Recent years have witnessed a spurt of progress in the application of the encoding and decoding of neural activities to drug screening, diseases diagnosis, and brain–computer interactions. To overcome the constraints of the complexity of the brain and the ethical considerations of in vivo research, neural chip platforms integrating microfluidic devices and microelectrode arrays have been raised, which can not only customize growth paths for neurons in vitro but also monitor and modulate the specialized neural networks grown on chips. Therefore, this article reviews the developmental history of chip platforms integrating microfluidic devices and microelectrode arrays. First, we review the design and application of advanced microelectrode arrays and microfluidic devices. After, we introduce the fabrication process of neural chip platforms. Finally, we highlight the recent progress on this type of chip platform as a research tool in the field of brain science and neuroscience, focusing on neuropharmacology, neurological diseases, and simplified brain models. This is a detailed and comprehensive review of neural chip platforms. This work aims to fulfill the following three goals: (1) summarize the latest design patterns and fabrication schemes of such platforms, providing a reference for the development of other new platforms; (2) generalize several important applications of chip platforms in the field of neurology, which will attract the attention of scientists in the field; and (3) propose the developmental direction of neural chip platforms integrating microfluidic devices and microelectrode arrays. The brain is the most complex organ in human beings and the most sophisticated structure of nature. It is composed of hundreds of billions of neurons and their interconnected networks . The comThe development of in vitro MEAs aims to explore the potential mechanism of production, processing, and transmission of neural information in the brain . In vitrAlthough the neural chip platform containing only in vitro MEAs can cultivate 2D ,21 or 3DThe purpose of this review is to discuss the latest trends in neural chip platforms integrating microfluidic devices and microelectrode arrays. For our purpose, we divided this article into three parts: First, the latest research progress on MEAs and microfluidic devices in the field of neural science is introduced, and the design and fabrication of microelectrode arrays and microfluidic devices are introduced. Next, we describe the latest developments on microfluidic and microelectrode array neural chip platforms from three popular application fields, namely, neuropharmacology, neural diseases, and simplified brain models. Finally, we put forward the development direction of the platform. A schematic diagram of this overview is shown in Generally, microelectrodes, with diameters ranging from several microns to tens of microns, are patterned and arranged onto flexible or rigid substrates to produce MEAs by semiconductor micromachining technology. The MEA has both neural recording and modulation functions, among which neural modulation refers to the electrical stimulation of neuron cells through microelectrodes. Due to the small-sized feature of microelectrodes, MEAs can detect neural information with a high time–space resolution. The MEA can not only detect the local field potential (LFP) generated by multiple neuron activities but can also accurately record the action potential of a single neuron ,31. TherMEAs can be divided into implantable MEAs  and in vThe traditional structure of MEAs consists of a base layer, a conductive layer, and an insulating layer. The base layer is used to hold conductive and insulating materials. The metal layer includes electrode sites, a connecting wire, and contact sites for an external circuit for recording and transmitting neural activity. The insulating layer is used to protect the conductive structure that does not contact with neural cells.The MEA detects the electrophysiological activity of neural cells through the electrode interface in contact with neural cells. The ideal electrode should have the ability of high time–space resolution detection due to the low impedance, small phase delay, and a high signal-to-noise ratio as well as the ability of precise and safe electrical stimulation due to a high charge injection density and a high maximum charge safe injection limit. These properties depend on the material and structure of the conductive layer. However, Pt, Au, ITO, TiN , and oth2 particles have a certain neurotoxicity through cortical networks . T. T98]. TFinally, we used Neural chip platforms integrating microfluidic devices and microelectrode arrays have developed rapidly over the past decade. Compartmentalized microfluidic devices facilitate the control of the morphology of the neural network as well as the microbiochemical environment. Meanwhile, microelectrode arrays can feedback the changes in the neuronal network activity by detecting the electrophysiological signals networks. Overall, neural chips integrating microfluidic devices and microelectrode arrays have been developed into highly promising platforms for practical use, e.g., in vitro drug screening, mechanistic studies of neurological diseases, simplified model studies of the brain, etc. The neural chip platform has shown excellent application potential in neural correlation, and researchers have shown increased interest. Therefore, we comprehensively reviewed and focused on recent advances in the application of neural chip platforms.Despite the exciting progress of neural chip platforms in neural fields, there are still many challenges. Below, we summarize several of the current major pitfalls of neural chip platforms. First, the space and maintenance of cell growth substances for cultures in microchambers and microchannels are greatly reduced compared to cultures exposed directly to air. This challenges the ability of cells to maintain long-term good activity  and greaIn the future, researchers can make efforts in many directions to further optimize neural chip platforms integrating microfluidic devices and microelectrode arrays. First, the long-term cell culture technology in microfluidic devices can be further improved. For example, an automatic delivery system adding culture medium can be included in microfluidic devices, turning the cells in the microchannel into rich nutrients. In addition, improvements to the spatial structure of microfluidic devices can be an effective method. In studies of microelectrode arrays integrated microfluidic devices, the culture cycle of neural cells is usually less than two months ,61,154.


Screening initiatives were mostly shown to be cost-effective compared to non-screening. However, inter-study comparisons remained ambiguous due to large variations. The observational and randomized controlled trials provided considerably accurate evidence of implementation costs and outcomes. Modeling approaches, conversely, appeared more feasible for the estimation of long-term consequences and the exploration of strategy options. The current evidence of the cost-effectiveness of oral cancer screening remains heterogeneous and inadequate to support its institutionalization. Nevertheless, evaluations incorporating modeling methods may provide a practical and robust solution.A lack of guidance on economic evaluations for oral cancer screening programs forms a challenge for policymakers and researchers to fill the knowledge gap on their cost-effectiveness. This systematic review thus aims to compare the outcomes and design of such evaluations. A search for economic evaluations of oral cancer screening was performed on Medline, CINAHL, Cochrane, PubMed, health technology assessment databases, and EBSCO Open Dissertations. The quality of studies was appraised using QHES and the Philips Checklist. Data abstraction was based on reported outcomes and study design characteristics. Of the 362 studies identified, 28 were evaluated for eligibility. The final six studies reviewed consisted of modeling approaches ( Oral cancer has always been a significant disease burden worldwide. In 2020 alone, 377,713 new cases and 177,757 deaths were due to lip and oral cancer ,5.One of the reasons postulated for the plateau and poorer outcomes was the delay in early detection, leading to diagnosis in later stages. Relative to other cancers, oral cancers are often preceded by visible and abnormal lesions, known as oral potentially malignant disorders (OPMD). They consist of a wide range of disorders such as oral leukoplakia, erythroplakia, submucous fibrosis, and lichen planus. These lesions have variable chances of progressing into neoplasms, ranging from as low as 5% to as high as 85% . AlthougEarly screenings have thus been promoted as being an integral part of national control programs . StudiesCurrent recommendations often cite randomized controlled trials (RCT) as the gold standard in healthcare economic evaluations. However, adopting such a design in oral cancer screening can be challenging due to its pathophysiology and latency. Alternatively, modeling approaches have recently been advocated as a more feasible solution in many cancer screening programs, including oral cancer . SeveralA systematic review is widely acknowledged as an essential approach to informing decision-makers and researchers about the best practices and policies. The methodological differences between the modeling approach and trial-based economic evaluations limit the comparability of recommendations while necessitating the evaluation of the methodologies separately. This includes the application of different quality assessment tools and the interpretation of findings. For these reasons, this systematic review aims to summarize the outcomes and compare the design of economic evaluations on oral cancer screening to guide future study development.The initial search for this systematic review was conducted on four major databases: Medline, CINAHL, Cochrane, and PUBMED; two databases for health technology assessment: the Centre for Reviews and Dissemination of the University of York and the International Network of Agencies for Health Technology Assessment (INAHTA); and relevant theses in EBSCO Open Dissertations. Appropriate Medical Subject Headings (MeSH), thesauruses, and specific keywords were combined using Boolean operators in search terms and guided by the criteria in Examples of search terms are attached in Titles and abstracts were first scrutinized by a reviewer (S.R.) based on relevance. The full text of selected studies was later obtained and reviewed independently by two reviewers (S.R. and B.Y.). There were no restrictions in terms of the population characteristics, patient recruitment methods, study design, or implementation of strategies to ensure a comprehensive review. Studies were only excluded if (1) the full text was unavailable, (2) there was no or a partial economic evaluation, (3) screening consisted of other than visual oral examinations, and (4) it was not an original article. At this stage, excluded studies were listed, and the reason for exclusion was reported. Any discrepancy in the selection of papers