The increasing ubiquity of haptic displays  necessitates a better understanding of the perceptual capabilities of the human haptic system. Haptic displays will soon be capable of locally deforming to create simple 3D shapes. This study investigated the sensitivity of our haptic system to a fundamental component of shapes: edges. A novel set of eight high quality shape stimuli with test edges that varied in sharpness were fabricated in a 3D printer. In a two alternative, forced choice task, blindfolded participants were presented with two of these shapes side by side  and after actively exploring the test edge of each shape with the tip of their index finger, reported which shape had the sharper edge. We used a model selection approach to fit optimal psychometric functions to performance data, and from these obtained just noticeable differences and Weber fractions. In Experiment 1, participants performed the task with four different references. With sharpness defined as the angle at which one surface meets the horizontal plane, the four JNDs closely followed Weber’s Law, giving a Weber fraction of 0.11. Comparisons to previously reported Weber fractions from other haptic manipulations (e.g. amplitude of vibration) suggests we are sufficiently sensitive to changes in edge sharpness for this to be of potential utility in the design of future haptic displays. In Experiment 2, two groups of participants performed the task with a single reference but different exploration strategies; one was limited to a single touch, the other unconstrained and free to explore as they wished. As predicted, the JND in the free exploration condition was lower than that in the single touch condition, indicating exploration strategy affects sensitivity to edge sharpness. While it has long been known that haptic feedback improves the usability of a haptic interface When we handle an object, many of its material properties provide enough information for it to be identified using haptic information alone; its volume, compliance, thermal characteristics, and surface texture all give clues to its identity After vision, the haptic modality is the only other sense through which to perceive directly shape information. Therefore, to benefit individuals with visual impairments, it is important to design haptic displays which can convey shape information effectively. One mechanism commonly employed to display shape information is a two-dimensional, raised-line drawing, in which an outline of an object or scene or perhaps a more abstract image is ‘drawn’ in edges raised above the background , all rely heavily on the ability to detect edges. What do we know of the characteristics of physical edges and the sensitivity of our haptic system to these characteristics? If we define an edge as being formed by the juncture of two surfaces, a fundamental property of an edge will be the angle at which these surfaces meet (the apex in two dimensions and the vertex in three dimensions); in a three dimensional shape that property of an edge also relates to the psychological dimension of Researchers have investigated our ability to discriminate the curvature of surfaces using stimuli that are both real Park and colleagues Before describing our study, it is worth briefly reviewing the work on 2D angle discrimination, because it is the 3D equivalent of the apex (the vertex) that determines the sharpness of an edge. However, there is a clear distinction here: we are interested in the sharpness of 3D shapes and the previous studies on apex discrimination have typically used chevron shapes on the horizontal plane  and have allowed participants to explore the arms of the chevron shape, whereas our study excludes face exploration  and focusses on edge exploration in the vertical plane. Using stimuli consisting of raised chevrons in the horizontal plane, Wijntjes and Kappers Voisin and colleagues In our study, we make use of state-of-the-art 3D printing technology to produce a set of three-dimensional shape stimuli with edges that vary in sharpness. We reasoned that, while at some scale all edges are rounded at their apex, at the scale of our everyday industrialised environment, objects can appear to have edges that have no perceivable apex curvature and are sharp to the touch. Our sensitivity to changes in sharpness may be qualitatively different to our sensitivity to changes in curvature. To test this, the edges of our stimuli were true, sharp edges with no perceivable apex curvature.As with many psychological phenomena, it is likely that our sensitivity to changes in edge sharpness will change over a range of sharpness. Indeed, an important characteristic of the perception of any class of stimuli is the way in which discrimination thresholds scale as the magnitude of stimulus scales, and classically, the extent to which this follows Weber’s Law. Our first experiment explored this, and measured the JND in edge sharpness using a number of reference edges . We examine how the Weber fractions scale across these different conditions, and how these relate to the Weber fractions reported in studies of 2D angle and curvature discrimination.Exploration strategy can have a significant impact on performance in haptic discrimination tasks Both Experiments were approved by the Faculty of Science Ethics Committee of the University of Bristol. All participants were volunteers who gave written informed consent.Experiment 1Fifteen participants  completed the task. For the 90° condition, only nine participants’ data was analysed. A visual inspection of the data after six participants indicated performance was far better than expected, meaning we may not have had sufficient data points around the JND to estimate it adequately. To address this, we changed the comparison stimuli in the 90° condition from participant seven to increase task difficulty. All participants were undergraduate students from the University of Bristol who were paid £40.A novel set of 3D, triangular prism shapes, with test edges of varying sharpness, were produced using 3D printing technology. The test edge was the edge running along the upper apex of the triangular prism. All shapes shared the same base area of 36×60 mm and had the same height of 26 mm. The sharpness of the test edge was altered by varying the angle at which the two upper surfaces met to form the apex, and this angle, θ, was used as our measure of sharpness.The shapes were fabricated on an envisionTEC Perfactory 3 printer using RCP30 nano cured ceramic photo polymer. The Perfactory 3 has an XY resolution of 30 µm and a Z resolution of 15 µm. To minimise texture along the test edge, enabling participants to focus on judgements of sharpness alone, shapes were fabricated such that the 60 mm test edge was aligned with the higher resolution Z axis. In subjective handling, the test edges of all shapes were very smooth with no noticeable texture or imperfections.θ,Δ from 5° to 35° in 5° increments in each condition. Given the relatively limited range of sharpness available, and the lack of a prediction of the likely value of JND, we set the reference to one end of the range of test stimuli in each condition to maximise the chance we would capture the JND. In the θ = 40° and 50° conditions the comparison shapes were all greater in sharpness than the reference, and in the θ = 70° and 90° conditions, they were all less sharp.Eleven shapes were produced with edges that ranged in sharpness from θ = 40° to θ = 90° in 5° increments. We did not produce shapes with edges of sharpness greater than θ = 90°, because exploration of edges with such low sharpness may involve the larger scale sensing of the angle between two separate faces rather than the sharpness of the edge itself. At this time, fabrication is expensive and lengthy, and this further limited the number of shapes we could produce. We selected four shapes distributed approximately evenly across our range of shapes  and used these as references in Experiment 1. For each reference we used seven comparison shapes, giving a range of differences in sharpness, Participants were blindfolded to prevent perception of visual information from the stimuli, and to ensure non-informative vision had no effect on their haptic perception The method of constant stimuli was used to obtain a set of psychometric data from which the discrimination threshold could be determined. Participants were presented with the reference shape paired with each of the seven comparison shapes 40 times , making a total of 280 trials per session. The order of trial presentation was randomised across the session. Each session was divided into four blocks of 70 trials, each lasting approximately 15 minutes, with a rest period between each block. Participants completed the four different reference tasks (one per session) in an order determined by a partial Latin square to minimise order effects.Participants were instructed to explore the edges of the shapes with a single stationary touch of the fingertip of the index finger of their dominant hand. They were asked to aim their touch at the approximate mid-point of each edge, avoiding the corners of the edge, and to keep the touch static, without any movements that may result in contact with the surfaces of the shape. They were not permitted to return to either shape for a second touch.correctP) and sharpness difference (θΔ) asω is a lapserate parameter that we have included to represent the proportion of responses on which a participant guesses .To estimate the JNDs, we fit a series of psychometric functions to our data. Typically, within the field of haptic perception, the function used has been the logistic. Such a function can model the relationship between proportion correct (λ) whilst also being able to adjust the curve’s form using its shape parameter (k). This allows us to have a much finer control of the relationship between sharpness difference and proportion correct than that offered by the logistic described above. Therefore, for each participant, in addition to the logistic, we model their data using the following relationshipf is the cumulative Weibull distribution at sharpness difference θΔ.However, we deliberately sampled our psychometric functions at enough locations, and with enough precision, to build up a good idea of the shape of the relationship between sharpness difference and proportion correct. In addition to the logistic, we therefore used the cumulative Weibull distribution appropriately scaled between 0.5 (chance performance) and 1 (perfect performance) to model our data. Note that scaling the function between 0.5 and 1.0 