performance occurring with age. Furthermore, it will be stressed also the positive effect of physical activity in elderly patients affected by cardiovascular diseases, such as heart failure and hypertension, and multiple comorbidities which may significantly worse prognosis in this high risk population. Aging induces several structural and functional alterations in the cardiovascular system  appears in general to have a positive effect on several health outcomes in the elderly: several epidemiologic studies have shown that the increase in the level of physical activities is associated to improved health outcomes  exercise programs in healthy elderly can have multiple beneficial effects on several health outcome, including a reduction in the decline in cardiovascular performance associated with physiologic aging, an improvement in physical function  or O2 , a parameter expressing the sympatho-vagal balance  due mainly to increase in stroke volume, without changes in peripheral artero-venous (A-V) O2 difference. In old healthy subjects, it has been demonstrated that physical training ameliorates age-related deterioration of cardiac function in terms of enhanced left ventricular inotropic response to catecholamines  protein and mRNA, an oxidative MHC I phenotype which is beneficial for a more efficient O2 after endurance training in healthy elderly men appears primarily due to an augmented peak stroke volume and CO and to a lesser extent to increased A-VO2 Difference. In contrast, the exercise training- induced increased peak VO2 in healthy elderly women is due entirely to an increase in peak A-VO2, with no changes in stroke volume, HR, and CO after training  is capable to improve lean tissue mass, muscle strength and several physical performance measures such as time up and go, stair-climbing power, aerobic capacity, gait speed and 6 min walking distance, which are all consequences of increased muscle mass or strength .In HFREF patients, favorable changes in exercise capacity with aerobic exercise training have been observed in elderly patients. This is particularly important since, in subjects with heart failure, exercise capacity  and other parameters obtained at a maximal cardiopulmonary exercise test. Several studies performed in HFREF patients (independently from age) have shown that endurance training induces a significant increase in peak VO2 of about 20–25%, which is correlated to survival and is one of the main prognostic indicators in HFREF  in HFREF patients, an important role is played by an increased ventilator drive through reduced lactate production at submaximal exercise level and an enhanced muscle ergoreflexes secondary to skeletal muscle myopathy  has shown some favorable effects in patients with HFREF, but the effect on cardiovascular performance is modest compared to that obtained with aerobic ET , or Respiratory exchange ratio, with reduction at submaximal exercise of arterial pressure and HR, indirect indicators of a reduced myocardial O2 consumption  and 75–80% MHR (intense exercise). If HR cannot be adopted to establish the training workload, subjective perceived exertion fatigue on a 20 points Borg scale can be utilized, trying not to increase this value above 12. All sessions should be preceded by a 5–10 min of warm-up and be followed by a period of 5–10 min of recovery. In the elderly patient training is usually started at a lower workload due to the limited baseline functional capacity and to the frequently associated comorbidities negatively influencing the physical performance. In very compromised frail elderly a high intensity exercise training may induce musculo-skeletal damage or cardiovascular complications  or to the HR achieved at a symptom limited exercise stress test or to peak VOParticularly in elderly patients with functional compromise Borg scale may be indicated to maintain the intensity of training within safe limits, provided the patients is reliable to report his symptoms during exercise. The more the elderly patients is frail or sarcopenic, the higher is the potential benefit for cardiovascular performance to include also muscle strengthening, flexibility, or balance exercise. Particularly resistance exercise, can also be useful in the elderly to improve cardiovascular performance, if adopted in conjunction with aerobic exercise training  there has been no conflict of interest during the review and handling of this manuscript. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


To truly appreciate the myriad of events which relate synaptic function and vesicle dynamics, simulations should be done in a spatially realistic environment. This holds true in particular in order to explain as well the rather astonishing motor patterns which we observed within in vivo recordings which underlie peristaltic contractionsas well as the shape of the EPSPs at different forms of long-term stimulation, presented both here, at a well characterized synapse, the neuromuscular junction (NMJ) of the Drosophila larva (c.f. Figure