was discussed between the reviewers until a mutual agreement was reached.Studies were first ranked by both reviewers according to quality scores using the broad Quality of Health Economic Studies (QHES) checklist. The list consists of 16 items of varying importance . AdditioData were extracted into three major sections to aid discussions: (1) study characteristics, (2) reported outcomes, and (3) model design. A standardized data extraction form was developed in Microsoft Excel based on literature and expert review . The extEvaluations that piggybacked on top of clinical studies were labeled as trial-based economic evaluations. On the other hand, model-based evaluations consisted of any studies combining a variety of source data via an economic model . This ron = 22) is available in n = 3) not fulfilled. The reduced quality score for Van der Meij et al. [The initial search yielded 362 papers. After the removal of duplicates and irrelevant studies, the remaining 28 studies were assessed for eligibility. A total of six studies were included in the final review see . A detaij et al.  was partn = 4), randomized controlled trial (n = 1), and retrospective observational study (n = 1). The studies predominantly explored the impact of the initiation of oral cancer screening in populations aged between 35 and 40 years. While Van der Meij, et al. [Study design, screening strategies, and outcome measures are summarized in , et al.  began th, et al.  reported, et al. ,18.n = 4), followed by targetted screening (n = 2), and opportunistic screening (n = 1). They were all compared with ‘no screening’ in their respective evaluations. The Health Promotion Administration in Taiwan integrated its screening program into public healthcare via the provision of free biennial oral mucosal examinations for high-risk citizens [The strategies explored mostly consisted of population-based screening  of OPMD to be established over the life span of patients. Van der Meij et al.  estimateOn the contrary, the RCT in India focused on the real-time outcomes from three screening cycles over a shorter period of nine years . They meIt is worth highlighting that three out of the four modeling studies had similar estimates for health utility values ,20,21. TThe ICER of strategies is summarized in The threshold adopted appeared to be dependent on the availability of a national willingness-to-pay threshold and local recommendations for conducting an economic evaluation. Both Huang et al.  and SubrThree studies applied state-transition Markov modeling to the economic evaluation of the screening programs ,21,22, wAll the models adopted a stage-shift approach to the screening effect, with varying methods. In the decision model by Van der Meij et al. , this waThe four modeling studies were further assessed for risk of bias using the simplified Philips checklist . All theBoth Van der Meij et al.  and DedhKumdee et al.  carried It is worth highlighting that while sensitivity analysis was not possible for both the observational study and the RCT, the studies did point out the potential sample uncertainties arising from sampling and data organization. All the modeling studies carried out various sensitive analyses for a range of inputs. Dedhia et al.  found, fBoth Speight et al.  and KumdOverall, the total number of studies on screening programs for oral cancer was rather small compared to other types of cancer, such as prostate and breast cancer ,25. FurtNevertheless, newer studies incorporating modeling approaches, even though limited, are showing potential for application in future research to fill these evidence gaps . They arGenerally, all studies reported that several implementations of screening initiatives were cost-effective compared to not screening for oral cancer. It was, however, difficult to provide recommendations on the best screening options as the evidence differed based on country, setting, payer system, costing approach, and parameters modeled. Nevertheless, a valid comparison between screening measures can still be extracted from the various scenarios modeled by Speight et al.  and KumdIn the setting of a developed country (the United Kingdom), population-based screening was shown to incur higher costs compared to opportunistic screening. This was predominantly contributed by the huge amount of resources required to cover a larger population. Nevertheless, if the coverage was narrowed to either opportunistic screenings or focused on high-risk individuals, the screening strategies showed improvements in terms of their ICER values . In shorThe study in Thailand, on the other hand, gave an alternative paradigm of a developing Asian country. They evidenced that strategies that involved multiple healthcare personnel incurred a higher cost but with minimal improvements in terms of QALY gained. Thus, it was critical for a balance to be achieved between the accuracy of the diagnosis and the number of personnel involved in the screening process. Encouraging oral self-examination facilitated a reduction in dentists’ workload and made the program more feasible on a national scale. Additionally, in situations where there are insufficient dentists in the public healthcare system, a well-trained dental nurse can be considered for the success of these screening programs .At the current moment, the natural history model for oral cancer with its wide array of premalignant lesions and conditions remains to be validated . An inveHealth states should be based on the TNM staging system. This is because it allows the states to be informed about management decisions according to practice and treatment guidelines. All three of the Markov state transition models reviewed here establish that such a design can mirror real-world outcomes and envisage future costs. Models must also incorporate both treated and untreated cohorts to reflect the reality of the current population mix. Despite the predictability of such cure models, which are yet to be established, it avoids the overestimation of comparisons made solely with the untreated group.Due to the scarcity of published studies, the intuitiveness of the Markov models could not be contrasted with other methods such as discrete-event simulation and stochastic models. Based on this review, the cohort-level simulation was less intricate, easily simulated, and needed less computational time for analysis while maintaining its robustness. The key drawback of the Markovian process being ‘memoryless’ was also demonstrated to be easily countered by incorporating tunnel states into the existing model structure ,21. ThisAll four of the modeling studies incorporated QALY to capture the morbidity and mortality of oral cancer progression and treatment effects. While they are a good proxy to corroborate the effectiveness of screening programs, utility values need to be accurate and reflective of the investigated population and time frame. The QOL values based on the findings in England in 1997 in three of the studies, for instance, may not represent the current local healthcare system and patient responses . FurtherIt is also imperative for researchers to adopt modeling approaches to conduct extensive sensitivity analysis and explore strategy-specific challenges. This is because the assumptions and input parameters can alter the direction of the cost-effectiveness of strategies considerably. Parameters such as MTR, screen and treatment compliances, screening performances, treatment effects, and incidences should primarily be explored for all possible ranges in the population. Although the deterministic sensitivity analysis was sufficient to characterize these uncertainties, a probabilistic sensitivity analysis may better establish the structural uncertainties of the model . AdditioThe most significant strength of this review is its extensive, in-depth analysis of study designs for oral cancer screening evaluations. The comparison of designs and conduct allows future investigators to adopt feasible and robust methods for their setting. Additionally, the study reiterates the gaps in the reliability of the evidence for the cost-effectiveness of screening strategies, which prevent their recommendation and institutionalization. Areas such as the inclusion of comprehensive costing components and the incorporation of more recent and local health utility values are critical for steering decisions on the implementation of screenings. With a huge population scope, high programmatic costs, and numerous variations in conduct and values, the review demonstrates the modeling approach as a feasible solution to fill the knowledge gaps before initiating more resource-intensive trials.One of the major limitations of the review is that the disparity of studies does not allow for a direct comparison of cost-effectiveness values and study quality. This was best illustrated in terms of the cost implications, where the broader societal perspective led to larger financial implications compared to those from the perspectives of healthcare providers alone. The lack of patient expenditures and indirect costs underestimates the economic consequences and limits the interpretability of findings in different settings.In our review, a compromise was made to adopt more lenient inclusion criteria to represent and discuss numerous study designs instead of focusing on inter-study outcomes. This aimed to encourage the construction of study methods to tackle the lack of economic evaluation in oral cancer screening. As echoed by the Cochrane Oral Health Group and US Preventative Services Task Force (USPSTF), the cost-effectiveness of visual examinations in oral cancer screening can only be evaluated and established when a wealth of information has been accrued ,32.This review also did not include gray literature or studies in other languages. Furthermore, while numerous oral screening programs are conducted around the world as part of national healthcare services or institution-driven, these programs are often neither reported nor evaluated economically. This could significantly skew the review’s narrative and focus. Appraising, reporting, and compiling these initiatives can help build up the sufficient evidence needed to build local models and assist in decision-making at a national level.The current evidence of the cost-effectiveness of oral cancer screening is still heterogeneous and inadequate to support its institutionalization. However, the available data points toward certain implementational strategies being possibly cost-effective. While trials and observational studies were able to provide accurate information on the cost of programs, modeling approaches appeared favorable as they could generate a wealth of information for decision-making. The state-transition model with built-in tunnel states was able to reflect the impact of screening strategies adequately. As the models and decisions were shown to be very sensitive to assumptions and input parameters, the review reinforced the need for more critical sensitivity analysis and validation steps. We hope that our findings can encourage a more robust exploration of economic evaluations in oral cancer screening to fill the current knowledge gaps.