allows us to shift the curve sideways using its location parameter  to select the model that optimally described our data . Models with lower AICs are preferred; the difference between AICs indicates the strength of that preference. We fit each model by maximising their likelihood given the data using Matlab’s Results for both the logistic and Weibull models are shown in θΔ. The model we therefore use to analyse the discrimination thresholds is a Weibull with no lapsrate, a shape parameter for each reference, and a separate location parameter for each participant. The best fitting model for each individual is shown in Next, we considered whether parameter values varied across reference set. In this case we have two variations of model, one where the shape parameter is the same across standards and one where it is free to differ across standards. The latter is strongly preferred with an AIC that is 20.9 less than that of the model with shape fixed across standards, suggesting that choice of standard affects the relationship between sensitivity and degree of difference, Fourteen participants  completed the task using the Single Touch strategy, and 15 different participants  completed the task using the Free Exploration strategy. All participants were undergraduate students from the University of Bristol who participated for course credit.The 70° reference set of stimuli from Experiment 1 were used (stimuli differed from 5° to 35° in steps down of 5° from the 70° referent).The design and procedure were identical to Experiment 1, except participants were only exposed to the 70° reference set and they either explored with a Single Touch strategy or a Free Exploration strategy. The single Touch strategy was identical to the procedure used to explore the edges in Experiment 1.The procedure for the Free Exploration strategy was identical to that used in the Single Touch strategy, with the only exception that participants were free to use a different strategy to explore the edges of the shapes. They were again instructed to explore the edges of the shapes with the fingertip of the index finger of their dominant hand, and to avoid touching the corners of the edge. But with the Free Exploration strategy they were not constrained in terms of the way they should touch the shapes, the number of touches they should use, or the order in which to explore the shapes. They were allowed to move their exploration between the two shapes at will, as long as they continued to avoid the corners of the edges, in particular those at the boundary of the two shapes.We completed an analysis similar to that of Experiment 1, fitting both the logistic and Weibull functions to the individual participants’ data. To simplify the search space, we first looked separately at models within the results for each exploration strategy. Results for both the logistic and Weibull models are shown in θΔ. We use this model to analyse the thresholds and the best fitting model for each individual participant is shown in The best fitting model was the same as Experiment 1: A Weibull with no lapsrate, a separate location parameter for each participant and a shape parameter shared across participants. This model fit six times as well as the next best fitting model (which included the lapserate). Whilst the latter is still a reasonable candidate, we note that the estimated lapserates are small (0.0012 for the Single Touch strategy and 0.0085 for the Free Exploration strategy) and make little difference to the other parameters. Next, we considered whether parameter values varied between exploration strategies. In this case we have two variations of the model, one where the shape parameter is the same across strategies and one where it is free to differ across strategies. The latter is strongly preferred with an AIC that is 18.2 less than that of the model with shape fixed across strategies, suggesting that exploration strategy affects the relationship between sensitivity and degree of difference, As a useful guide for future experiments using sharpness that need an estimate of a shape parameter , we fitted the Weibull across all our data sets from Experiment 1 and Experiment 2 with the shape parameter fixed to provide an estimate of the best-guess shape parameter to use. The resulting shape value was 1.07  is constant across different levels of reference. Following the approach of Park and colleagues An alternative to our original approach of measuring sharpness as the internal angle between the two sides of the edge is to redefine sharpness as the open angle formed between one surface and the horizontal plane, as shown in Park et al. θ.Δ The typical increase in accuracy with increased θΔ is evident. The data for individual participants are provided in file t(27) = 2.63, p = .014).The decreased threshold using the Free Exploration strategy is expected, because an unconstrained exploration provides many opportunities to gather more information than a single touch, enabling more accurate discrimination and a consequent lowering of discrimination threshold. A similar dependence of discrimination threshold on exploration strategy has been observed in many previous studies of haptic discrimination The first was simply to touch the edges more than once. A multiple touch advantage has been reported in many investigations of haptic performance, with, for example, a reduction in texture discrimination thresholds The second type of exploration was to move the glabrous skin of the fingertip in a slow, fore and aft movement over the edge. Interestingly, this is similar to the particular exploration procedure Lederman and Klatzky The third type of exploration strategy was to slide the glabrous skin of the fingertip along the edge of the shape in a lateral movement. This may produce a similar sensation as that from the fore-aft movement. We are conducting further investigations of these three possible exploration strategies to determine which of them (or which combination) leads to the improved discriminability.The current studies demonstrated that thresholds varied as a function of the reference, with lower thresholds for larger angles. Using a free exploration strategy as opposed to a ‘tactile glance’ significantly lowered the threshold. The Weber fraction for sharpness  was 0.11.Our data analysis clearly identified the Weibull as the most appropriate model to use. However, there is inconsistency in the haptic literature both about which model to use  and about which threshold to use . Thus, it is often difficult to compare results across studies. Compounding the problem is the fact that the Weber fraction  is dependent on the measure which is chosen to represent the magnitude of a stimulus. In our study, using the definition of sharpness as the internal angle formed by the junction of two faces results in a larger Weber fraction (suggesting relatively poor performance) than using our second measure of sharpness, the angle formed by one face and the horizontal plane. The latter preferred measure leads to an increase in sharpness with an increasing angle and produces a relatively constant Weber fraction over the range of thresholds. Using this measure essentially divides our thresholds in half, leading to ‘better’ performance. Both measures of sharpness are legitimate, but lead to different conclusions when considering the relative discriminability of sharpness compared with, for example, 2D angle as measured by Voisin and colleagues In the real-world, two surfaces will rarely meet to form a perfect, sharp edge, and the edge formed will be curved to some degree. This means the sharpness of real edges may best be considered as having two components, namely, the angle at which the surfaces meet and the curvature at the point the surfaces meet. Teasing apart these two components and investigating our sensitivity to these independently is likely to be a worthwhile endeavour for future investigations.Sharpness thresholds, like other tactile thresholds, will be affected, not only by the characteristics of the edges themselves, but also by the characteristics of the skin touching the edge. The distribution of mechanoreceptors in the skin covering different parts of the body varies considerably and these differences will result in different thresholds in haptic spatial discrimination In summary, many devices with haptic interfaces remain unused, often because they continue to be designed without knowledge of the limitations of our haptic system Figure S1Data from Experiment 1 using a 40 degree standard, showing proportion of correct responses as difference in sharpness between reference and test shape varies. Curve shown is best fitting cumulative Weibull function.(TIF)Click here for additional data file.Figure S2Data from Experiment 1 using a 50 degree standard, showing proportion of correct responses as difference in sharpness between reference and test shape varies. Curve shown is best fitting cumulative Weibull function.(TIF)Click here for additional data file.Figure S3Data from Experiment 1 using a 70 degree standard, showing proportion of correct responses as difference in sharpness between reference and test shape varies. Curve shown is best fitting cumulative Weibull function.(TIF)Click here for additional data file.Figure S4Data from Experiment 1 using a 90 degree standard, showing proportion of correct responses as difference in sharpness between reference and test shape varies. Curve shown is best fitting cumulative Weibull function.(TIF)Click here for additional data file.Figure S5Data from Experiment 2 using a 70 degree standard and single touch exploration strategy, showing proportion of correct responses as difference in sharpness between reference and test shape varies. Curve shown is best fitting cumulative Weibull function.(TIF)Click here for additional data file.Figure S6Data from Experiment 2 using a 70 degree standard and free exploration strategy, showing proportion of correct responses as difference in sharpness between reference and test shape varies. Curve shown is best fitting cumulative Weibull function.(TIF)Click here for additional data file.Table S1Model selection for Experiment 1 using AICs.(DOCX)Click here for additional data file.Table S2Model selection for Experiment 2 using AICs.(DOCX)Click here for additional data file.Dataset S1Tab-delimited text file, with column headings, containing the complete data from Experiment 1.(TXT)Click here for additional data file.Dataset S2Tab-delimited text file, with column headings, containing the complete data from Experiment 2.(TXT)Click here for additional data file.