The literature examining the relationship between cardiorespiratory fitness and the brain in older adults has increased rapidly, with 30 of 34 studies published since 2008. Here we review cross-sectional and exercise intervention studies in older adults examining the relationship between cardiorespiratory fitness and brain structure and function, typically assessed using Magnetic Resonance Imaging (MRI). Studies of patients with Alzheimer's disease are discussed when available. The structural MRI studies revealed a consistent positive relationship between cardiorespiratory fitness and brain volume in cortical regions including anterior cingulate, lateral prefrontal, and lateral parietal cortex. Support for a positive relationship between cardiorespiratory fitness and medial temporal lobe volume was less consistent, although evident when a region-of-interest approach was implemented. In fMRI studies, cardiorespiratory fitness in older adults was associated with activation in similar regions as those identified in the structural studies, including anterior cingulate, lateral prefrontal, and lateral parietal cortex, despite heterogeneity among the functional tasks implemented. This comprehensive review highlights the overlap in brain regions showing a positive relationship with cardiorespiratory fitness in both structural and functional imaging modalities. The findings suggest that aerobic exercise and cardiorespiratory fitness contribute to healthy brain aging, although additional studies in Alzheimer's disease are needed. Approximately 5.3 million Americans currently suffer from Alzheimer's disease  or as part of a composite measure of physical fitness , or an estimate of cardiorespiratory fitness, either derived from equations using age, gender, body mass index or inferred from self-report physical activity questionnaires . Reference sections of relevant articles were also examined to identify additional studies.Recent structural and functional Magnetic Resonance Imaging (fMRI) studies have provided support for a positive relationship between cardiorespiratory fitness and brain structure and function in humans. An examination of this nascent literature, which has seen a tripling in the number of peer-reviewed studies since 2008, may provide insight into brain regions most likely to be influenced by exercise in humans. Recent brief reviews on this topic have targeted children and older adults  brain structure and (2) brain function. Within each of these sections, we first review cross-sectional studies, followed by exercise intervention studies. Given that the medial temporal lobes (MTL), specifically the hippocampus, is one of the primary targets of physical activity effects in the rodent brain  consumption is measured throughout the test. Relevant measures include VO2 peak  and VO2 max . Cycle ergometer protocols are also used, although peak VO2 values tend to be 10–20% below those obtained using a treadmill protocol  in rodents with upregulation of neurotrophins , neurovascular plasticity (primarily via angiogenesis), and neurogenesis, as well as human studies linking aerobic training to enhanced cognition  have been used in a number of neuroimaging studies. Use of such questionnaires is based on the assumption that subjects who report greater amounts of physical activity are also likely to have higher physical fitness . The questionnaire approach is subject to reporting inaccuracies, omissions and bias, and misunderstanding questions  is assessed with methods other than the gold standard , the method of assessment is noted in the text. Finally, we note that there is a difference in the strength of the conclusions to be made for cross-sectional relative to intervention studies, with the primary caveat that cross-sectional relationships do not imply causation. That is, the cross-sectional studies indicate whether neural differences exist within subgroups of older adults (high vs. low cardiorespiratory fitness). Although observed brain differences are associated with cardiorespiratory fitness, it is possible that a number of unstudied factors may also influence the results, such as genetics, diet, blood pressure, etc. Indeed, results from cross-sectional studies should be interpreted with caution for this reason. Despite these potential issues, results from the cross-sectional studies were relatively consistent with findings from the intervention studies and therefore will be discussed in this review.Our review revealed a limited number of studies implementing the same fitness assessment techniques. A primary goal is to give a comprehensive review of neuroimaging studies examining cardiorespiratory fitness  in older adults. We considered studies using any of the fitness assessment techniques previously described and studies implementing aerobic exercise training aimed at enhancing cardiorespiratory fitness . We note the specific fitness assessment methods for each study in Tables To measure brain structure, voxel-based morphometry (VBM) is the most common analysis approach implemented in neuroimaging studies of fitness and brain structure (see Table 2 from Rockport one-mile protocol) was associated with attenuated age-related decline in tissue density in fronto-parietal white and gray matter regions including prefrontal cortex, superior parietal cortex, and temporal cortex in healthy older adults  in whole-brain VBM studies of older adults has been inconsistent, with only