The neurochemistry of social reward during development: What have we learned from rodent models?

Social rewards are fundamental to survival and overall health. Several studies suggest that adequate social stimuli during early life are critical for developing appropriate socioemotional and cognitive skills, whereas adverse social experiences negatively affect the proper development of brain and behavior, by increasing the susceptibility to develop neuropsychiatric conditions. Therefore, a better understanding of the neural mechanisms underlying social interactions, and their rewarding components in particular, is an important challenge of current neuroscience research. In this context, preclinical research has a crucial role: Animal models allow to investigate the neurobiological aspects of social reward in order to shed light on possible neurochemical alterations causing aberrant social reward processing in neuropsychiatric diseases, and they allow to test the validity and safety of innovative therapeutic strategies. Here, we discuss preclinical research that has investigated the rewarding properties of two forms of social interaction that occur in different phases of the lifespan of mammals, that is, mother-infant interaction and social interactions with peers, by focusing on the main neurotransmitter systems mediating their rewarding components. Together, the research performed so far helped to elucidate the mechanisms of social reward and its psychobiological components throughout development, thus increasing our understanding of the neurobiological substrates sustaining social functioning in health conditions and social dysfunction in major psychiatric disorders.

A rodent cage change insomnia model disrupts memory consolidation.

Insomnia involves disruption of sleep initiation, maintenance and/or overall quality, and may interfere with cognition. Here, we evaluated memory impairment produced by rodent mild (acute) insomnia models. Insomnia models consisted of either single or repeated exposure to cages previously occupied (dirtied) by an unfamiliar rat for 5-7 days. Rats were trained in the Morris water maze to remember the platform location (acquisition), and were then exposed to: (a) 6 hr of undisturbed baseline; (b) dirty cage change-induced insomnia (animal placed into a cage dirtied by another rat for 6 hr); or (c) double-dirty cage change-induced insomnia (animal placed into a cage dirtied by another rat for 3 hr, and then another dirty cage 3 hr later). The animal's memory for the platform location was then evaluated in a probe trial. Double-dirty cage change-induced insomnia significantly disrupted sleep, although the effects of dirty cage change-induced insomnia were overall not significant. In the fourth hour of double-dirty cage change-induced insomnia (following the second cage change), sleep episode number and duration alterations indicated sleep fragmentation. Furthermore, power spectral analysis revealed diminished wake and, to a lesser extent, rapid eye movement theta power (indicated by trend difference) in the last 3 hr of exposure. Significant deficits were noted for measures of water maze performance following double-dirty cage change-induced insomnia, indicating impaired memory. In summary, one variant of the rodent insomnia model, double-dirty cage change-induced insomnia, disrupted sleep and attenuated memory consolidation, indicating this paradigm may be useful to evaluate the effects of hypnotics on memory consolidation.

Mixed infection of Leishmania infantum and Leishmania braziliensis in rodents from endemic urban area of the New World.

BACKGROUND: In Brazil Leishmania braziliensis and L. infantum are the principal species responsible for cutaneous and visceral leishmaniases, respectively. Domestic dogs are the main reservoirs of visceral leishmaniasis, while rodents and marsupials are the main reservoirs for cutaneous leishmaniasis. It has also been suggested that dogs could play a role in transmission of cutaneous leishmaniasis. The identification of the species of Leishmania, the reservoirs, and the vectors involved in each particular transmission cycle is critical for the establishment of control activities. Belo Horizonte has emerged as an endemic region for leishmaniases, however, epidemiological studies assessing the contribution of wild reservoirs to transmission are scarce in the area. The aim of this study was to investigate Leishmania spp. infection in possible reservoirs of an urbanized area. RESULTS: A high rate of infection was found in small mammals (64.9%) and dogs (DG1 30.4% and DG2 48.6%). The presence of L. infantum and L. braziliensis was detected in small mammals and dogs, and mixed infections by both species were detected in rodents which, to the best of our knowledge, is the first description of this phenomenon in an urban area. Additionally, L. amazonensis was detected in the canine samples. CONCLUSION: The possible role of these animals as a source of infection of the vector of each species of Leishmania identified should not be overlooked and should be taken into account in future control activities. The results of mixed infection by L. braziliensis and L. infantum in cosmopolitan rodents as M. musculus and R. rattus, may have important implications in the context of the control of leishmaniasis in urban areas, especially when considering that these rodents live in close relationship with human dwellings, especially those in more precarious conditions.

Effects of stressors in adolescence on learning and memory in rodent models.

This article is part of a Special Issue "Puberty and Adolescence". Learning and memory is affected by a myriad of factors, including exposure to stressors and the corresponding rise in circulating glucocorticoids. Nevertheless, the effects of stressors depend on the sex, species, the type of stressor used, the duration of exposure, as well as the developmental time-point in which stressors are experienced. Effects of stress in adolescence, however, have received less attention than other developmental periods. In adolescence, the hypothalamic-pituitary-adrenal axis and brain regions involved in learning and memory, which also richly express corticosteroid receptors, are continuing to develop, and thus the effects of stress exposures would be expected to differ from those in adulthood. We conclude from a review of the available literature in animal models that hippocampal function is particularly sensitive to adolescent stressors, and the effects tend to be most evident several weeks after the exposure, suggesting stressors alter the developmental trajectory of the hippocampus.

Cecotrophy behavior and use of urea as non-protein nitrogen (NPN) source for capybara (Hydrochoerus hydrochaeris).