N-glycosylated. This complex formation is catalyzed by the posttranslational protein processing system of the endoplasmic reticulum (ER). Others have reported that in plaque Aβ is present only as the naked peptide. Together these results suggest that both plaque and dementia are secondary to an age related decline in the capacity of the ER to catalyze protein, posttranslational processing. Since the synaptic membrane proteins necessary for a functioning memory are also processed in the ER, these findings would suggest that the loss of cognition is due to a decline in the capacity of the neuron to produce and maintain functioning synapses. Work from my laboratory and from others further indicate that the components of the ER, posttranslational, protein processing pathway do dramatically decline with age. These data suggest that this decline may be found in all cells and could account not only for the dementia of Alzheimer’s disease, but also for many of the other manifestations of the aging process. These observations also suggest that declining ER function has a role in two well-recognized phenomena associated with aging: a loss of mitochondrial function and a decrease in myelin. Finally, based on this paradigm I propose new cellular and animals models for high-throughput screening for drug discovery.It is currently thought that the dementia of Alzheimer’s disease is due to the neurotoxicity of the deposits or aggregates of amyloid-β (Aβ) in the extracellular space of the cerebral cortex. This model has been widely criticized because there is a poor correlation between deposits and dementia. Others have questioned whether Aβ is truly neurotoxic. Yet, in spite of these concerns, the search for therapeutic agents has been based on the development of mouse models transfected with mutant genes associated in humans with early onset Alzheimer’s disease. A major limitation of these models is that although they exhibit many of the pathological and clinical manifestation of the human disease, the bulk of individuals who develop the dementia of Alzheimer’s disease have none of these mutant genes. Furthermore, nine clinical trials of drugs that were effective in transgenic mice failed to show any benefit in patients. Finally, a major unresolved issue with the Aβ model is that since Aβ is produced in everyone, why are deposits only seen in the elderly? This issue must be resolved if we are to understand the etiology of the disease and develop test systems for both diagnosis and drug discovery. Published studies from my laboratory demonstrate that in human cerebrospinal fluid immunoreactive Aβ is only present as a complex with two chaperones, ERp57 and calreticulin and is  It is currently thought that the dementia of Alzheimer’s disease is due to the neurotoxicity of the deposits or aggregates of amyloid-β (Aβ) in the extracellular space of the cerebral cortex. In support of this model various familial forms of the disease are characterized by the early deposition of plaque and the development of dementia. In light of the similar pathology observed between the familial forms and the sporadic disease, many workers have developed transgenic mouse models in which the animals were transfected with mutant forms of the amyloid precursor protein (APP) and/or presenilins 1 and 2. The APP normally is cleaved to form two growth factors, αsAPP and βsAPP while the presenilins are components of the γ secretase which clips the Aβ from the membrane. The αsAPP is fifty times more active than βsAPP’s , but theYet, a major philosophical problem with this approach is that the vast majority of the elderly with late onset disease do not have these mutations. In fact in genome wide association studies the most consistently observed genetic variants associated with the late onset disease are found in the apoE and clusterin genes. Furthermore, another difference between the late onset and familial forms is that in human studies Knockout studies of APP have reported that this growth factor is necessary for normal neuronal development . FurtherTable 1).Of greater concern there have been nine phase III clinical trials of agents that were effective in transgenic mice but failed to show any efficacy in patients with late onset disease  trial of o biloba  and the o biloba .G. biloba the subjects were followed for 7 years . This would seem to be a somewhat hazardous approach for the long term treatment of patients with cognitive impairment, since knocking out BACE1 has been shown to lead to significant deficits in brain function . This enzyme cleaves APP at the site which yields the Aβ peptide and the βsAPP (function . The mosn slices . In a shtau (P-tau). The P-tau then aggregates to form tangles. In a small phase II trial patients receiving 138 mg per day of the drug showed a markedly reduced cognitive decline during a 1 year study period. Yet, those receiving twice the dose showed a parallel decline to the placebo. A chemical modification of this agent is currently going into a phase III clinical trial. It will be interesting to see whether they can replicate their initial findings.The only agent which has actually shown any promise of a viable treatment for Alzheimer’s disease is methylene blue . This drIn light of these failures it would seem reasonable to examine new paradigms for the etiology of this dreaded condition. A number of years ago we asked the question:Since Aβ is produced in everyone why is plaque only seen in the brains of the elderly?Figure 4; We postulated that normally Aβ is bound to proteins which keep it in solution and thereby prevent plaque formation. And indeed this turned out to be the case! When we ran western blots of fresh or fresh frozen cerebrospinal fluid (CSF) on denaturing gels, we observed that there was only a single Aβ-immunoreactive band which was consistently found at around 62 kDa .Furthermore, on immunopurification we were able to isolate the complex with antibodies to either Aβ or ERp57 .A large number of studies on the biochemistry of the ER, posttranslational, protein processing pathway have reported that ERp57 binds to nascent proteins at The fact that the Aβ and the two chaperones all shifted to this higher molecular weight along with the immunopurification data strongly supports our claim that the Aβ band is not either of the two sAPP’s which have similar molecular weights.Figure 7).Finally, since the Aβ found in plaque is only present as the naked peptide, one possibility is that the complex was originally in the plaque but broke down when it was solubilized by the usual treatment with either concentrated formic or trifluoroacetic acid. This is not likely to be the case since treatment of CSF under these same conditions had no effect on the complex (channels 3 and 4) . In fact the only procedure which did affect the complex was storage overnight at 4°C in a pH 9.0 buffer (channel 9). The other interesting aspect of this study was that the complex bound to a bonate column, a synthetic lectin, suggesting that the Aβ is glycosylated (channel 8).++ uptake from the intestines. The ERp57 would appear to have a role in signal transduction since knocking it down or inhibiting it with antibody to its terminal carboxy end inhibited 1,25 dihydroxy vitamin D stimulated Ca++ uptake .Several other ER chaperones showed similar declines . Dolichol is a high molecular weight terpine which serves as a cofactor for the cytosolic synthesis of the oligosaccharide. Once the complex is fully synthesized, it is transferred to the lumen of the ER and attached to an ξ-amino group of an asparagine by an oligosaccharide transferase . These transmembrane proteins are located in both the ER membrane and the outer membrane of the mitochondria. Both mfn1 and 2 undergo posttranslational processing in the ER. Hence, a decline in the capacity of the ER to catalyze their posttranslational processing would be expected to have a profound effect on mitochondrial structure and function. Such declines in ER function could compromise the ability of the cell to maintain metabolically active mitochondria.A final role for the ER in maintaining mitochondrial structure and function is the control of mitochondrial fission and fusion. As defective mitochondria are cleared by autophagy, they are replaced through a process involving both mitochondrial fission and fusion. Recent studies have indicated that several proteins in the MAM play major roles in both of these processes . In partFigure 11). This structure is also processed in the ER. The observed decline seen with age in the capacity of the ER to catalyze this processing could explain the loss of white matter consistently seen in the elderly and the slowing of thought processes as we age.Finally, the myelin sheaths are the plasma membranes of oligodendrocytes and Schwann cells , are embedded in an exon of the otherwise intact target gene. This should maximize the number of potential target sites for small molecule, drug discovery.Such transgenic models are created in embryonic or induced pluripotent stem cells by homologous recombination using a variety of site specific endonuclease systems. These models are usually created with either mouse or human embryonic or induced pluripotent stem cells. In the case of the mouse lines it would also be possible to clone the cells and create transgenic, adult animals. This is an important step since it is necessary to demonstrate that the insertion of the fluorescent protein does not lead to an animal with compromised metabolism. Usually the indicator system is inserted in either the first or last exon of the native protein. If these turn out to produce metabolically compromised cells, then it would be necessary to insert the indicator in an exon that does not compromise metabolic function. The stem cells can then be transformed into a variety of tissue types by incubating with the appropriate growth factors. With the construction of the labeled cell lines, they can be used to automatically screen large libraries of compounds in microtiter plate readers.N-glycosylation pathway are lethal mutants. The possible approaches could include a lox-cre system in which the specific tissue cell type, such as neuronal cells have a haploid knock out of the critical gene. Alternatively, it is possible to develop models with a global knock down of the target gene(s) with synthetic, antisense oligonucleotides.Similarly intact animals models could be developed in which the relevant proteins have been knocked down. It is necessary to only knock them down because knockouts of the chaperones and components of the Figure 12).In an unrelated study of the toxicity of methoxychlor, we observed that feeding this insecticide to rats for 3 weeks specifically increased the levels of ERp57 in hepatic microsomes (ER) (1. Nine phase III clinical trials of agents that were effective in transgenic mice were not effective in patients with late onset dementia.2.N-glycosylated and bound to two ER chaperones, ERp57 and calreticulin, which keep it in solution. The reason that plaque does not form in the young is because Aβ is normally 3. These components decline with age.4. These findings suggest that the dementia seen in late onset Alzheimer’s disease is due to a decline in the ER, posttranslational processing of the synaptic, membrane proteins that are necessary for a functioning memory.5. It also suggests that the loss of mitochondrial function and white matter in the elderly is due to this decline in ER function.6. This paradigm suggests new cellular models for drug discovery in which fluorescent proteins are inserted into an exon of the various components of the ER, posttranslational, protein processing