In the mammalian brain, neurogenesis is maintained throughout adulthood primarily in two typical niches, the subgranular zone (SGZ) of the dentate gyrus and the subventricular zone (SVZ) of the lateral ventricles and in other nonclassic neurogenic areas . During prenatal and early postnatal development, neural stem cells (NSCs) differentiate into neurons and migrate to appropriate areas such as the olfactory bulb where they integrate into existing neural networks; these phenomena constitute the multistep process of neurogenesis. Alterations in any of these processes impair neurogenesis and may even lead to brain dysfunction, including cognitive impairment and neurodegeneration. Here, we first summarize the main properties of mammalian neurogenic niches to describe the cellular and molecular mechanisms of neurogenesis. Accumulating evidence indicates that neurogenesis plays an integral role in neuronal plasticity in the brain and cognition in the postnatal period. Given that neurogenesis can be highly modulated by a number of extrinsic and intrinsic factors, we discuss the impact of extrinsic  and intrinsic  modulators on neurogenesis. Additionally, we provide an overview of the contribution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection to persistent neurological sequelae such as neurodegeneration, neurogenic defects and accelerated neuronal cell death. Together, our review provides a link between extrinsic/intrinsic factors and neurogenesis and explains the possible mechanisms of abnormal neurogenesis underlying neurological disorders. The central nervous system (CNS) is the most important component of the human nervous system and receives and integrates afferent inputs from all over the body, playing a crucial role in brain functions such as learning, memory and emotion . The CNSIt has been reported that symptoms such as depression, anxiety, cognitive, or olfactory dysfunction are observed in the early stages of neurodegenerative disorders such as Parkinson’s disease (PD), Alzheimer’s disease (AD) and Huntington’s disease (HD) prior to disease-specific patterns of neurite degeneration and neuronal loss ,12,13. TThis review provides a detailed discussion of the effects of extrinsic and intrinsic factors on neurogenesis, as well as the molecular mechanism underlying neurogenesis, which may provide better insight into the mechanisms of neurodegenerative disorders and new directions for their treatment.In 1992, Reynolds et al. described a cell population isolated from the striatum of the adult mouse brain that could divide and proliferate continuously in vitro and had the potential to differentiate into a variety of cell types; this discovery of NSCs challenged the traditional theory that adult mammalian nerve cells cannot regenerate . SubsequNeural stem cells are undifferentiated primitive cells that do not express mature cellular antigens, have low immunogenicity and are not recognized by the immune system. In addition, NSCs can coexist well with host neural tissue and survive in the host for a long time . TherefoNeurogenesis is a critical process throughout life and involves the generation of new functional neurons from NSC NPC and neuroblast proliferation, the differentiation, maturation and maintenance of neurons and the migration and integration of new neurons into existing brain circuits . These sNeural stem cells undergo proliferation and self-renewal by symmetric and asymmetric cell division to maintain the NSC pool . SymmetrNeural stem cells also have the capacity to differentiate into neurons, oligodendrocytes and astrocytes, which are closely linked to factors in the local microenvironment such as growth factors. During brain development, NSCs differentiate in a temporal manner, with neurogenesis occurring first, followed by gliogenesis. In rodents, neurogenesis begins in the early embryonic stages (E10~E11) and continues until birth, although dendritic and axonal maturation continue postnatally. Gliogenesis begins in the late embryonic stages and peaks at birth ,36. In hIn addition, resident NSCs in the SVZ undergo asymmetric neurogenic cell division to generate daughter cells that differentiate into restricted neuroblasts prior to migration to the OB via the rostral migratory stream (RMS) . FurtherJust before birth, RGCs produce NSCs, which serve as a pool for adult neurogenesis and developmental processes ,48. In tThe SVZ is situated along the ependymal cell layer of the lateral walls of the lateral ventricles and contains a subpopulation of resident NSCs in the resting state  that have radial-glial-like characteristics and form the vasculature, ending with blood vessels in the SVZ . In the In addition, type B cells maintain direct contact with the cerebrospinal fluid (CSF) in the lateral ventricles by extending their apical end into the ependymal layer B. The adThe hippocampus is the primary brain region responsible for memory consolidation, in which the highly orchestrated neuronal network between the entorhinal cortex, DG and cornu ammonis is essential . The othLocal NSCs in the SGZ, also called type 1 cells, have the molecular characteristics of astrocytes and the morphology of radial glia-like (RGL) cells, resembling embryonic neural progenitors, and have self-renewal and multipotential capacities ,62. TypeDuring the process of neurogenesis, a subset of newborn cells is generated in the SGZ each day, while most cells die by a two-step process. A large portion of cell death occurs during the early developmental period (24~48 h postmitosis) via apoptosis. Surviving cells in this stage migrate to the GCL and continue to mature . Cell deThe hypothalamus is known for its role in regulating autonomic function and body homeostasis and has recently been identified as a third neurogenic niche. Pioneering studies demonstrating the neurogenic capacity of the hypothalamus were first conducted to aid the growth and expansion of differentiated postnatal neurons, which were originally thought to be challenging due to the terminally differentiated state of the neurons . NeuronsThe striatum plays a key regulatory role in the dopamine pathway, and the dysfunction of this system can lead to cognitive and psychiatric diseases such as schizophrenia and Parkinson’s disease.Retrospective cell birth dating techniques have enabled scientists to examine DNA synthesis and the generation of new cells and determine the age of cells by assessing temporal changes in the levels of isotope carbon-14 in genomic DNA . This haThe human amygdala comprises 13 nuclei in the rostral temporal lobe that function to assign emotional salience to a vast spectrum of external stimuli and encode memories largely through fear learning and anxiety. Amygdala dysfunction has been implicated in the pathophysiology of human mood and anxiety disorders ,101. ForDifferent pathological and physiological stimuli can impact the entire neurogenesis process . Adult hDifferent pathological and physiological stimuli can impact the entire neurogenesis process . There iAnother important extrinsic factor is stress. Stress impairs hippocampal neurogenesis, induces anxiety- and depressive-like behaviors and is known to result in increased drinking ,123. StrRadiation exposure is also an important extrinsic factor that increases the risk for cancers and noncancerous diseases, such as atherosclerosis and neurodegeneration . Brain tTraumatic brain injury (TBI) is a leading cause of injury-related mortality and morbidity worldwide and is characterized by cognitive dysfunction and neuroinflammation. Traumatic brain injury symptoms range from mild to severe depending on the site and severity of the injury and volume of damaged tissue. The risk of neurodegenerative diseases, such as AD and PD, is increased in patients with TBI ,141. It An uninterrupted supply of oxygen (O2) to the brain is necessary to maintain cellular homeostasis and energy metabolism . It has Proper nutrition is important for CNS maturation and functional development. Preclinical studies indicate that high-calorie diet consumption impairs adult neurogenesis, leading to reductions in the proliferation of cells and the differentiation of neuroblasts/neurons and memory deficits in rats and mice ,174,175.In late 2019, a viral outbreak of a novel zoonotic enveloped RNA betacoronavirus of the family Coronaviridae  that is Studies of previously known coronaviruses, such as SARS-CoV-1 and Middle East respiratory syndrome-related coronavirus (MERS-CoV), have shown that viral entry relies on the binding of angiotensin-converting enzyme 2 (ACE2)  and dipeInterestingly, a clinical comparison of microstructural and volumetric changes between recovered COVID-19 patients’ brains and the brains of individuals without COVID-19 revealed that recovered COVID-19 patients show the regional enlargement of brain areas, especially in the central olfactory system , which iThere is a lack of adequate sample size, sex, age and neurologic symptom and stage matching across these studies, and the precise mechanisms of COVID-19-induced neurogenesis and neurological deficits remain largely unknown. Nevertheless, the neuropathological and psychiatric complications of COVID-19 (including in patients who have recovered and asymptomatic patients) need to be further elucidated as they represent major public health challenges.While external factors affect neurogenesis, some intrinsic factors also play an important role in the regulation of neurogenesis. The possible mechanisms involved in the regulation of neurogenesis by these intrinsic factors are described in detail below and summarized in Hormones, which play an important role in coordinating physiological processes such as metabolism, growth and development, are chemicals synthesized by highly differentiated endocrine cells and secreted directly into the blood. It has been reported that different kinds of hormones, including sex, stress and metabolic hormones, are involved in regulating embryonic and adult neurogenesis and dendritic morphology . Both feThe most striking difference in brain morphology between males and females is size, with males having, on average, a larger brain than females . Kelava Once the body perceives a stress, danger, or threat in the environment, it responds by releasing stress hormones that stimulate the energy storage system and activate the sympathetic system . ChronicThe majority of colonizing microbes in the human body exist within the gastrointestinal tract . In receGiven the important effects of the gut microbiota early in life ,274, it This information highlights the potential of novel therapeutic strategies targeting the gut–brain axis to either slow cognitive decline or promote neuronal regeneration or neuronal repair mechanisms. Unfortunately, most of these studies