Gordon et al.  and Erics Figure . In anots Figure . This ef2 peak was positively associated with fractional anisotropy in the middle and posterior segments of the cingulum bundle  correlated with fractional anisotropy and radial diffusivity measures in the body and genu of the corpus callosum , a tracer known to accumulate in regions encumbered with amyloid deposits, researchers have demonstrated that in cognitively normal older adults lower levels of physical activity (assessed using a self-report questionnaire) are associated with increased amyloid burden in cortical regions  relative to a non-aerobic stretching control group . For example, increased volume of the anterior cingulate cortex, supplementary motor cortex, right inferior frontal gyrus, left superior temporal gyrus and anterior corpus callosum was reported in an aerobic training group . The results are nonetheless noteworthy because the data suggest that increases in physical activity, even at low intensity, may positively impact brain structure and memory performance. However, the lack of training-related change in the measure of cardiorespiratory fitness suggests the results should be interpreted with caution.Another study similarly found that increases in physical activity (assessed with a questionnaire) resulting from exercise training over a 6-month period were associated with gray matter volume increases in the cingulate gyrus (including both anterior and posterior cingulate cortex), left superior frontal gyrus, left medial parietal cortex, and regions of occipital cortex  relative to the stretching control group (1.1%). Collapsing across all subjects, change in cardiorespiratory fitness (VO2 max) was positively associated with hippocampal volume. Furthermore, aerobically trained older adults demonstrated an approximately 2% increase in hippocampal volume (left and right), whereas a decrease of roughly 1.4% was observed in the stretching control group  by 14.6%, whereas stretching, toning, and balance exercises increased cardiorespiratory fitness by 6.7%. There were no differences in white matter integrity as a function of training condition, although a trend for greater fractional anisotropy in a prefrontal ROI was observed for aerobically trained older adults relative to the non-aerobic group. Furthermore, there was a positive relationship between magnitude of change in cardiorespiratory fitness and fractional anisotropy values in prefrontal, parietal, and temporal ROIs in aerobically trained older adults. These effects were not observed in the non-aerobic training condition.Only one exercise intervention study has examined white matter structure using diffusion tensor imaging  and fMRI activity using a modified version of the Ericksen flanker task  was associated with greater activation in bilateral middle and inferior frontal gyrus and left superior parietal cortex  was related to brain activation while subjects imagined walking forward or backward. During imagined backward walking, high-fit older adults relative to low-fit older adults showed increased activation in supplementary motor area and ventral premotor cortex and reduced activation in several regions including right dorsolateral prefrontal cortex and left middle temporal gyrus. This pattern of activity was thought to reflect increased cognitive processing load in low-fit older adults, who may require more cognitive resources to activate internal motor representations than the high-fit older adults. In another study  during flanker task performance in a group of aerobically trained older adults relative to a stretching control group , a semantic memory retrieval task , and functional connectivity during passive viewing tasks. Importantly, these fronto-parietal regions appear to be the same regions showing structural associations with cardiorespiratory fitness. The majority of cardiorespiratory fitness-related patterns were increases in neural activity, with the exception of anterior cingulate cortex, which was associated with decreased activity in multiple studies. The decreased activity in this region was attributed to a reduction in neural resources necessary to resolve response conflict. The relationship between cardiorespiratory fitness and MTL function was less reliable for the fMRI studies, although this may be attributable to the lack of tasks implemented during fMRI that would be expected to elicit activation in MTL regions. There was also evidence to suggest a positive association of cardiorespiratory fitness with brain function in individuals with genetic risk for AD and those with mild cognitive impairment, but further evidence is needed as these studies did not directly measure cardiorespiratory fitness, but rather inferred fitness from self-reported measures of physical activity. We did not identify any fMRI studies examining the relationship between cardiorespiratory fitness and brain function in AD patients. This may in part be due to the challenges of conducting task-based fMRI in individuals who may not be able to learn and remember task instructions and may become confused during the course of the study. Given the cognitive impairment associated with AD and the cognitive demands for task performance during fMRI, one