pathway.7. Animal models could be constructed in which the critical proteins are knocked down by standard procedures and then candidate drugs are administered to test whether they improve cognition.Finally, over the past two decades the pharmaceutical industry and funding agencies and foundations have made and are continuing to make massive investments in the search for disease modifying treatments for Alzheimer’s disease and other diseases of the elderly. Although these efforts have taken a variety of approaches, the bulk have sought treatments based on the Aβ hypothesis that seek to improve cognitive function by decreasing the brain content of Aβ. Considering the number of these agents currently in the pipeline, it is clear that this approach will continue to dominate drug development for the foreseeable future. Yet, since many of these new agents are merely variations on earlier failed investigational drugs, there is a significant probability that they too will not prove to be efficacious in phase III clinical trials.tau. Yet in the recent failed bapineuzumab trial, P-tau levels did decline, but the patients still showed no clinical benefit (In view of the long, lag period between the initial identification of new targets and the final regulatory approval of agents developed on the basis of new paradigms, it would seem prudent at this point to consider other models for drug discovery in case the current batch of investigational drugs fail to fulfill their early promise. At the present time there is little chance that this lag period can be foreshortened by evaluating therapeutic efficacy based on surrogate measures, because changes in the levels of such measures have not been demonstrated to correlate with clinical efficacy. For example, the two most widely accepted biomarkers in the CSF of disease status are low levels of Aβ and high levels of P- benefit .Many have cited the experience in the treatment of hypertension in which demonstrating that decreasing blood pressure was sufficient grounds for drug approval. But this surrogate measure was based on clinical trial data that had shown that a decrease in blood pressure led to a pronounced decrease in morbid events ,1970. InThe author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Retinal implants have been developed to treat blindness causing retinal degenerations such as Retinitis pigmentosa (RP). The retinal stimulators are covering only a small portion of the retina usually in its center. To restore not only central vision but also a useful visual field retinal stimulators need to cover a larger area of the retina. However, large area retinal stimulators are much more difficult to implant into an eye. Some basic questions concerning this challenge should be answered in a series of experiments.Large area retinal stimulators were fabricated as flexible multielectrode arrays (MEAs) using silicon technology with polyimide as the basic material for the substrate. Electrodes were made of gold covered with reactively sputtered iridium oxide. Several prototype designs were considered and implanted into enucleated porcine eyes. The prototype MEAs were also used as recording devices.Large area retinal stimulator MEAs were fabricated with a diameter of 12 mm covering a visual angle of 37.6° in a normal sighted human eye. The structures were flexible enough to be implanted in a folded state through an insertion nozzle. The implants could be positioned onto the retinal surface and fixated here using a retinal tack. Recording of spontaneous activity of retinal neurons was possible in vitro using these devices.Large flexible MEAs covering a wider area of the retina as current devices could be fabricated using silicon technology with polyimide as a base material. Principal surgical techniques were established to insert such large devices into an eye and the devices could also be used for recording of retinal neural activity. Retinal degenerations such as Retinitis pigmentosa (RP) may cause bilateral blindness. It is estimated that in Germany about 15,000 subjects are legally blind due to this disease. Although it is known that the disease is caused by a variety of mutations in several genes coding for key enzymes involved in retinal metabolism and light processing  no treatTo get an idea of the behavior of a polyimide foil within an eye, we created a very simple model for Comsol, a common finite element simulation software. The model consists of an incompressible spherical shell made of steel with an inner diameter of 22 mm and a polyimide foil with a thickness of 100 μm, a disc shape and a circular hole in the center of the structure. Then the foil was vertically moved into the shell until both parts came into contact. The Young’s modulus of the polyimide PI2611 we used in this simulation was 8.5 GPa and was taken from the material data sheet, the poisson ratio of 0.23 was taken from Patel et al. . The friFabrication of the stimulator prototypes takes place on silicon wafers as described in detail in Figure The surgical approach was simulated by performing the procedure in enucleated porcine eyes. The setting was the same as in real surgery. Operations were performed by experienced retinal surgeons using a surgical microscope. Removal of the lens was done by phacoemulsification and removal of the vitreous by vitrectomy using a 20 gauge 3 port approach. Visualization was achieved with endoillumination and a 130° contact lens placed on the corneal surface. Insertion of the device was done either by a scleral incision or by corneal incisions of 6 mm. Insertion of the device was facilitated by using a plastic nozzle.Healthy Wistar rats were dark adapted for one hour and decapitated in deep anaesthesia. Retinas were taken from the eye under dim red light. The electrodes of the VLARS MEA were connected to a multichannel recording and stimulating device . The isolated retina was placed onto the VLARS MEA with the ganglion cell side adjacent to the electrodes. The retina was permanently superfused for at least 45 minutes with Carbogene  saturated Ames Medium . For electrical stimulation a biphasic 40 μA current pulse with a cathodal and anodal phase duration of 500 μs was chosen. Light stimulation was done using a 1 second white light flash. The stimulation and recording was done with the MEA-Software MC_Rack . For spike detection raw data sets of 3-5 minutes continuous recording were analyzed with a 300 Hz high-pass filter and a 3000 Hz low-pass filter and an amplification gain factor of two. The data sampling rate was 25 kHz/channel. To distinguish spike waveforms on one electrode spikes were sorted computer based and manually with spike sorting software Offline SorterTM  before response analysis was done .http://www.arvo.org/About_ARVO/Policies/Statement_for_the_Use_of_Animals_in_Ophthalmic_and_Visual_Research/] and in accordance to the German Law for Animal Protection after approval obtained from the local government.All animal experiments were done in accordance with the ARVO statement for the use of animals in ophthalmic and visual research . Bo. Bo10]. 2. A retinal stimulator of that size could restore a visual field of about 18.8° covering a corresponding visual angle of 37.6° when implanted in a human eye of normal size. Additionally, more than 250 electrodes can be placed on such a device with current available technology.The VLARS project was started to develop a stimulator MEA covering a larger visual field. We built a device with a diameter of 12 millimeters covering a retinal area of about 110 mmLarge stimulators were also suggested by Villalobos et al. and the Bionic Vision Australia Group: They described a MEA which can be placed in the suprachoroidal space with dimensions of 8 × 13 mm, providing a visual angle in the human eye of about 27.14 × 39.8° or a visual field of 13.6 × 19.9°. MEA systems not in direct contact with the retina seemed to be limited in terms of spatial resolution because of the distance between the active electrodes and the target neurons. The advantage of suprachoroidal implants however might be the low risk profile of the surgery ,23.Studies on the safety of the EPIRET III device, which was also based on polyimide and contained similar materials and the same encapsulation as the VLARS prototypes confirmed a good biocompatibility and function of the implants –27]. Fo. Fo27]. The main concern for large stimulators is the possibility of intra- or postoperative complications. The larger incision necessary to implant such devices into an eye could cause a higher risk of infection, high astigmatism, leakage, and proliferative tissue reactions. Therefore, a flexible device is desirable which can be inserted through a smaller incision. Our experiments on enucleated pig and rabbit eyes showed that when using a nozzle the folded device could be inserted through an incision of 5-6 mm, which seems to be reasonable in terms of risk profile. Stimulation tests and impedance measurements on implanted devices are necessary to demonstrate that stimulators endure the implantation without any damage.Currently available epiretinal implants have certain drawbacks not only concerning their stimulator size but also concerning electrode size and material, and stimulation algorithms. To yield better spatial resolution a higher density of electrodes is desirable although that usually means to design smaller electrodes with a greater risk of adverse electrochemical reactions at their surface. Such electrochemical reactions have to be avoided by proper selection of the electrode surface material. Stimulation algorithms usually do not take into account that not only ganglion cells may be stimulated but also other excitable cells like amacrine cells or even bipolar cells . The actWe were able to demonstrate in a preliminary experiment, that the device is useful for electrical stimulation of the retina and that it also has the potential to record neural network activity. The latter allows the realization of bidirectional implants capable to record from the target tissue and to stimulate the tissue. The recordings could probably be used to automatically modify and optimize the stimulation pattern, which is usually based on image characteristics and fixed assumptions on the functional state of the retina.The successful fabrication of VLARS prototypes and the promising observations concerning surgical handling, stimulation and recording represent first steps in the realization of a large stimulating array for wide-field direct epiretinal stimulation to generate artificial vision with enlarged visual fields. Further experiments are necessary to demonstrate its long-term biocompatibility in-vivo and also its stimulation properties.The authors declare that they have no competing interests.FW performed the CAD design of the prototypes and simulated the mechanical properties of the VLARS MEAs and fabricated the prototypes under the supervision of WM. He wrote significant parts of the manuscript. SH did the recording and stimulation experiments with the VLARS MEAs and wrote the specific parts of the manuscript. ACR and TL prepared the surgical experiments and were responsible for the documentation. They did the literature search. CB and TLaube assisted in the surgical experiments and contributed extensively to the design concepts discussion and handling evaluation. NB, WM, GT, SJ, and PW developed the concept of VLARS MEAs, wrote the grant application, and wrote significant parts of the manuscript. They finally approved the paper. GR and GT performed the surgical handling tests and wrote the corresponding sections of the manuscript. All authors read and approved the final manuscript.