were performed in animals of varying ages, and the mechanisms underlying intestinal microbiome-induced neurogenesis and the effects of intestinal microbes on brain functions are unclear due to the complicated orchestration of a wide variety of gut microbes and immune cells. In addition, it is difficult to know if the findings are translatable to human subjects. Further studies are required to better delineate the regulatory mechanism of bidirectional gut–brain communication in adult neurogenesis and cognitive function.Aging is an unavoidable nonpathological process that can link health and disease, and it is one of the most important risk factors for compromised brain function and plasticity, including the disruption of adult hippocampal neurogenesis-mediated structural/functional plasticity and mood modulation. Although neurogenesis occurs throughout life, a marked reduction in adult hippocampal neurogenesis along with aging was observed in the hippocampal DG of rodents, carnivores, nonhuman primates and humans, showing that the number of RGLs and intermediate progenitors, the proliferation and differentiation of NSCs/NPCs and the survival rate of adult newborn neurons are decreased ,284,285.In addition to intrinsic cellular alterations, changes in the systemic environment during aging are important factors influencing adult neurogenesis. Using a model of heterochronic parabiosis, it has been demonstrated that immune-linked molecular and cellular changes in the systemic environment that occur with aging inhibit adult neurogenesis ,292. In Neurogenesis, especially adult hippocampal neurogenesis, which plays an important role in several hippocampus-dependent functions, is now a key topic in neuroscience. A large number of studies have elucidated the process by which cells are initially formed and identified when and where these cells undergo cell division and then differentiate. The process of differentiation is complex and long, and it includes various steps, such as migration, morphological and molecular differentiation and the final integration of new neurons into preexisting neural networks . As eluc


In clinical scenarios, the use of biomedical sensors, devices and multi-parameter assessments is fundamental to provide a comprehensive portrait of patients’ state, in order to adapt and personalize rehabilitation interventions and support clinical decision-making. However, there is a huge gap between the potential of the multidomain techniques available and the limited practical use that is made in the clinical scenario. This paper reviews the current state-of-the-art and provides insights into future directions of multi-domain instrumental approaches in the clinical assessment of patients involved in neuromotor rehabilitation. We also summarize the main achievements and challenges of using multi-domain approaches in the assessment of rehabilitation for various neurological disorders affecting motor functions. Our results showed that multi-domain approaches combine information and measurements from different tools and biological signals, such as kinematics, electromyography (EMG), electroencephalography (EEG), near-infrared spectroscopy (NIRS), and clinical scales, to provide a comprehensive and objective evaluation of patients’ state and recovery. This multi-domain approach permits the progress of research in clinical and rehabilitative practice and the understanding of the pathophysiological changes occurring during and after rehabilitation. We discuss the potential benefits and limitations of multi-domain approaches for clinical decision-making, personalized therapy, and prognosis. We conclude by highlighting the need for more standardized methods, validation studies, and the integration of multi-domain approaches in clinical practice and research. In clinical scenarios, clinical scales are the most-used tools for the evaluation of patients’ neuromotor impairment and the assessment of recovery after rehabilitation. Despite their widespread use, clinical scales present some limitations that affect the reliability, objectivity, and sensitivity as well as the feasibility of use, related to cost-effectiveness and ease of administration . BesidesTherefore, in recent decades, clinicians have started to rely on the availability of tools, devices, and techniques for the analysis of biological signals, exploiting their added value in comparison to the standard clinical practice; the innovative, highly advanced, and pioneering approaches favor the adoption of multi-modal solutions and the improvement of the assessment of rehabilitation effectiveness in a plethora of pathologies. This process boosts the progress of research in clinical and rehabilitative practice and improves the understanding of the pathophysiological changes occurring during and after rehabilitation, overcoming the low sensitivity of traditional clinical practice. Instrumental measurements, such as kinematic recordings, electromyography (EMG), electroencephalography (EEG), or near-infrared spectroscopy (NIRS), are widely used in clinical scenarios and can provide quantitative assessments of the patient’s health state. Each instrumental assessment explores and provides information about a specific domain: kinematic recordings allow us to quantify motor performance and quality of movement by directly assessing the motor outputs; EMG measures the activity of muscles and can be useful for muscle-fatigue detection, force estimation, and motor-control analysis; EEG measures the electrical activity of the brain and can monitor the complex neuronal activity and its changes; NIRS measures the hemoglobin concentration in human tissue and can assess the hemodynamics in the brain cortex or muscles. However, since motor and neural functioning are complex structures involving individual, environmental, and contextual factors, a multi-modal comprehensive characterization of the patient is needed to overcome the limited view that is provided when using only one sensor at a time. It is unlikely that a single outcome measure may adequately assess the degree of neuromotor functions and differentiate between key elements of the same function. Indeed, multi-domain approaches combine information and measurements that are collected with sensors from different domains, such as kinematics, EMG, EEG, NIRS, and others. Each domain gives specific information that, combined with the other measurements, may provide a more comprehensive understanding of the state of the patient. This may explain why, in research studies, different clinical outcome measures have been integrated to capture different domains of the same function and different domains of the International Classification of Functioning, Disability, and Health (ICF)  to gain a more complete picture of functioning. In fact, in many neurological disorders, the impairment regards the neural and sensorimotor systems at different levels, and, therefore, a detailed quantitative assessment is essential for the definition of rehabilitation treatment and the evaluation of the recovery . TherefoMulti-modal approaches allow us to choose the most effective treatments and, prospectively, provide the best care methods for patients. These methodologies may be integrated into clinical practice to support clinical decisions, to provide a comprehensive assessment of the patient and quantitatively evaluate motor recovery during rehabilitation. However, the main findings achieved using multi-parameter assessments and the potentiality of combining measures from multiple domains have not been summarized to guide future directions in the clinical field.This paper provides a detailed overview of the current scientific research based on multi-modal and multi-parameter assessments in the clinical field and suggests how to improve scientific and clinical research to promote the use of multi-domain approaches, in order to foster the application of multi-parameter assessment in clinical practice by showing clear evidence of its potential. This overview focused mainly on musculoskeletal and central nervous system (CNS) assessment in rehabilitation.This narrative review aims at collecting and reviewing the main multi-domain instrumental approaches that are currently employed in clinical assessments, with a particular focus on the rehabilitation field. We would like to (i) provide a summary of the main domains assessed with instrumental technologies, (ii) summarize which combinations of multi-domain instrumental approaches have been used so far, (iii) describe the main achievements obtained, and (iv) critically comment on the future directions for the field.The findings that will be summarized come from a vast field and from variable approaches. A screening of the literature was performed, and the most representative articles were selected based on the authors’ experience. Only papers available in the main databases  and written in English were considered for selection. From this analysis, the main advantages and disadvantages of the multi-domain approaches will be discussed, highlighting how future research and clinical practice would be impacted by these techniques.A scheme of the main instrumental approaches related to different physiological domains investigated in this work is shown in People with neurological conditions can suffer from several impairments, ranging from paresis associated with decreased strength and sensation to increased muscle tone, loss of inter-joint coordination, and impaired control of voluntary movement that results in slow, imprecise, and uncoordinated task-related movement . These iSeveral systematic reviews, guidelines, and consensus-based recommendations have evaluated the psychometric properties and/or feasibility of clinical outcome measures  in neuroWithin the ICF Body Structure/Body Function level, a variety of assessment scales exist to evaluate motor impairment after stroke, designed to capture aspects such as joint range of motion (ROM), strength, synergistic execution of movements, gross motor capabilities, and object manipulation. These assessments concern movement strategies used to accomplish a task and try to identify the factors that may affect the performance of a task. In the last few decades, the focus of rehabilitation has slowly shifted from ICF function level towards activity and participation level . The limIn the last few years, several recommendations combining existing evidence, clinical practice guidelines, and expert consensus have provided a core set of outcome measures for upper- and lower-limb assessment in neurological rehabilitation . Most ofAnother drawback of the clinical outcome measures is that they are insufficiently sensitive to capture the quality of sensorimotor performance. This impedes the ability to clearly distinguish