would likely need to test patients in the early stages of the disease, using simple cognitive tasks, or relying exclusively on resting-state fMRI (which does not require task performance).The extant data from both structural and functional neuroimaging studies support the notion that cardiorespiratory fitness links to neural integrity in older adults. Despite the differences in imaging modality and cardiorespiratory fitness assessment methods, there is consistency in the brain regions showing a relationship with cardiorespiratory fitness, as both cross-sectional and aerobic exercise training studies using functional and structural imaging have demonstrated a relationship with cardiorespiratory fitness in regions such as anterior cingulate cortex, medial and lateral prefrontal cortex, and lateral parietal regions. The relationship between cardiorespiratory fitness and structural integrity of the MTL is inconsistent in whole-brain VBM studies, although several ROI studies support the tenant that cardiorespiratory fitness is correlated with the structural integrity of the MTL. It is possible that the inconsistent MTIL results are attributable to the differences in statistical thresholding procedures implemented  for whole-brain relative to ROI studies. Cardiorespiratory fitness-MTL effects have not consistently been found in fMRI studies, likely due to the lack of studies using tasks that reliably elicit MTL activation.A remaining question is whether the consistent association of cardiorespiratory fitness with fronto-parietal regions observed across various tasks is attributable to shared cognitive component processes across these tasks. For instance, executive control processes may be an important component driving performance in both the flanker task and tasks of semantic memory retrieval. Alternatively, is there something about the neurobiological organization of frontal and parietal cortex (or its tendency to decline with aging) that makes these regions more sensitive to changes in cardiorespiratory fitness? Disentangling this issue will require the use of tasks tapping different cognitive functions during fMRI in the same group of participants. For instance, implementing a flanker task (executive control), face-name memory task (episodic memory), and face/scene viewing task  could potentially identify brain regions that are sensitive to cardiorespiratory fitness across tasks and regions that may show domain-specific relationships with cardiorespiratory fitness. We are not aware of any fitness studies that have implemented such an approach. Unfortunately, a quantitative meta-analytic approach to identify the exact neural coordinates of cardiorespiratory fitness was not possible in the present review, as the majority of studies did not present a table of significant cardiorespiratory fitness-brain region relationships in standard neuroanatomical space, as is required for such analysis  as the region most susceptible to effects of physical activity related to cardiorespiratory fitness, whereas in humans, the most consistent findings appear to localize to fronto-parietal regions. These neural findings mirror the cognitive findings, in which the impact of physical activity (wheel running) on behavior in rodents is most commonly associated with animal analogues of episodic memory tasks—that is, hippocampally-mediated tasks such as the Morris water maze or radial arm maze . Additional intervention studies are needed to examine dose effects that yield the strongest impact on cognition and the brain, including comparisons of frequency, intensity, and duration of exercise training. Although we have focused exclusively on cardiorespiratory fitness, two recent reports have examined the impact of resistance training on cognition on the brain, and suggest that resistance training may positively impact cognitive performance and brain function  have yet to be completed and intervention efficacy may be complicated by the presence of cardiovascular risk factors , albeit smaller than that typically seen for aerobically trained older adults  or subjective self-report measures of physical activity (questionnaires), which as noted previously, rely on the inference that higher levels of activity are associated with higher levels of fitness. We note that cardiorespiratory fitness and physical activity may not have an exact one-to-one relationship, as cardiorespiratory fitness is likely impacted by multiple factors , and therefore one could have high cardiorespiratory fitness but also be sedentary . However, data reveal a correlation between these distinct constructs across individuals (Bowles et al., The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Abnormal eye contact is a core symptom of autism spectrum disorders (ASD), though little is understood of the neural bases of gaze processing in ASD. Competing hypotheses suggest that individuals with ASD avoid eye contact due to the anxiety-provoking nature of direct eye gaze or that eye-gaze cues hold less interest or significance to children with ASD. The current study examined the effects of gaze direction on neural processing of emotional faces in typically developing (TD) children and those with ASD. While undergoing functional