Tumor heterogeneity is well documented for many characters, including the production of growth factors, which improve tumor proliferation and promote resistance against apoptosis and against immune reaction. What maintains heterogeneity remains an open question that has implications for diagnosis and treatment. While it has been suggested that therapies targeting growth factors are robust against evolved resistance, current therapies against growth factors, like antiangiogenic drugs, are not effective in the long term, as resistant mutants can evolve and lead to relapse. We use evolutionary game theory to study the dynamics of the production of growth factors by monolayers of cancer cells and to understand the effect of therapies that target growth factors. The dynamics depend on the production cost of the growth factor, on its diffusion range and on the type of benefit it confers to the cells. Stable heterogeneity is a typical outcome of the dynamics, while a pure equilibrium of nonproducer cells is possible under certain conditions. Such pure equilibrium can be the goal of new anticancer therapies. We show that current therapies, instead, can be effective only if growth factors are almost completely eliminated and if the reduction is almost immediate. Heterogeneity of cells within a tumor is well documented for many types of cancers and many distinguishable phenotypes  secrete a growth factor. If the benefit of this factor is not restricted to the producers, we can consider it a public good that can be exploited by all other individuals (or cells) within the diffusion range of the factor, including nonproducers (−/−). Public goods are studied in economics, where rational, self-interested behavior may lead to the overexploitation of common pool resources [the ‘tragedy of the commons’ Hardin ], and inSimilar collective action problems arise during cancer development, where growth factors support tumor growth by protecting cells from apoptosis , by stimulating the growth of new blood vessels , by impairing immune system reaction , or by promoting the epithelial–mesenchimal transition. While cooperation for the production of growth factors has been shown directly only in one case (FGF) . The few exceptions /n] of the number j of producers among the other individuals (apart from self) in the group, normalized as b(j)=[V(j)-V(0)]/[V(n)-V(0)]. The parameter k controls the position of the inflection point (k→n gives strictly increasing returns and k→0 strictly diminishing returns) and the parameter s controls the steepness of the function at the inflection point  (Archetti and Scheuring A cell can be a producer (+/+) or a nonproducer (−/−) of a growth factor. Producers pay a cost c that nonproducers do not pay (0 < c < 1). All cells (+/+ and −/−) benefit from the public good produced by all the cells in their group . The benefit for an individual is given by the logistic function V(j)=1/[1 + ex is selected (at random) for update (death) and a cell y (with a payoff Py) is then chosen among x's neighbors. Two types of update are used: in the deterministic case, if Px > Py, no update occurs, while if Px < Py, x will adopt y's strategy ; in the stochastic case, replacement occurs with a probability given by (Py-Px)/M, where M ensures the proper normalization and is given by the maximum possible difference between the payoffs of x and y  connecting opposing edges to form a toroidal network, to avoid edge effects. As in the standard approach, individuals occupy the nodes of the network (population size is fixed at 900) and social interactions proceed along the edges connecting the nodes. Differently from the standard approach, however, [in which an individual's group is limited to her one-step neighbors and an individual plays multiple games centered on each of her neighbors  −b(j)where Δn = 25). In the standard approach, however, the focal individual contributes to all PGGs she is involved in, her one-step neighbors contribute to two PGGs that affect the focal individual, and her two-step neighbor contribute only to one PGG that affects the focal individual. In the case of diffusible factors instead, all individuals contribute equally to a single, larger PGG. Fig. A comparison between the standard framework and the one used here (decoupling interaction and replacement networks) is possible if we assume that d = 2 Fig. . Group sWhen a nonproducer (−/−) is introduced in a population of producers (+/+), in most cases −/− cells increase in frequency and coexist with +/+ cells; this change in frequency of the two types is accompanied by a change in the relative position of the +/+ and −/− cells, as shown by the degree centrality (the number of neighbors) and the closeness centrality  of the +/+ subgraphs Fig. . In mostBoth the frequency of producers and fitness at equilibrium decline with increasing d (the diffusion range of the public good), that is, increasing group size (n); −/− cells form clusters whose size increases with d Fig. . A shortThe stable equilibrium described above does not depend on the initial frequency of the two types Fig. , unless →0, the game approaches the N-person prisoner's dilemma (the benefit function is a linear function of the frequency of cooperators), and both internal equilibria disappear. Both the frequency of producers and fitness are higher at intermediate levels of h (the position of the threshold)  Fig. . A shallld) Fig. .As expected, increasing the cost of production (c) reduces both the frequency of producers and fitness at equilibrium Fig. . A critiAn anticancer therapy that acts by impairing circulating growth factors will increase the amount of growth factors that the cells must produce to achieve a certain benefit, that is, it will increase the threshold h. Two results are possible. In the first case, the population adapts to the new threshold, that is, +/+ cells increase in frequency and fitness increases - the opposite of the scope of the drug; only if the threshold increase is substantial does the +/+ type go extinct Fig. .The speed of the transition from the original to the new threshold is also essential for the success of a therapy that targets growth factors. While a fast transition to the new threshold can lead to a successful, stable therapy, a slower delivery can lead to relapse Fig. . In summThe logic of these two effects (magnitude and speed of the shift in threshold) can be understood by looking at the gradient of selection Fig. A. Note tIf the treatment is effective and fast enough that the population does reach the stable pure −/− equilibrium, a mutant +/+ will not be able to invade an infinitely large, well-mixed population. In a finite, structured population, however, it is possible that random fluctuations change the fraction of +/+ cells within a cluster above the unstable equilibrium, which would lead that cluster to the mixed equilibrium in which +/+ and −/− cells coexist Figs B and 11.Analyzing the production of growth factors as a nonlinear public goods game reveals that tumor heterogeneity can be maintained by the frequency-dependent selection that arises as a natural consequence of the fact that growth factors are diffusible, and therefore public goods. Tumor heterogeneity has important implications for diagnosis and treatment. The results help us understand anticancer therapies that attack growth factors, either directly (using drugs like Avastin that target the growth factors) or indirectly (using RNA interference). While it has been suggested that attacking growth factors may be less susceptible to the evolution of resistance Pepper , the resThe rationale of the analysis is that when one reduces the amount of a growth factor, the immediate result is a sudden reduction in tumor growth, because the threshold necessary to achieve the original benefit is not reached; as a consequence, the growth rate of the tumor immediately declines. At the same time, however, the amount of growth factors necessary for the population to grow increases (because part of them are disrupted by the drug), which changes the dynamics of the system; unfortunately, it changes into the wrong direction: by increasing the threshold, one increase the frequency of producers at equilibrium, which explains relapse simply as the new equilibrium reached by the system under the new conditions. While it is too early to evaluate the efficacy of RNAi treatments, it seems reasonable that even silencing the gene for a growth factor should incur a similar problem and be susceptible to the evolution of resistance.As pointed out by André and Godelle and PeppeAs we have shown, the details of the benefit function, diffusion range, cost of production, and update rule that drive the dynamics of growth factor production are critical to determine the type of dynamics and equilibria. More precise theoretical prediction therefore is necessary to understand under what conditions resistance will evolve, including the use of three-dimensional Voronoi graphs to model interactions within the tumor and gradients of diffusion to model the effect of growth factors. Furthermore, the results reported here only apply to growth factors that confer a direct advantage to the tumor, such as factors that protect against apoptosis and promote proliferation; other growth factors, however, act indirectly by inducing the production of other growth factors by stromal cells or by promoting the development of blood vessels. Finally, we have assumed competition due to constant population size, which may describe cancer cell populations that have reached a carrying capacity, but not early stages of tumor growth. Analyzing the dynamics of these cases requires more complex models.Understanding the production of growth factors as a public goods game suggests that an evolutionarily stable treatment could be achieved through autologous cell therapy Archetti : harvest


Therefore, in our opinion, the next step in research must be the isolated study of each of the main resistance exercises. Since the literature is scarce and that we do consider that the majority of the studies present severe limitations, the aim of this paper is to present a critical analysis of the energy cost estimation methods and provide some insights that may help to improve knowledge on resistance exercise. It seems necessary to rely on the expired O2 measurements to quantify aerobic energy. However, it is warranted further attention on how this measure is performed during resistance exercises. In example, studies on the O2 on-kinetics at various conditions are warranted . As for anaerobic lactic energy, it is our opinion that both the accumulated oxygen deficit and the blood lactate energy equivalent deserve further studies; analyzing variations of each method as an attempt to establish which is more valid for resistance exercise. The quantification of alactic anaerobic energy should be complemented by accurate studies on the muscle mass involved in the different resistance exercises. From the above, it is concluded that knowledge on the energy cost in resistance exercises is in its early days and that much research is warranted before appropriate reference values may be proposed.The use of resistance exercises and of typical strength training methods have been progressively used to control body mass and to promote fat mass loss. The difficulties involved in the energy cost calculation during strength training are associated with the large amount of exercises and their several variations. Mean values between ≈3 and 30 kcal·min Physical activity by the use of resistance exercise (RE) is a common modern trend. This trend is not limited to high-performance athletes, but also in physical rehabilitation programs and in physical activity with aesthetical or health-promotion purposes. As a sign of times, the American College of Sports Medicine  recommen−1 in men  during and post-exercise, the accumulated oxygen deficit during exercise and the blood lactate post-exercise.The large variability of the values presented above, turns research almost obsolete in terms of being able to predict with an