behavioral restitution or compensation, which is essential for understanding the neurological mechanism of sensorimotor recovery post-stroke . A better understanding of the relationship between movement quality and the ability to perform functional activities can be achieved with a detailed analysis of the joints/body segments involved in accomplishing a particular task . This isClinical outcome measures have also been used as predictors of recovery potential . A rangeKinematic evaluations can provide quantitative and objective information about motor output associated with tasks and allow for monitoring the administration of therapeutic techniques . KinematThese parameters can be measured with optoelectronic systems that require a set of infrared cameras and retroreflective markers placed on anatomical landmarks of the patients, or marker-less systems, such as RGB-depth cameras or IMUs. Parameters related to movement speed are usually movement time, mean velocity , and peaKinematic measures provide insight into the movement execution and functional outcomes of the neurological system performance of the patient; however, they cannot identify coordination patterns and the underlying mechanisms of impairments, which can be detected with other neurophysiological measures .Surface EMG is a non-invasive technique used to record the activity of the muscles under the electrodes placed on the skin . The acqCommon applications in the time domain are the estimation of the number of motor units (MUs), the detection of muscle activity, and the analysis of muscle co-contraction. The number of MUs has been identified as a biomarker for the progression of neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS) . The detDespite its numerous applications, the EMG signal is affected by the structure and the placement of the electrodes  and by tIn clinical scenarios, EMG analysis has been used for a variety of assessments. Current applications of EMG are mainly related to physiological investigation, the monitoring of neurological disorders, and the planning of treatments . The evaEEG is a technique that measures the electrical activity of the brain from electrodes attached to the scalp. EEG has a high temporal resolution, meaning that it can capture fast changes in brain activity with millisecond accuracy . EEG sigWith the advent of high-density systems, it is possible to monitor whole-brain neuronal activity with a better spatial resolution, which is more suitable for exploring functional network organization . Indeed,Moreover, graph analysis has been successfully employed to concisely describe the brain network’s integration and segregation behavior in communication . The braEEG is thus a valuable tool for studying how the brain changes and recovers its functions after injury or disease, such as stroke, Parkinson’s disease (PD), cerebral palsy (CP), spinal cord injury (SCI), or traumatic brain injury (TBI). EEG has several advantages over other neuroimaging techniques, such as being affordable, portable, easy to use, and adaptable to different situations. EEG can work both in rest and movement conditions, and it can be combined with other modalities, such as EMG, kinematics, functional NIRS (fNIRS), or transcranial magnetic stimulation (TMS). EEG can reveal various aspects of brain function that are relevant for motor rehabilitation, such as event-related potentials (ERPs), power spectra, and connectivity measures. ERPs are time-locked changes in EEG signals that reflect the brain’s response to specific stimuli or events. Power spectra show the distribution of EEG signal energy across different frequency bands. Connectivity measures show how different brain regions interact with each other. EEG is a widely used technique to study the brain changes that occur during and after post-stroke rehabilitation, across different stages of recovery . EEG bioIn addition to traditional biomarkers, more recently, FC investigation proved to be particularly interesting in the study of rehabilitation effects in those pathologies derived from the disruption of information transfer between brain regions and helped to explore how induced brain plasticity may play an important role in functionality recovery .In the following text, we focus on summarizing more recent findings of FC analysis, undirected or directed, in the field of motor rehabilitation treatments.Brain connectivity in the resting state (RS) is one of the most investigated conditions since it is the easiest experimental protocol that can be performed with patients of all grades of impairments, and it has been demonstrated that RS connectivity is predictive of motor-function recovery in stroke patients . NeverthMost of the studies evaluating the effect of rehabilitation in motor recovery focused their analysis on motor-network characterization. However, altered motor-network FC has also been found with higher-order cognitive control networks such as default mode networks, executive control networks, and dorsal attention networks. Therefore, connectivity patterns have been recently investigated both within and between RS large-scale networks ,74,75.In the literature, the major results of connectivity analysis in the rehabilitation field are focused on stroke recovery, comparing stroke patients with control groups ,76,77,78Philips et al. in 2017 proved that topographical measures of integration and segregation among functional networks may be useful biomarkers of post-stroke motor recovery, suggesting their employment for the prognosis and evaluation of therapeutic outcomes . Many stAs for large-scale intra-network connectivity, Romeo et al. investigated the interaction of 14 RS networks and their correlation to different impairment domains in a cohort of 30 sub-acute/chronic stroke patients. Interestingly they found a correlation between dorsal attention networks and language network FC with motor indexes . Wang etNIRS is a non-invasive optical technique that allows for the measurements of hemoglobin concentration in human tissues using light in the near-infrared region (650–900 nm). Light is shone into the biological tissue and recollected from the same by means of optical fibers. The injected photons travel in the whole volume under the optical fibers and the features of the recollected signal depend on the different tissue optical properties, i.e., the absorption and diffuse coefficients .2Hb) and deoxygenated-(HHb) hemoglobin concentrations, allowing for the calculation of tissue total hemoglobin (tHb) content and tissue oxygen saturation (SO2 = O2Hb/tHb). The main physiological parameters investigated with this technique are the oxygenated-(O2Hb and a concomitant decrease in HHb in the brain cortex) after the administration of stimuli of different natures. In this case, the optical probe is placed on the scalp and photons travel through the head, reaching the brain cortex after going through the skin, the skull, and the cerebrospinal fluid. This kind of study is referred to as functional NIRS (fNIRS) [2 extraction, typically represented by a concomitant increase in HHb and a decrease in O2Hb [Among the applications of NIRS, we mention the measure of the cortical response function  . Another in O2Hb . In thisBecause of the hardware simplicity and moderate price, the most common approach for NIRS acquisitions is based on the employment of continuous wave (CW) optical radiation. CW NIRS allows us to retrieve relative variations of the hemodynamic parameters with respect to an arbitral baseline . In thisFinally, NIRS is a relatively low-cost, noninvasive technique that can be made multichannel and can be easily applied at the bedside for the continuous monitoring of the hemodynamic parameters. Moreover, it is compatible with various other clinical techniques. For these reasons, it has already been employed in different scenarios and different clinical settings, even if it can be still considered quite a new technology. In the following, some examples are presented, giving wider importance to the rehabilitation scenario and focusing on both the brain and muscle applications. In Lastly, another optical technique was recently introduced in combination with fNIRS: diffuse correlation spectroscopy (DCS), which allows for the investigation of the motion of red blood cells and calculating cerebral blood flow, exploiting the coherence loss of highly coherent laser light when it diffuses in biological tissues . For furOne of the main applications of fNIRS is the measure of brain cortex hemodynamics in response to neural activity, which allows researchers to investigate a wide range of cognitive and motor processes connected to rehabilitation. It has also been widely leveraged in clinics to assess cerebral hemodynamics in patients suffering from stroke , TBI 9595, or deIn the neuro-rehabilitation contest, compared to other neuro-imaging techniques such as fMRI, whose studies in this framework are limited to the upper-extremity exercises, fNIRS allows us also to investigate brain oxygenation during the exercise of the lower limbs, being less prone to motion artifacts. An important type of study where fNIRS is exploited concerns the monitoring of the rehabilitation process, to investigate the mechanisms of functional recovery after brain injury. In other cases, fNIRS was used as a therapeutic tool to develop brain–computer interface modules (BCI) . Many pa2, blood pressure, skin conductance, skin temperature, heart rate, respiratory rate, photoplethysmography, and others), which can be also used for regressing out physiological confounding components in fNIRS signals [Due to fNIRS acquisitions on the cerebral cortex, we have information about neurovascular coupling. This process is always more considered, together with other parameters acquired in the clinical practice, in order to have a comprehensive view of the cerebral cortex’s functioning and state. With fNIRS, it is easier to perform experiments when the subjects are walking or performing rehabilitation exercises, thanks to the possibility of making this technique portable ,102. Rec signals . In the 2 saturation and oxygen consumption (2) as a measure of muscular oxidative metabolism [The employment of NIRS techniques on muscular tissue allows for the determination of local musculoskeletal Otabolism . In a retabolism . In parttabolism , and thetabolism . Skeletatabolism . Manfredtabolism . The efftabolism . Finallytabolism .In this section, we reported multi-domain approaches that were found to be most diffused in clinical applications. We discuss in detail the combinations of instrumental approaches from different domains.EEG and EMG signals regard functional activities that are strictly correlated: the EEG measures the activity at the brain motor cortex, where the