magnetic resonance imaging (fMRI), 16 high-functioning children and adolescents with ASD and 16 TD controls viewed a series of faces depicting emotional expressions with either direct or averted gaze. Children in both groups showed significant activity in visual-processing regions for both direct and averted gaze trials. However, there was a significant group by gaze interaction such that only TD children showed reliably greater activity in ventrolateral prefrontal cortex for direct versus averted gaze. The ASD group showed no difference between direct and averted gaze in response to faces conveying negative emotions. These results highlight the key role of eye gaze in signaling communicative intent and suggest altered processing of the emotional significance of direct gaze in children with ASD. Processing and interpreting eye gaze cues is crucial for social development. Neonates orient preferentially to eyes, young infants find direct eye contact physiologically soothing, and by 5 months of age, infants shift their own visual attention reflexively based on others’ eye gaze direction alone . Such eaThe brain appears to be especially sensitive to gaze direction in processing features of the face . BehavioGiven that gaze cues impart critical information regarding others’ feelings and intentions, it is not surprising that abnormalities in gaze processing are prevalent among individuals with autism, who display severe impairments in social functioning and understanding. Reduced attention to faces, and specifically the eyes, in the first year of life is associated with the development of autism . ToddlerWhy eye cues appear not to be as salient for individuals with autism, and how this relates to the abnormal development of other neural systems in childhood, is largely unknown. Neuroimaging studies have recently begun to address this issue showing, for example, that brain regions critical to processing shifts in gaze are insensitive to violations of contextual cues in adult individuals with autism spectrum disorders ASD;  as well Alternatively, children with ASD may engage in reduced mutual eye contact or gaze monitoring because it may be intrinsically less interesting to them, and/or may not carry the same informational value as for TD children. This alternative model proposes reduced social motivation and cue salience, and suggests that this reduced salience, in turn, may negatively affect the development of expertise with social and emotional cues in children with ASD . NeuroimThese two hypotheses make different predictions about brain activity during gaze and emotion processing. The former suggests that direct gaze, particularly in faces displaying strong affect, should produce hyperactivity in emotionally responsive brain regions, such as the amygdala and ventrolateral prefrontal cortex (VLPFC), areas known to be involved in emotion signaling, integration, and regulation . The latSixteen TD children  between the ages of 8–17 years (mean age 12.30) were gender-, age-, and IQ-matched to our sample of 16 children with ASD. For each child in the ASD group, a prior clinical diagnosis was confirmed in an initial lab visit using the Autism Diagnostic Interview, Revised  and AutiAll children underwent an event-related fMRI session during which they viewed photographs of emotionally expressive faces  through Presentation of the stimuli comprised 20 trials for each of the eight conditions  interspersed with null events. In the present study, we evaluated only the negative-valenced stimuli . Stimulus faces were presented in pseudo-random sequence for 2 sec each, yielding a run of 9 min in total. As children with ASD often have atypical gaze patterns, which may affect fMRI activation patterns , we presOne possible confound in neuroimaging studies of face and gaze processing tasks in autism is the possibility that children with ASD may not actually look at the eyes (or look less at the eyes than TD controls). Our paradigm was designed to address this concern as fixation crosses were presented on the screen for 1 sec precisely in the region where the eyes of the next stimulus would appear. Although we were unable to track subjects’ eye movements during scanning, eye fixation in response to the identical paradigm was assessed in 21 of the original 32 children who participated in the study (10 TD and 11 ASD) during a separate eye tracking session conducted to test whether this manipulation was effective in driving attention to the eye region.t = 0.63, P>0.50) or indirect  gaze, nor in the amount of overall looking time at the faces overall .During this second visit, we tracked eye movements while each child sat 50 cm in front of a monitor, observing the identical sequence of faces as they saw previously in the scanner. Eye movements were calibrated for each subject and confirmed before and after the gaze data. Using an infrared Tobii 1750 eye tracking system (Tobii Technology), which calculates visual fixation within 1 cm of accuracy, we compared the amount of time subjects spent looking at the face and at the eyes, both in raw numbers and in percentage of total trial time spent fixating in the eye region. The results of these analyses indicate that the use of fixation crosses at the