acceptable error which is the EE in a standard session of ST. In our opinion, the next step in ST research should be the isolated study of the main resistance exercises. Being able to identify the bioenergetics in each exercise and the way it varies with its different variations or in different populations, will improve the design of ST programs. In cases where the aim of the ST is to promote body mass loss or fat mass loss, the choice of exercises, loads, recovery periods, total training volume (and other characteristics of a training session) should be done according to the knowledge of the EC of each and every exercise that is used. Indeed, the bioenergetics of RE is little known, especially in what concerns the quantification of the EC in isolated exercises , and areConsidering the scarcity of studies and the fact that we do consider that the majority of the studies present severe limitations, the aim of the present paper is to present a critical analysis of the methods that are typically used to quantify the EC and to propose some new insights suitable to improve knowledge about RE and ST.2 measurement and only when the anaerobic energy involved in the exercise is negligible, it is licit to consider that the EE is truly measured. So, we have already a first and severe limitation to use this concept in ST, as RE are typically characterized by a significant anaerobic energy release. For these reasons we prefer to refer to the concept of energy cost (EC). The EC represents the total amount of energy that is necessary to perform an exercise and it includes the two fractions of energy, both aerobic and anaerobic. The aerobic fraction can be directly measured without error  through the VO2 measurement; and the anaerobic fraction can only be estimated. The latter, being estimated, it involves necessarily a certain amount of error adding to the technological error associated with the equipments and techniques of measurement.The reader may notice that in the past section we have referred two concepts: energy cost (EC) and energy expenditure (EE). We will explain the rationale behind the separate concepts. We chose to use EE when the methods that are used allow a direct quantification and with no measurement error. The measurement error herein is limited to the technological error with the use of gold-standard equipments and techniques; that is, very low. As such, only when the aerobic fraction of energy release is assessed with VO2 measurements are only a part of the total energy demand . Moreover, it is also important to remind the reader that even VO2 measurements, when performed during recovery periods (between exercises or post-session) do not quantify with precision the aerobic energy release. In fact, during post-exercise periods, the VO2 represents several mechanisms that the human body uses to reestablish its homeostasis. Hence, post-exercise VO2 does not quantifies the energy demand (energy cost) of any given exercise.This separation can be considered conceptual or even merely operational. If the reader prefers, merely operational so be. We do not disregard the use of EE, but it is important to draw attention to the fact that VOTherefore, we consider the EC concept to be more precise and more suitable to be used. In the present paper, we will only use this concept from now on.2 content in expired gases during exercise. The respiratory exchange ratio (R) is the expression of the respiratory quotient in the ventilation and can also be measured in the expired gases. The R may serve to estimate the relative substrate oxidation . On the other hand, for each R value there is an energy equivalent by liter of O2 uptake. In example, the energy equivalent for R=0,7 is 4,69 kcal·L−1 O2; for R=0,8 is 4,80 kcal·L−1 O2; and for R=1,0 it is 5,05 kcal·L−1 O2 .Aerobic EC is usually assessed by indirect calorimetric, with the measurement of the VOxidation  in the ml·L−1 O2 . At rest2 as a quantitative measure of EC and the use of R as an indicator of the appropriate energy equivalent assumes that gas exchanges are measured during a metabolic equilibrium state (when there is a steady-state VO2 in the mouth). In practical terms, this means that the assessment of the aerobic energy cost is more valid the lower the exercise intensity and the higher the exercise duration. Grossly, one may consider as valid the following conditions of exercise: i) exercise intensities below that corresponding to the lactate threshold (LT) and a duration above 3-min; ii) exercise intensities comprised between that corresponding to the LT and that corresponding to the maximal VO2 and a duration above 5-min (or a duration that is necessary to attain a steady-state).The use of VO2 kinetics is well described as a function of the intensity and the duration of exertion. However, this is not the case with RE. On the other hand, the intensity which corresponds to the start of an exponential and fast accumulation of lactate in the blood is also scarcely analyzed. Indeed, the lactate threshold (LT) in the blood, identified as being somewhere between 70 and 80% of maximal VO2 in running or cycling exercise, it is not that well established during RE. Some exploratory data found LT to be around 30% 1-RM , for a total EC of 4,7 kcal·min−1 (−1). In the latter study it is not possible to conclude how much was the aerobic EC but it is likely to be higher compared to that reported by The few studies about the aerobic EC in isolated resistance exercises show that in the bench press it can be as low as 1,5 kcal·minal·min−1 . Robergs−1 at low intensities (from 12 to 24% 1-RM). In these same 3 exercises performed at 80% 1-RM, the total EC varied between 10 and 12 kcal·min−1, with 22 to 36% released from anaerobic sources . Our data suggest that at intensities below 30% 1-RM the energy may be almost fully aerobic (disregarding that from the O2 stores which are included in the early O2 deficit) and that at higher loads the CE may increase concomitantly to the increases in the anaerobic energy release . This hypothesis is yet to prove and only careful analysis on the VO2 kinetics, may confirm the negligible anaerobic contribution at low workloads (up to 30% 1-RM). In the ½ squat we found much different estimations. The total EC at lower intensities (from 12 to 24% 1-RM) varied between 10 and 12 kcal·min−1, but at 80% 1-RM attained 40 kcal·min−1, with no more than ≈6 kcal·min−1 from aerobic sources (other than the O2 stores). The variability of the data  and the imprecision of the EC (standard error of the regression between VO2 and workload) were larger in this exercise, compared to those previously identified. Although we did not analyzed the VO2 on-kinetics with multi exponential modeling, in the ½ squat an apparent slow component was present at intensities below 30% 1-RM (as shown by a difference between end VO2 and 2nd minute VO2 higher than 300 ml·min−1).Our preliminary results (unpublished data) with recreational resistance-trained men, show that in bench press, triceps extension and latt pull down, the total EC is almost similar and calculated to be around 3 to 5 kcal·minThe methods which are typically used to assess the anaerobic EC are less precise compared to those assessing aerobic EC. A variety of indirect methods have been used, but none of them is indisputably accepted as the most accurate. The gold standard method to asses alactic and lactic anaerobic energy release would warrant muscle biopsy, thereby allowing the quantification of the energy sources inside the muscle cell (i.e. high-energy phosphates and glycogen) as well as an accurate measure of metabolite accumulation in the muscle (i.e. muscle lactate). A limitation of this technique is due to the fact that only a minor portion of the human muscle tissue may be submitted to a biopsy. Moreover, it may be necessary to obtain several samples of tissue located at different depths to attain a sample that is representative of the muscle  and that2 on-response during exercise and according to 2·kg−1. The pioneer studies by 2 kg−1·mM−1). It is a fact that di Prampero clearly stated that this equivalent does not represents an energy equivalent of lactate formation, rather representing an amount of energy that could be attributed to the lactic metabolism when the rate of lactate formation greatly surpasses that of its elimination (M threshold), that it may be unnecessary to include such measurements to estimate the total energy cost of exercise. The rationale behind this idea is quite simple and straightforward. The blood lactate values above that of resting conditions during sub maximal exercise are probably due to an initial lactate formation  accumulation post-exercise. Usually this measure is completed with an assumption of the alactic energy sources, with a value that may vary with exercise and that is often estimated by the temporal constant of the fast Omination . As suchormation . Subsequture ex. , in our ture ex. ; 2011.2 measurement and allows the quantification of the aerobic and anaerobic fraction of energy release in relation to the overall EC. This method, rarely used in RE . This is a measure which includes the two components and that does not require invasive techniques. The AOD determination is possible from VOed in RE  has beened in RE , cyclinged in RE  and moreed in RE a,b and ied in RE . As with−1. In a previous study , when compared with women . Recently, −1 at 60% and it was 1 kcal·min−1 at 80% 1-RM in women; and it was 6 kcal·min−1 at 60% and 3 kcal·min−1 at 80% 1-RM in men. Finally, in leg press anaerobic EC was up to 3 kcal·min−1 in women and it was 9 to 10 kcal·min−1 . It is worthwhile to mention that none of these estimations added the contribution of the alactic energy to the anaerobic energy cost.The studies on the BL energy equivalent during isolated RE are limited to bench press, leg press and biceps curl exercises ; 2011. Sus study  the auth−1, representing from 65 to 80% of total energy release (unpublished data). In the ½ squat at the same relative intensity, we found a mean anaerobic fraction ≈80% with an EC from anaerobic sources up to 36 kcal·min−1. According to our results, the AOD during RE may attain values close to 50 ml· kg−1min−1 in a 30 s duration, which represents a rate of anaerobic energy release higher than that described for maximal intensity running or cycling.Using the AOD method to assess the EC in RE, our data with trained men suggest that in bench press, triceps extension and latt pull down the anaerobic EC is 7 to 10 kcal·min2 measurements to assess the aerobic EC during RE. However, further research is warranted to improve the interpretation of this measure . The post-exercise VO2 measurement may be of interest only in the case of comparative studies and when full sessions of ST are to be analyzed, but not in the bioenergetics characterization of isolated RE; since this measure includes both aerobic and anaerobic metabolisms and it also involves homeostasis mechanisms which do not reflect quantitatively the energy demand during exercise.In summary it seems to be quite clear that it is necessary to rely on expired O2 on-kinetics (O2 deficit) and off-kinetics (O2 debt). However, this approach ought to be complemented with concomitant studies aiming to quantify more precisely the amount of muscle mass involved in each RE exercise . To date, the available studies show that:The EC in RE at the intensities often used in training is predominantly anaerobic.The rate of anaerobic energy release in exercises such as squatting may be higher than maximal values described for high-intensity running or cycling.vs. AOD). This mismatch may indicate that the lactate energy equivalent from running, cycling and swimming studies may not be applicable to RE.The anaerobic EC seem to present different estimations according to the different methods  implies a wide range of possible studies. However, the next step in the evolution of the state-of-the-art should comprise methodological analysis able to demonstrate which methods, techniques and procedures are to be recommended in this line of research.