motor commands start, while the EMG quantifies the muscle activations that are generated by those commands. Therefore, EEG + EMG analysis may give insights into how each of the two domains is affected by the impairment and restored with the rehabilitation, supporting the therapy decision process and the evaluation of the motor recovery . The mosBiomechanical and neural activity provide complementary information about the neuro-musculoskeletal system of the patient with an objective approach . The comEEG measures can provide complementary information on motor cortex activations and brain connectivity that can be related to the motor output evaluated by kinematic measurements. In post-stroke patients, both domains were positively affected during rehabilitation , indicatThe combination of EMG with NIRS allowed us to assess muscle characteristics from both an electrical and hemodynamic point of view . PrincipThe multi-modal approach EEG-fNIRS provides complementary information to explore neurovascular coupling. In the literature, it is possible to find tens of applications of combined fNIRS-EEG acquisitions, because of the orthogonality of the neurophysiological information provided by the two technologies. Among the clinical applications, rehabilitation is present for only 8% , probablCombining tissue oxygenation (measured by NIRS), blood flow (by DCS), and arterial saturation  it is possible to measure the tissue metabolic rate of oxygen consumption. In the literature, we can find examples of their combined clinical application on the neonatal brain. In 2010, Durduran et al. measured cerebral hemodynamics and oxygen metabolism in neonates with congenital heart defects, and they observed a good agreement with gold-standard arterial spin-labeled magnetic resonance imaging . More reRecently, the DCS technique was also applied to periphery body compartments to obtain information about systemic tissue perfusion and vascular diseases . Many paA multi-domain assessment could also be useful in muscular applications. In particular, there are many examples where both the central and peripheral aerobic functions have to be monitored, such as in chronic heart failure (CHF) patients . To bettInstrumental assessments provide quantitative information on the neuromotor and motor recovery of patients during and after rehabilitation. Such evaluations cannot be reliably performed using standard clinical scales only. Furthermore, the combination of the analysis from different domains provides a comprehensive and complementary evaluation of the patient, which may help to better understand the organization and rearrangement of the central nervous and musculoskeletal systems . The intEach tool, device, or sensor provides specific information related to its specific domain, allowing for a deep—but limited to the domain—characterization of the patient. A more comprehensive characterization of the patient is needed to tailor rehabilitation therapies, since pathologies affect each patient differently , and mulIt is indeed clear from available studies that multi-parameter approaches offer a set of interpretative advantages that may strongly affect the comprehension of the mechanisms underlying pathologies and clinical decision-making. It is, however, also clear that the field of multi-domain approaches is based on pilot studies and has not yet found wide application in clinical studies, since these approaches also show disadvantages.Multi-domain instrumental approaches have some limitations that have prevented their systematic use in clinical practice. First of all, employing multiple sensors would require a long preparation time that is not feasible for routine assessments in clinics, in which the time dedicated to a single patient is limited . MoreoveFurthermore, the use of simultaneous multiple recordings results in a large number of sensors and cables being attached to the patient. This leads to multiple possible consequences. First, from a technical point of view, sensors may interfere and cause relative movements or the detachment of the sensors themselves from the skin. Indeed, recordings can be contaminated by electronic equipment, such as power line noise and cable motion artifacts, and by movement artifacts at the electrode–skin interface . Second,Another difficulty for clinical use is the effort required from the clinical personnel: clinicians need practice and training to use different equipment and for interpreting the results, or specific professional figures have to be employed ,167. ThiMost of the scientific articles presenting multi-domain approaches preliminary present studies in which physiological and pathological processes are investigated only in a limited number of patients or even in healthy controls. This set of pilot studies is needed to explore biomarkers that could potentially support diagnosis and decisions on therapy. However, at the present stage, few studies have employed multi-domain measures to evaluate the effects of rehabilitation on motor recovery during training sessions or in pre-post comparisons and longitudinal studies.Even if the potential of multi-domain assessments has only been partially exploited, different approaches could be used for the integration of the parameters from multiple domains. The analytical approach is to analyze the domains separately to characterize each level of the neuro-muscle-skeletal system and, successively, compare the results to find if they are in accordance. In this way, each domain is fully characterized and all the information of each assessment can be captured, as in Belfatto et al. ; howeverThere is a growing body of evidence that rehabilitation-focused biomarkers may provide more accurate information on patients’ stratification and help us to identify the proper respondent during different therapies. In this context, rehabilomics is a new emerging transdisciplinary science based on the evaluation of biomarkers, aiming to understand the rehabilitation-relevant phenotypes related to the biology, function, prognosis, treatment, and recovery of patients with neurological disabilities .The concept behind this approach is that a given biological or molecular system can be better studied by considering it in its entirety, rather than in its individual elements. This principle is also at the basis of systems biology, according to which the study of an organism is considered an integrated and dynamic network of genes and proteins that interact with each other in space and time, allowing a specific system to function.In this context, proteomics, genomics, and metabolomics, alongside functional brain imaging and neurophysiological technologies , have been explored as potential biomarkers of motor recovery in technology-assisted rehabilitation.In clinical rehabilitation practice, the use of a rehabilomic approach along with multi-sensors assessment can be used, for example, to distinguish subjects who have a high risk of developing complications following the proposed rehabilitation treatment from subjects who will not manifest them precisely because of their genetic characteristics and their biomolecular profile. The use of novel biomarkers in the rehabilitation field is useful at several levels: in the preclinical phase, allowing us to identify from the genetic profile the subjects at risk of developing diseases of rehabilitative interest; when the disease has manifested itself, to tailor a treatment to the individual patient, improving the effectiveness and efficiency of the rehabilitation proposal; and finally, it is useful to monitor the effects of the proposal on the individual patient.To spread the use of multi-domain approaches for future applications, limitations of their use in clinical practice should be overcome. Summarizing the findings of our review, we identified specific future directions and barriers to large-scale adoption.(i)Adopt standardized methods and criteria for selecting, combining, and analyzing multi-domain data to ensure the validity, reliability, and comparability of results across studies and settings . To achi(ii)Validate multi-domain approaches against gold-standard measures and clinical outcomes to establish their accuracy, sensitivity, and specificity for different patient populations and conditions;(iii)Integrate multi-domain approaches into clinical practice and research by developing user-friendly interfaces, protocols, and guidelines that facilitate their application and interpretation by clinicians and researchers. The comfort and psychological state of the patient has to be preserved, since the use of many sensors may interfere with the execution of tasks; thus, the sensors should be made less invasive. To foster the use of multi-domain approaches, instrumental measures and clinical observation must be linked so that clinicians may be more encouraged to apply multi-domain approaches and employ such techniques for evaluations and clinical decision-making. Clinicians or other professional figures have to be instructed on the use of the instrumentation and trained to interpret the results ;(iv)Explore novel multi-domain combinations and methods that can capture more aspects of motor function and recovery, such as neural plasticity, muscle metabolism, or cognitive–motor interactions.We expect that future research and practice should:To further clarify the main needs and open points, associated lessons learnt and solutions, we summarized the main points of discussion on the use of multi-domain approaches and the corresponding possible solutions in This work has some limitations. First, the scope of the review is comprehensive and could not systematically cover all the papers available in the literature. While the authors are confident that the vast majority of relevant papers have been screened and reviewed, it is possible that a few studies have been missed. Due to the choice of a narrative approach, in this work no meta-analyses were presented and, thus, only the main messages were presented without detailed assessments. Considering that the field is still lacking clear evidence due to the frontier approach adopted by the inherent studies, our review could highlight many relevant points, but it is not yet able to set precise guidelines for clinical practice.Multi-domain instrumental approaches showed great potential for improving clinical assessment and the rehabilitation of motor function by providing more comprehensive, objective, and personalized information on patients’ states and recovery. Despite some barriers to their systematic adoption in a clinical environment, they represent a fundamental step for research on neurophysiology and rehabilitation and a valuable option for standard clinical practice. Future research will contribute to the fostering of these approaches.