eye level was successful in drawing attention to the eye region during stimulus presentation as no significant differences were found between the groups in the amount of time spent looking at the eyes either during direct  . Two additional volumes were discarded at the beginning of each run to allow for T1 equilibrium effects. In addition, a T2-weighted matched-bandwidth high-resolution anatomical scan (same slice prescription as EPI) was acquired for each subject  for registration purposes into a Talairach-compatible MR atlas .All functional images were registered using Automated Image Registration AIR; , wherebyhttp://www.fil.ion.ucl.ac.uk/spm). For each comparison of interest, we conducted within- and between-group random effects analyses using one- and two-sample t-tests, respectively, and defined statistical significance at a signal intensity magnitude of P < 0.01, and a corrected cluster size threshold corresponding to P < 0.05. All analyses reported were statistically corrected for multiple comparisons across the whole brain at the cluster level, unless otherwise noted.Statistical analyses were performed using SPM99 , medial temporal gyrus , and fusiform gyrus  to be reliably more responsive to viewing direct as opposed to averted gaze .In contrast, when TD children viewed these identical expressions in faces with averted gaze, we observed a striking difference in regional activation. While visual regions and fusiform gyri were almost identically activated, none of the areas active in gaze-direct conditions in frontal and prefrontal cortices, or in subcortical areas such as the amygdalae and caudate showed a statistically significant response relative to null events. A direct comparison of brain activity in response to gaze-direct versus gaze-averted negative emotion faces in the TD group  revealedP < 0.05, corrected for multiple comparisons at the cluster level). An exploratory threshold , revealed responses to negative-valence, direct gaze in left hippocampus, superior frontal gyrus, and medial parietal cortex, but we found no activity in VLPFC as had been observed in the TD group.When children with ASD viewed negative expressions with direct gazes , as withAlso unlike the TD group, while viewing these same expressions with averted gaze, the ASD group showed a nearly identical pattern of activity as that in response to viewing gaze-direct conditions. A direct statistical comparison of brain responses of the ASD group to gaze-direct versus gaze-averted conditions showed no significant differences in activation .P < 0.05, corrected for small volume at the cluster level), confirming greater activity in this region in the TD versus the ASD group for direct versus averted eye gaze.To directly test the hypothesis that TD children showed selectively greater activation during direct-gaze processing of negative emotional faces compared to the ASD children, we contrasted brain responses to negative emotions versus null events between the groups, using both within-group results as a combined mask to restrict our search only within those regions that showed significant activity in either group. Viewing negatively valenced, gaze-direct faces elicited greater activation in the TD group in one region only: bilateral VLPFC . In contIn the present study we found that TD children show marked regional increases in brain activity in response to negative emotional expressions conveying direct as opposed to averted gazes, where the facial expressions were otherwise identical. Sensitivity to this subtle stimulus alteration suggests that the significance of direct eye gaze in emotionally expressive faces is powerfully registered in the young brain during face processing. Interpreting and responding accordingly to whether or not cues conveyed about others’ mental or emotional states relate immediately to you or your actions is essential for successfully navigating a dynamic and complex social world. Processing direct gaze in faces displaying negative emotions generates a strong neural signature in the TD brain, marked by activity in a network of emotion-processing regions. The dynamic gaze-related component of face processing has been elegantly described and replicated in studies using moving eye stimuli, highlighting the importance of social context on neural response in both the adult and TD brain .Interestingly, brain activity in VLPFC in TD children was solely dependent on eye gaze direction in angry or fearful faces. VLPFC has been observed to respond during the labeling of negative emotions , as welldirectly relevant to the individual. In autism, it appears that processing this information in others’ faces, likely relying in part on regions sensitive to gaze direction, is abnormal or absent, even when visual perception is clearly intact.The region in VLPFC differentiating direct and averted gaze in TD children also differentiated the TD from ASD group activation during direct gaze. Although children with ASD attended to the same visual information and fixated equally on the features of the face as did TD children (as confirmed in a separate eye tracking session), our data suggest that the particular significance of the emotional information conveyed by the faces with direct