This is important because there is evidence for perception of derived patterns in the binocular rivalry experiments of Kovács, Papathomas, Yang, and Fehér. We construct modified Wilson networks for these experiments and use symmetry breaking to make predictions regarding states that a subject might perceive. Specifically, we modify the networks to include lateral coupling, which is inspired by the known structure of the primary visual cortex. The modified network models make expected the surprising outcomes observed in these experiments.Binocular rivalry is the alternation in visual perception that can occur when the two eyes are presented with different images. Wilson proposed a class of neuronal network models that generalize rivalry to multiple competing patterns. The networks are assumed to have learned several patterns, and rivalry is identified with time periodic states that have periods of dominance of different patterns. Here, we show that these networks can also support patterns that were not learned, which we call  Wilson  argues tillusions due to insufficient information and rivalry due to inconsistent information. One of the standard examples of illusion is given by the Necker Cube shown in Fig. perceived when viewing the Necker cube picture: one with the yellow face at the back and one with it on top. There is not enough information in the picture to fix the percept and this ambiguity leads to the two percepts alternating randomly. We begin by making a distinction between two types of perceptual alternations (Blake and Logothetis ): illusiIn rivalry, the two eyes of the subject are presented with two different images such as the ones in Fig. a and b corresponding to the two percepts with a system of differential equations of the form The simplest deterministic version of the first type, studied by many authors including ,10-18, aa and the vector b. The equations in (1) are those associated with the two-node network in Fig. activity variable and that a is dominant. Similarly, percept b is dominant if winner-take-all states that correspond to one percept being dominant.  where the vector fusion states. Fusion states are typically interpreted as states where a subject perceives both of the images superimposed [States where rimposed -20. One Periodic solutions representing rivalry are most easily found in model equations (1) by using symmetry-breaking Hopf bifurcation from a fusion state. Note that the symmetry in (1) is given by permuting the two units. In such systems, there are two types of Hopf bifurcation: symmetry-preserving and symmetry-breaking. The two types are distinguished by which subspace T is the period. Such solutions lead to periodic alternation between percepts a and b; that is, to rivalrous solutions. contains the critical eigenvectors at Hopf bifurcation. Symmetry implies that generically the critical eigenvectors are either in one subspace or the other . Symmetrinterocular grouping, had been documented previously , and haz-Coneja ). Of thez-Coneja , only thcolored dot rivalry experiments that are analogous to the conventional and scrambled monkey-text experiments. In the conventional colored dot experiment, the subjects were shown the single-color images in Fig. monkey-text experiment seems highly unlikely. Kovács et al.  also discolored dot experiment, [monkey-text experiment, it is not surprising that subjects reported rivalry between these two scrambled color images and also rivalry between single color images such as shown in Fig. colored dot experiment with the scrambled monkey-text experiment is not quite so straightforward, since, as we will see in Sect. 2, the proposed Wilson networks for the two experiments have different symmetries.In the scrambled eriment,  presentecolored dot experiments of [Tong, Meng, and Blake  give a sments of  by usingThe purpose of this paper is to show that all of the surprising observations made in the four rivalry experiments reported by  can be umonkey-text experiment is the standard two-node rivalry model in Fig. monkey and the whole text images.(1) The simplest Wilson model for the conventional monkey-text experiment leads naturally to rivalry solutions between the scrambled images and also between the reconstructed images.(2) The simplest Wilson model for the scrambled colored dot experiment also leads naturally to rivalry solutions between both the scrambled and the reconstructed images.(3) The modified Wilson model for the scrambled colored dot experiment leads naturally to rivalry between scrambled images as well as to between the conventional images. This is in contrast to the conventional monkey-text experiment.(4) The Wilson model for the conventional colored dot experiments and these states may be thought of as predictions made by our approach.We will see that our analysis also leads to possible additional rivalry states in the derived; the derived patterns are the ones that correspond to the unexpected results in the Kovács et al. experiments. Second, we introduce an additional type of coupling, lateral coupling, based on models of hypercolumns in the primary visual cortex literature . monkey-text experiment are always unstable. However, stability is a model-dependent property of solutions and simple changes to the network or to the model equations can lead to stable derived patterns.Deciding on the exact form of a Wilson network model for a given experiment is not at this stage algorithmic. Moreover, there are many choices for the exact form of the network equations once the network is fixed. If we take the strict form of the Wilson models  and we assume that the associated differential equations are highly idealized rate models (as Wilson does), then the derived patterns in the colored dot experiments by a change in network symmetry. The most important message in this paper is the observation that Wilson networks have derived patterns that can be classified using methods from the theory of symmetry-breaking Hopf bifurcations and that these derived patterns appear to correspond to the surprising perceived states found in psychophysics experiments. More discussion is needed to arrive at an algorithmic description of which (modified) Wilson network to use when modeling a given experiment.There are many ways to modify Wilson networks to address the stability issue and we have chosen one here, namely, we have added lateral coupling to the network. Lateral coupling will also enable us to distinguish the Wilson network models for the two colored dot experiments is based on the four-dot version in [Section 3 gives a brief description of equivariant Hopf bifurcation  and shorsion in  and on H Stewart ) and of y et al. ). Note tmonkey-text networks. In this section, we use standard rate models to compute stability and to illustrate the effect of having lateral coupling.Section 4 summarizes the calculations needed to compute stability for rivalrous solutions between both learned and derived patterns in the scrambled model independent one advocated in Golubitsky and Stewart [model dependent. Our discussion of stability in Sect. 4 does rely on the choice of specific model equations; here we use the rate models introduced by others.We end this Introduction by emphasizing that our approach is mainly a  Stewart . We use  Stewart ,10,11,28Wilson networks  are assupattern is a choice of a single level in each column. If the network has learned a particular pattern, then there are reciprocal excitatory connections between all nodes in the pattern. See Fig. A pattern is defined by the choice of levels of a set of attributes. Specifically, Wilson networks consist of a rectangular set of nodes, arranged in columns, and two types of coupling. The columns represent attributes of an object and the rows represent possible levels of each attribute. There are reciprocal inhibitory connections between all nodes in each column. See Fig. lateral coupling that connects neurons in neighboring hypercolumns [Before discussing networks for the rivalry experiments in , we consrcolumns ,29. Morercolumns ,30, albesame level. See Fig. With the structure of V1 as inspiration, we define an excitatory lateral coupling in the Wilson networks by connecting those nodes in different columns that correspond to the monkey-text experiment can be modeled by a two-level, two-attribute Wilson network with two learned patterns. To specify the network, we conceptualize the Kovács images in Fig. monkey image in the associated region and the portion of the text image in that region. The scrambled i of attribute j as shown in Fig. monkey in the white region in Fig. text in the white region. Similarly, monkey in the blue region and text in the blue region. Thus, there are reciprocal inhibitory connections between nodes monkey only image in Fig. text only image in Fig. This network has four nodes, where Note that lateral coupling changes the network in Fig. colored dot experiment as shown in Fig. The symmetries of the networks in Fig. colored dot experiments in [colored dot experiment, one learned pattern has four red dots and the other has four green dots, as shown in Fig. Tong et al.  suggest ments in , where eWe model this experiment by a Wilson network consisting of four attribute columns, where each attribute refers to the position of one of the dots  and has two levels (red and green). The eight-node Wilson network with two learned patterns is shown in Fig. colored dot experiment is shown in Fig. colored dot experiments, which is not what is observed. The Wilson network with lateral coupling for the scrambled Wilson networks have symmetry and these symmetries dictate the kinds of periodic solutions that can be obtained through Hopf bifurcation from a fusion state. The classification of periodic solutions proceeds as follows. See . Γ of the network and how Γ acts on phase space.(1) Determine the symmetry group Γ. (2) Determine the irreducible representations of this action of (3) Classify the periodic solutions for each distinct irreducible representation by their spatiotemporal symmetries.