A general consensus acknowledges that drug consumption  constitutes the leading cause of preventable death worldwide. But the global burden of drug abuse extends the mortality statistics. Indeed, the comorbid long-term debilitating effects of the disease also significantly deteriorate the quality of life of individuals suffering from addiction disorders. Despite the large body of evidence delineating the cellular and molecular adaptations induced by chronic drug consumption, the brain mechanisms responsible for drug craving and relapse remain insufficiently understood, and even the most recent developments in the field have not brought significant improvement in the management of drug dependence. Though, recent preclinical evidence suggests that disrupting the hypocretin (orexin) system may serve as an anticraving medication therapy. Here, we discuss how the hypocretins, which orchestrate normal wakefulness, metabolic health and the execution of goal-oriented behaviors, may be compromised and contribute to elicit compulsive drug seeking. We propose an overview on the most recent studies demonstrating an important role for the hypocretin neuropeptide system in the regulation of drug reward and the prevention of drug relapse, and we question the relevance of disrupting the hypocretin system to alleviate symptoms of drug addiction. The cold-turkey alcoholic shaking with delirium tremens might not agree, but only after the body detoxifies does the real challenge begin: staying clean. Ex-addicts with the strongest resolve—and plenty of external motivation in the form of frayed relationships, probationary jobs, or incipient lung cancer—struggle to resist cravings and are susceptible to relapse even years after their last dose Helmuth, .”Quitting a drug habit is not easy to accomplish and the journey to a drug-free life is nothing but an endless personal combat to resist temptations, even long after detoxification. The inability to control drug taking is thought to be a complex disease of the brain that strikes the most vulnerable individuals and worsens with recurring drug intoxication. The use of psychoactive substances causes significant health and social problems for the people who use them, and also for their relatives. The World Health Organization (WHO) recently estimated that over one billion people were tobacco users and that alcohol disorders affected about 80 million people WHO, . In an iIn this context, there is a general consensus acknowledging that the reinforcing properties of drugs of abuse arise, at least in part, from a potentiation of dopaminergic neurotransmission within the mesocorticolimbic circuit. However, in the search for effective treatments alleviating signs of drug addiction, this system still is the subject of pre-clinical drug development studies but the results have been rather inconclusive or are still pending. Meanwhile, emerging data suggests that neurotransmitters other than dopamine may also play important roles in the motivational properties of drugs Boutrel, . The aimThe hypocretins  are two neuropeptides, hypocretin-1/orexin-A, and hypocretin-2/orexin-B, derived from the same precursor gene produced in a few thousand neurons localized in the perifornical area (PFA) of the lateral hypothalamus (LH)  obtained by rats before termination of the session remained unchanged after infusion of the peptide or the receptor antagonist  receptors in the ventral tegmental area (VTA) , which means Hcrt may be critically implicated in addiction disease, most likely in stress- and stimulus-induced drug relapses  in the late nineties and remains to date the most studied Hcrtr-1 antagonist. Several other Hcrtr-1 and Hcrtr-2 antagonists, consensually called SORA for Single Orexin Receptor Antagonists, as well as ligands with similar affinity for both receptors, also called DORA for Dual Orexin Receptor Antagonists, have been developed then. Exhaustive reviews covering patent literature published between 1999 and 2009 have been recently issued  consumption in dependent patients. Unfortunately, it appears quite clear that disrupting the Hcrt system most likely will not reduce cocaine or amphetamine intake. A large consensus remains though on the possibility to treat dependent patients with Hcrt receptor blockers for alleviating symptoms of drug dependence, notably the urge for drug seeking during protracted abstinence from most major drugs of abuse. As reviewed above, the beneficial effects of such a medication may be limited by some serious side effects among which sleepiness, decreased appetite, attention deficits, and reduced libido. In conclusion, there is considerable evidence that the Hcrt system is key to many aspects of reward seeking behaviors and, thus, could be a useful target for controlling relapse for drugs of abuse. However, the fundamental role of these systems in more basic aspects of homeostasis and non-drug reinforcement need to be carefully considered in order to ensure that unintentional adverse consequences are not presented.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.


After birth, the body shifts from glucose as primary energy substrate to milk-derived fats, with sugars from lactose taking a secondary place. At weaning, glucose recovers its primogeniture and dietary fat role decreases. In spite of human temporary adaptation to a high-fat (and sugars and protein) diet during lactation, the ability to thrive on this type of diet is lost irreversibly after weaning. We could not revert too the lactating period metabolic setting because of different proportions of brain/muscle metabolism in the total energy budget, lower thermogenesis needs and capabilities, and absence of significant growth in adults. A key reason for change was the limited availability of foods with high energy content at weaning and during the whole adult life of our ancestors, which physiological adaptations remain practically unchanged in our present-day bodies. Humans have evolved to survive with relatively poor diets interspersed by bouts of scarcity and abundance. Today diets in many societies are largely made up from choice foods, responding to our deeply ingrained desire for fats, protein, sugars, salt etc. Consequently our diets are not well adjusted to our physiological needs/adaptations but mainly to our tastes (another adaptation to periodic scarcity), and thus are rich in energy roughly comparable to milk. However, most adult humans cannot process the food ingested in excess because our cortical-derived craving overrides the mechanisms controlling appetite. This is produced not because we lack the biochemical mechanisms to use this energy, but because we are unprepared for excess, and wholly adapted to survive scarcity. The thrifty mechanisms compound the effects of excess nutrients and damage the control of energy metabolism, developing a pathologic state. As a consequence, an overflow of energy is generated and the disease of plenty develops. Along our evolutionary development we have not needed -so far- to develop control mechanisms for lipid handling, since they are scarce in the environment , and thuThe main role of lipids, from infancy and throughout all our adult life, is limited to constitute the mainstay of our own energy reserves. Consequently, massive mobilization of body fat reserves in adulthood is a strong indication (in metabolic terms) that our energy homeostasis is in jeopardy, and thus we ought to adopt a survival mode ,3. HowevIt is both curious and telling how the pattern of nutrient intake of a high excess of energy in adulthood has a more than casual resemblance with lactation in our early infancy. The coincidence is perhaps even greater because of the choice of foods in present-day adult diets, in which dairy products play a significant role.We are born fully prepared for milk, a lipid-and-disaccharide-based hyperproteic diet. Milk mimics the diet that cause the metabolic syndrome in adulthood: the main carbohydrate is a dissaccharide, the main source of energy is lipid, also rich in saturated fat and cholesterol, and the protein is largely high-quality, with a remarkable proportion of essential amino acids; milk also contains a sizeable proportion of minerals , and water. This complete diet is intended to help us grow fast for a limited time  at the ebaby fat) after being synthesized from maternally-provided glucose [The use of fats as main food is a shift from intrauterine life, in which they are practically not used for energy (its ability to cross the placenta is limited), but stored , we can observe widely different effects. The animals eventually develop obesity ,19, but However, the reversion to lactation of an adult poses serious additional problems. The composition of the diet is not a critical aspect; in fact, the abundance of dairy products themselves combined with the nutrients  present in our diets make them comparable to the nutrient composition of milk. The main problems are those derived from the role of glucose in the regulation of energy distribution between tissues , the matThe prolonged lipid exposure after weaning the rat pups using a cafeteria diet (the same consumed by their dams) results in a rapid and continued growth that soon shifts into obesity and a metabolic syndrome-style derangement ,19. In f1. Loss of the brain ability to adjust energy intake to energy needs (or vice-versa), mainly because the cortical hedonic signals seem to override the basic ponderostat signaling on appetite, compounded by the loss of