gaze may have been processed differently by TD children. A direct gaze conveying a strong, negative emotion has immediate significance for the individual, signaling potential threat and critical social information . The same facial expression conveyed with an averted gaze changes the significance of that information, tagging it as less immediately relevant to the receiver. In our sample of TD children, VLPFC activation appears to occur not merely as a result of exposure to negative affect, but rather to negative affect that is perceived to be both VLPFC and the amygdala to be significantly reduced, however, while children with autism process fearful or angry faces, relative to typical levels, and that this difference is most pronounced in the processing of faces with direct gaze. Studies have reported heightened sensitivity to direct gaze in regions such as the amygdala and striatum in autism, supporting a gaze aversion hypothesis whereby individuals with autism avoid mutual gaze with others due to the overly arousing or aversive nature of such eye contact . As our paradigm encouraged each group to fixate on the eyes, these fMRI findings of somatosensory cortical activation in the ASD group are consistent with data from previous fMRI and eye tracking studies suggesting that children with ASD, unless otherwise instructed, may spontaneously use alternative strategies to process or interpret information in faces e.g., . FurtherThe findings of our study are also in line with other data reporting decreased frontal brain activity in children with autism to emotional and social cues, suggesting that children who develop autism may have reduced integrity of frontal-posterior brain connections , 2007. SOur experimental set-up with cross-hair fixation points preceding eye stimuli was designed to prevent gaze aversion or reduced fixation on the eyes in the ASD group, and our eye tracking data showed no group differences in gaze behavior in either gaze direction condition, making it unlikely that gaze aversion could have explained our results. Equivalent activation among ASD and TD children in visual-processing regions including the fusiform gyrus, which is critical for processing faces, further suggests that ASD and TD children spent equal time looking at the faces. Our inability to track eye fixation in the scanner during the fMRI sessions, however, represents a weakness of this study, which our separate eye tracking data can only indirectly address. Based on the eye-tracking findings, the fixation cross manipulation in our design may have helped equate fixation behavior between groups, as might have the fact that the ASD group represented a relatively high-functioning sample of children who, even without the fixation crosses, may not have demonstrated as dramatic fixation deviations as has been found in lower-functioning samples .proportion of time spent looking at other regions such as the nose or forehead, however, did show significantly increased activation in right VLPFC during the presentation of negative, direct-gaze expressions. The presence of this relationship when eye gaze is quantified as a fixation preference, but not when it is quantified in terms of raw time, points to the possibility that children with a more normative bias to attend to eyes also show more normative brain activity. Children who overall attended to the faces less, but gazed more exclusively at the eyes when doing so, or children who attended well to the faces but showed a more distributed pattern of fixation did not show this associated increase in activation in VLPFC.We found that the amount of time that children tended to fixate on the face or particular regions of the face (as measured in the separate eye tracking session) did not relate in either group to brain activity in the amygdala, right VLPFC, or left VLPFC. Children with ASD who tended to look more at the eyes during direct gaze faces as a As the first study to directly address how gaze may be processed along with emotional content in TD children and children with autism, our results suggest that high-functioning children with ASD may perceive the faces and gaze direction, but that this information may not be automatically translated into its communicative significance through the co-recruitment of prefrontal and limbic brain regions, as appears to occur in children without ASD. If this is the case, deficits in social comprehension and functioning may not result directly from avoiding the eyes, or having a physiological aversion to direct gaze, but rather because the significance of emotional expressions with direct gaze are not extracted from their corresponding facial cues. This would suggest that at least by later childhood, reduced mutual gaze might be due to the fact that observing direct gaze in another person is no more meaningful or rewarding than observing a gaze that is averted. The differences we report between neurotypical children and children with ASD who display marked social impairments highlight the importance of appropriate sensitivity to the eye gaze in navigating the social world and suggest that disordered development in ASD may directly result from failure to appropriately respond to these subtle social cues.