Γ. An isotypic component consists of the sum of all isomorphic irreducible representations. In general, step 3 is difficult, but it has been worked out in the literature for most standard group actions. Note that if a symmetry ρ be the symmetry that transposes the two nodes in each column. A solution that is invariant under ρ will have activity variables equal in each column and, therefore, be fusion states. Step 1 is straightforward for the networks we consider. Step 2 is most easily determined by computing the isotypic decomposition of The form of equations relevant to the network in Fig. X is the internal state variable of the given node, Y is the node connected to X with inhibitory coupling, and Z is the node connected to X with excitatory learned pattern coupling. Note that for general networks  where in ρ that swaps rows and the symmetry κ that swaps columns. Specifically, We claim that two types of non-fusion oscillation can be obtained by Hopf bifurcation from fusion states , is block diagonalized by the isotypic decomposition of the symmetry group acting on phase space . The isotypic decomposition for  where the ρ satisfies X where all ρ fixes all points in the isotypic component) lead to rivalry between fusion states. where The Wilson network in Fig. (Stewart  and Dias(Stewart ). Equivariant Hopf bifurcation is driven by the irreducible representations of Γ acting on  It follows that the irreducible representations of colored dot network of the decomposition (4) for the scrambled monkey-text network. Note that ρ acts trivially in the plus representations and as multiplication by −1 in the minus representations. All solutions bifurcating from a plus representation are invariant under ρ, and hence are fusion states, since invariance under ρ implies that the entries in each attribute column are equal. The decomposition (5) is the analog for the conventional On the other hand, all periodic solutions bifurcating from a minus representation satisfy T-periodic. Hopf bifurcation based on  We use the notation Next, we consider Hopf bifurcation based on lyzed in . (The stlyzed in .) Up to colored dot experiment with a n dots. Then there will be n attribute columns with a symmetry group We have focused on the simplified version of the conventional Γ acting on  It follows that the irreducible representations of n dots is analogous to that of 4 dots; there are two types of bifurcation to fusion states  emphasizes the fact that there are three different types of coupling: inhibitory, excitatory learned, and excitatory lateral.The isotypic decomposition of Γ acting on  It follows that the isotypic components of  As in the previous examples, bifurcation with respect to Finally, we note that the discussion in this section generalizes to the scrambled dot experiment with a Γ-equivariant. Given a system of equations, we can prove that solutions of the types that we have classified actually exist only by showing that a Hopf bifurcation that corresponds to the appropriate isotypic component actually occurs. See the equivariant Hopf theorem in [The classification of possible solution types, as given in Sect. 3, is model independent. We do not need to know the particular equations in order to complete the classification; we just need to know that the equations are eorem in . We can J at the fusion equilibium correspond to the given isotypic component and all other eigenvalues of J have negative real part. Third, we need to calculate higher order terms in a center manifold reduction to check that the bifurcating solutions are actually stable. Alternatively, we can just simulate the equations for parameter values near a stable Hopf point and see whether we can detect stable solutions. Indeed, this was our approach for the scrambled monkey-text model in Sect. 2.There are three steps in the calculation of stability. First, we need to determine that there is a fusion equilibrium. Second, we must show that the Hopf bifurcations themselves can be stable. That is, we must find Hopf bifurcation points where the critical eigenvectors of the Jacobian The principal conclusion is that derived pattern rivalry (between unscrambled images) can be stable in this model only if the strength of the lateral coupling is greater than the strength of the learned pattern coupling (see Proposition 3). Note that this cannot happen if lateral coupling is absent. We also show that learned pattern rivalry (between scrambled images) can only be stable when the strength of the learned pattern coupling is greater than the strength of the lateral coupling (see Proposition 2).There is some leeway in choosing differential equations associated to a given network. In this context, we follow Wilson and others and assume that the nodes are neurons or groups of neurons and that the important information is captured by the firing rate of the neurons. Thus, we follow  and assu where → indicates an excitatory learned pattern connection, ↦ indicates an excitatory lateral connection, and ⇒ indicates an inhibitory connection. Similar rate models are often used in the rivalry literature . TheIn this case, we assume all monkey-text experiment. The additional coupling allows the rivalrous solutions with respect to the derived patterns to be asymptotically stable at bifurcation; these solutions are not stable if lateral coupling is excluded.As we will see, there is an advantage of lateral coupling in the four-node model for the scrambled The equations for a fusion equilibrium for (11) reduces to  where all udied by ,11,34. I Then (12) can be rephrased as ρ there is an w, δ, β, g, ε. We are particularly interested in the case when  Diekman et al. (Lemma 3.1 in ) state tLemma 1FixFixso that theThen there exists a gain functionsatisfyingandIt follows from Lemma 1 that Proof of Lemma 1 The sigmoidal function a equal to the RHS of (14), which is also positive since ρ and  satisfies For Hopf bifurcation to exist, we need one trace to be zero and the corresponding determinant to be positive. For that Hopf bifurcation to be stable, we require all four determinants to be positive and the remaining three traces to be negative.Proposition 2To have stable Hopf bifurcation to learned pattern rivalry in (11), it is necessary thatSufficient conditions for stable Hopf bifurcation to learned pattern rivalry are given by (18) andProof For Hopf bifurcation to learned pattern rivalry to exist, we need ε in (17), we obtain the necessary conditions  It follows from (19) that  Note that the necessary conditions (18) follow from directly from (20) and the second condition in (20) follows from the first and third.To prove the sufficiency part of the lemma, we need to verify that the determinants are all positive. This follows from (16) if  Note that the second inequality is always satisfied and, assuming (18), the first and third follow from the fourth. Finally, the fourth inequality follows from (19). □Note that Hopf bifurcation to stable learned patterns is possible when the lateral coupling is nonexistent; that is, Proposition 3To have stable Hopf bifurcation to learned pattern rivalry in (11), it is necessary thatSufficient conditions for stable Hopf bifurcation to learned pattern rivalry are given by (22) andProof For Hopf bifurcation to derived pattern rivalry, we need ε in (17), we obtain the necessary conditions:  It follows from (23) that  Note that the necessary conditions (22) follow directly from (24) and the second condition in (24) follows from the first and third.To prove the sufficiency part of the lemma, we need to verify that the determinants are all positive. This follows from (16) if the four conditions (21) are satisfied. Note that the second inequality is always satisfied and, assuming (22), the first and fourth follow from the third. Finally, the third inequality follows from (23). □Note that Hopf bifurcation to stable derived patterns is possible only when the strength of the lateral coupling is larger than the strength of the learned pattern coupling; that is, We have shown that the surprising results in three binocular rivalry experiments described by Kovács et al.  can be uWe would like to put our results in a broader context. We showed in Diekman et al.  that rivthis way . This sucolored dot experiments, we assume that the attributes are the colors of the dots at four geometric locations. On the other hand, in the scrambled monkey-text experiment, we assume that the attributes are the kind of picture (monkey or text) in two regions of the image rectangle  and the quotient networks from coupled cell theory [ (see ) that isl theory . eye-based theories postulate that the two eyes compete for dominance, while stimulus-based theories postulate that it is coherent perceptual representations that are in competition . Kovácss et al.  interpremonkey-text images and an eye-swap technique that exchanges rival images immediately after one becomes dominant . In thee et al.  considercolored dot experiments. We also note that illusions are part of this network theory and they themselves can lead to interesting kinds of perceptual alternations. This topic, as well as symmetry-breaking steady-state bifurcations that lead to various types of winner-take-all states, will be discussed in future work.We end by noting that it should be possible to test our predictions of likely percepts by performing the simplified The authors declare that they have no competing interests.All authors performed research. COD and MG drafted the manuscript. All authors read and approved the final manuscript.


Crohn’s disease is the most frequent inflammatory bowel disease. The use of the TNFα inhibitors has completely revolutionized the therapeutical management of recalcitrant cases of Crohn’s disease . UnfortuWe report a case of a young woman suffering from Crohn’s disease since 2001. She was treated by infliximab at the dose of 5 mg/kg every 8 weeks since 2009.She developed in 2011 an extensive lichenoid eruption in her arms and legs [Figure Skin biopsies were performed and showed an histological picture of lupus. Six weeks after the withdrawal of the infliximab therapy the skin lesions were completely healed and the anemia was resolved. A diagnosis of a lupus like syndrome induced by the infliximab was retained.Despite the frequent induction of autoantibody production in patients treated with TNFα inhibitors, the development of lupus like syndrome is uncommon, with a prevalence of 0.5% to 1%. The most cases have been described after the use of infliximab. The skin involvement is rare and the arthralgia are most frequent [Through the presentation of this case report, we wanted to discuss the role of this autoantibodies and their association with pathological conditions. We wanted also to focuse about the management of the lupus like syndrome induced by the TNFα inhibitors.