importance of thermogenesis (depending on body size) as main energy controlling element in the adult ,35 as co2. Conflict between high availability of amino acids and the genetically ingrained drive to preserve amino N, and, especially, essential amino acids, as in starvation ,40; this3. Loss of the primacy of glucose as main inter-organ energy transporter, and alteration of its control because of interfering fatty acids . Muscle 4. Alteration of the function of adipose tissue towards a more passive role of (excess) energy storage rather than its active control of energy availability ; this isX excretion [5. In humans, deep alteration of the microbiota composition, and of our mutualistic relationship with it , via altxcretion ,50, shifxcretion , lower fxcretion ,53. This6. As a consequence of brain and adipose tissue signaling changes (points 1 and 3), regulation of protein turnover  , protectThe metabolic situation in an adult receiving an excess energy diet, with a nutrient composition not too much different from that of milk is different from that of sucklings. Now there is no need of an extra galactose supply for brain galactolipid synthesis, since it is synthesized -on demand- from UDP-glucose . In adulA few of the mechanisms used during our milk-only suckling period are put in action again (at least to a limited extent) in adult overfeeding: increased thermogenesis  and protThe disease of plenty is a wider definition of the metabolic syndrome encompassing a large number of common-origin diseases expressed in parallel to the metabolic syndrome  [1 A more than probable genetic -68 and/o' genes) , complet' genes) ,82.2 Full availability of food, varied food, in which the proportion of high quality protein  is concurrent with sweets  and large proportions of lipid  and salt. The appetite for these historically scarce (and widely desired) materials is ingrained in our brain in an atavistic way , compara3 We endure a marked change in the environmental conditions we are geared for: decreased danger of being pray to predators (if we exclude lawyers and banks), lessened preoccupation for gathering food for the everyday meal, regularity of meals and the possibility of nibbling tasty food almost continuously, choice of foods, abundance of edible materials , but alsThese three factors combine to develop the disease of plenty in a growing proportion of the whole World population. The genetic influence is indubitable because of the evidence gathered in studying population changes ,95 genetThe relationship of the nature and richness (in energy and fats) of the diet as main long-term cause for obesity and related diseases is overwhelmingly accepted. However, the precise reason or mechanism explaining why this excess energy  finds its way into our bloated bodies is the elusive subject of intense research and speculation, as proved by the growing amount of literature published on these issues ,105. NotFinally, sedentary behavior, lack of motivated exercise (there is no need to search for food or to flee from predators) affects a large part of our population . This isIn spite of human temporary adaptation to a high-fat (and sugars and protein) diet for a critical growth and development period -lactation-, after weaning and the end of development into adulthood the ability to thrive on this type of diet is lost. The main reasons for that change are essentially linked to the historically limited availability of high-energy packing foods at weaning and during the whole adult life of humans. Thus our bodies have been adapted for many generations to survive with relatively poor diets interspersed by bouts of scarcity and plentifulness (unpublished). Present-day diets, made up from our deeply ingrained food desire for fats, protein, sugars, salt and hedonic components of food, are markedly rich in energy and these same components listed , similarThe author declares that they have no competing interests.


Either endogenous or exogenous hyperinsulinemia in the setting of insulin resistance promotes phosphorylation and activation of farnesyltransferase, a ubiquitous enzyme that farnesylates Ras protein. Increased availability of farnesylated Ras at the plasma membrane enhances mitogenic responsiveness of cells to various growth factors, thus contributing to progression of cancer and atherosclerosis. This effect is specific to insulin, but is not related to the type of insulin used. Stimulatory effect of hyperinsulinemia on farnesyltransferase in the presence of insulin resistance represents one potential mechanism responsible for mitogenicity and atherogenicity of insulin. Insulin is a major anabolic hormone that governs carbohydrate metabolism and contributes greatly to the metabolism of lipids and proteins. Clinically, its primary role is to promote glucose utilization and regulate hepatic glucose production. At the same time, insulin is an important, albeit mild growth factor. It promotes cell growth, cell division, migration, and inhibits apoptosis. These aspects of insulin action are collectively known as the "mitogenic actions" of insulin  and becaLet us now briefly review the molecular mechanisms by which insulin and hyperinsulinemia, particularly when it occurs in the setting of insulin resistance, can augment proliferative events. In order for all growth factors to stimulate mitogenesis, they must activate the Ras-Raf-Map kinase signalling pathway Figure . Ras proIsoprenylation of Ras is the first step that commits Ras to the process of translocation to the plasma membrane Figure  reviewe]. BecausAs in the case of other growth factors, insulin activates Sos with a subsequent activation of farnesylated Ras and other downstream targets. However, unlike other growth factors, insulin also activates FTase by phosphorylating its alpha subunit ,8. PhospThe crux of the matter is that hyperinsulinemia, whether in cell culture or in vivo , leads to the overstimulation of FTase and excessive farnesylation and membrane association of Ras proteins, whereby increasing cellular responsiveness to other growth factors. This potentiation of the mitogenic effects of other growth factors becomes critical in the pathophysiology of progression of cancer and vascular disease -11.Several in vivo studies provided observational and experimental support to this hypothesis. Thus, liver, aorta, and skeletal muscle of the insulin resistant ob/ob mice and fa/fa rats were found to contain increased amounts of farnesylated Ras . ReductiOverall, we have observed the ability of insulin to potentiate action of IGF-1, EGF, PDGF and VEGF in variety of tissues, including vascular smooth muscle cells, endothelial cells, adipocytes, fibroblasts, liver cells, and breast cancer cells ,4,7,9-15The question that lies before us is - What are the clinical implications of the hypothesis that hyperinsulinemia, in a setting of insulin resistance, exerts significant mitogenic and pro-atherogenic influence? Clearly, acceptance of this postulate would demand an aggressive correction of insulin resistance in order to diminish endogenous compensatory hyperinsulinemia and to minimize exogenous hyperinsulinemia. The most appropriate way of addressing insulin resistance therapeutically is to stress lifestyle modifications - diet and physical activity. Dietary compliance must return to its proper place as a cornerstone of diabetes therapy , while tMost patients with Type 2 diabetes are insulin resistant, and "paying lip service" to dietary and lifestyle therapies leads to overinsulinization. Many patients with Type 1 diabetes who use large doses of insulin to cover for their excessive intake of carbohydrates are also insulin resistant. Carbohydrate counting is an extremely useful tool in diabetes therapy, but consuming dietary carbohydrate without limits also leads to overinsulinization. Use of insulin sensitizers, such as Metformin, would be the second best approach to improving insulin resistance.Several studies have demonstrated the increased likelihood of developing cancer in patients treated with insulin or insulin secretagogues as compared with Metformin ,18. The Undoubtedly, insulin  per se does not cause cancer or atherosclerosis. If anything, insulin, a life-saving hormone, has improved dramatically the life expectancy of patients with diabetes. However, high physiological concentrations of insulin can substantially increase cellular mitogenic responsiveness to other growth factors and promote disadvantageous growth and proliferation, particularly in the presence of insulin resistance.The constellation of the metabolic insulin resistance  and hyperinsulinemia results in overstimulation of the MAP kinase signaling branch and chronic activation of FTase with a subsequent increases in the amounts of farnesylated Ras. These events augment the mitogenicity of other growth factors, thereby promoting the progression of cancer and atherosclerosis .In summary, the detrimental mitogenic effects of hyperinsulinemia must be addressed along with hyperglycaemia when treating diabetes. Endogenous hyperinsulinemia must be treated by minimizing insulin resistance with diet, exercise and insulin sensitizing medications, whereas exogenous hyperinsulinemia must be avoided by selecting appropriate diet and life style while using minimal doses of insulin to achieve normoglycaemia. Inducing hyperinsulinemia as a price for paying "lip service" to dietary therapy is not only inexcusable, but also potentially harmful.The author declares that they have no competing interests.