The global atmospheric circuit generates a permanent electric field between the Earth surface and outer atmosphere  detect electric fields around plants and learn to use them to decide whether or not to visit flowers. Using a Faraday pail to measure electric fields generated by bees and plants, the team described how a bee visit temporarily modifies the electric charge of (Petunia) flowers, suggesting that floral electric properties could be used by future visitors to assess the reward value without necessarily needing to probe the flower.Writing in e et al.  demonstrTo explore this possibility, the authors used differential conditioning in which bees were trained to associate an electrically charged feeder (30 V) with a sucrose reward (CS+) and an uncharged feeder with an aversive quinine solution (CS−). After extensive training , bees chose the rewarding feeder in around 80% of trials. Similar levels of performance were observed when bees were trained with two feeders carrying the same charge but different electric field patterns (homogeneous vs. bull's eye shape), indicating that these insects can learn both the magnitude and geometry of an electric field. Bees learned to perform even better in discrimination tasks if the two feeders differed both in color (shade of green) and their electric field pattern compared to if they differed only in color. Natural electric fields around flowers may therefore contribute to the multimodal sources of information that bees use to learn and memorize floral rewards, in conjunction with color, pattern, shape, texture, humidity, or warmth  in various contexts, including during the “waggle dance”: the figure-of-eight-shaped circuit performed by foragers upon their return to the nest to communicate the location of rewarding flowers to nestmates (Von Frisch, In another study published in the s et al.  went a sTo identify the sensory receptors involved in electroreception the authors used proboscis extension response conditioning, a classical paradigm to study olfactory learning and memory Tadeka, . HarnessThe observation that insects can sense electric fields is not new. Indeed, it has long been known that electric fields induce a range of behavioral responses in ants, cockroaches, mosquitoes, fruit flies, and bees [reviewed in Jackson et al. ]. Howeve


Patient choice has become an increasingly visible part of publicly funded health care systems. Since the 1990s, many individuals have gained the ability to select their insurer in social health insurance funded systems, while in tax-funded health systems many patients can now select their primary care and hospital providers. Second opinions about clinical procedures are part of this broad movement toward increased patient involvement in care-related decision-making. One interesting policy question will be whether the coming period of financial austerity will strengthen or weaken the role of choice as health systems seek to deal with the inevitable mismatch of demand for and supply of medical resources. Seeking a second opinion  is part This complex framework of patient choice has grown considerably over the past 25 years. A combination of better informed patients and, in some systems, substantial waiting lists have pushed policymakers to open up what previously had been an expert-determined planning process. Planners’ concerns that allowing choice would cost more (due to extra capacity) as well as reduce overall equity have largely been replaced by politicians’ concerns that they not be blamed by increasingly vocal patients for inadequately responsive provider institutions.This growth in patient choice also represents a desire of many patients to participate in their own medical decision-making . A wholeOne interesting issue is how well this entire apparatus of patient choice –potentially including second opinion– will sustain itself as health systems confront what is shaping up to be a new era of permanent austerity . While tPatients, conversely, may well push for increased choice options, especially if the austerity process results in making patients contribute more out-of-pocket to the overall cost of the procedures they receive. If they have to pay more, they may reason, they ought to have more of a say in deciding what should be done. This may especially apply to second opinions for expensive and invasive clinical procedures. Increased patient expectation of participation in medical decision-making may also develop if some tax-funded health systems, facing serious funding shortfalls, turn to private providers for particular procedures where private provision  may be cheaper.Dr. Saltman has no commercial conflicts of interest.Richard B. Saltman is Professor of Health Policy and Management at the Rollins School of Public Health at Emory University in Atlanta. He is also Associate Director of Research Policy at the European Observatory on Health Systems and Policies in Brussels.Commentary on the paper by Greenfield, Pliskin, Wientroub, Davidovitch: Orthopedic surgeons’ and neurologists’ attitudes towards second opinions in the Israeli healthcare system: a qualitative study.