Fifteen female adult capybaras, with initial average body weight (BW) of 32.7 (± 5.8) kg, were kept in individual pens to evaluate effect of supplementation of concentrate feed and its supply time on cecotrophy behavior frequency. The animals were allocated in a completely randomized design, with five animals per treatment, receiving three diets: grass only, grass and grain corn offered in a single meal, and grass and grain corn offered in two daily meals; all cecotrophy acts were recorded. Later, in a second experiment, five capybaras received five levels of urea in their diet: 0, 10, 20, 30, and 40 g urea/100 kg BW, replacing soybean meal as true protein source, in a 5 × 5 Latin square design. The animals were weighed and their blood was collected every 2 weeks. The frequency of cecotrophy (Ps < 0.05) was higher when the capybaras were fed grass only (0.5 ± 0.07 acts/h) than when they received grass and corn in a single meal (0.3 ± 0.05 acts/h) and grass and corn supplied in separate meals (0.1 ± 0.03 acts/h). With increased urea in their diet, the capybaras showed initial signs of chronic intoxication, together with increments in serum urea (r = 0.87, P < 0.05) and a decreasing trend in daily weight gain (r = -0.38, P = 0.06). Therefore, when including concentrate feeds in capybara diet, these must be mixed with roughage in a single meal to avoid high decrease in the frequency of cecotrophy behavior and increase in dry matter intake. The replacement of soybean meal with urea in capybara diet is not recommended.

The parental umwelt: Effects of parenthood on sensory processing in rodents.

An animal's umwelt, comprising its perception of the sensory environment, which is inherently subjective, can change across the lifespan in accordance with major life events. In mammals, the onset of motherhood, in particular, is associated with a neural and sensory plasticity that alters a mother's detection and use of sensory information such as infant-related sensory stimuli. Although the literature surrounding mammalian mothers is well established, very few studies have addressed the effects of parenthood on sensory plasticity in mammalian fathers. In this review, we summarize the major findings on the effects of parenthood on behavioural and neural responses to sensory stimuli from pups in rodent mothers, with a focus on the olfactory, auditory, and somatosensory systems, as well as multisensory integration. We also review the available literature on sensory plasticity in rodent fathers. Finally, we discuss the importance of sensory plasticity for effective parental care, hormonal modulation of plasticity, and an exploration of temporal, ecological, and life-history considerations of sensory plasticity associated with parenthood. The changes in processing and/or perception of sensory stimuli associated with the onset of parental care may have both transient and long-lasting effects on parental behaviour and cognition in both mothers and fathers; as such, several promising areas of study, such as on the molecular/genetic, neurochemical, and experiential underpinnings of parenthood-related sensory plasticity, as well as determinants of interspecific variation, remain potential avenues for further exploration.

Sociality, pathogen avoidance, and the neuropeptides oxytocin and arginine vasopressin.

Both humans and nonhumans have evolved a variety of mechanisms to recognize pathogen threat and a variety of adaptive behavioral responses to minimize exposure to it. Because social interactions facilitate the spread of infection among individuals, the ability to recognize and avoid infected and potentially infected individuals is crucial. The neuropeptides oxytocin (OT) and arginine vasopressin (AVP) are involved in mediating various facets of social behavior, including social recognition and responses to salient social threats. Results of studies with rodents have revealed that OT and AVP are also associated with the olfactory-mediated recognition and avoidance of actually or potentially infected individuals. The evidence reviewed here suggests that OT and AVP likely play parallel roles in modulating the recognition and avoidance of socially relevant pathogen threat in both humans and rodents.

Sociality, glucocorticoids and direct fitness in the communally rearing rodent, Octodon degus.

While ecological causes of sociality (or group living) have been identified, proximate mechanisms remain less clear. Recently, close connections between sociality, glucocorticoid hormones (cort) and fitness have been hypothesized. In particular, cort levels would reflect a balance between fitness benefits and costs of group living, and therefore baseline cort levels would vary with sociality in a way opposite to the covariation between sociality and fitness. However, since reproductive effort may become a major determinant of stress responses (i.e., the cort-adaptation hypothesis), cort levels might also be expected to vary with sociality in a way similar to the covariation between sociality and fitness. We tested these expectations during three years in a natural population of the communally rearing degu, Octodon degus. During each year we quantified group membership, measured fecal cortisol metabolites (a proxy of baseline cort levels under natural conditions), and estimated direct fitness. We recorded that direct fitness decreases with group size in these animals. Secondly, neither group size nor the number of females (two proxies of sociality) influenced mean (or coefficient of variation, CV) baseline cortisol levels of adult females. In contrast, cortisol increased with per capita number of offspring produced and offspring surviving to breeding age during two out of three years examined. Together, our results imply that variation in glucocorticoid hormones is more linked to reproductive challenge than to the costs of group living. Most generally, our study provided independent support to the cort-adaptation hypothesis, according to which reproductive effort is a major determinant, yet temporally variable, influence on cort-fitness covariation.

High regeneration capacity helps tropical seeds to counter rodent predation.

Rapid germination of non-dormant seeds is one adaptation plants have evolved to counter seed predation by rodents. Some rodent species have evolved behaviors that prevent or slow the seed germination process through seed embryo removal or seed pruning; however, no plant species is known to have successfully escaped embryo removal or seed pruning by rodents. Here, we report that the non-dormant seeds of Pittosporopsis kerrii Craib in tropical rain forests in China have a high regeneration capacity to counter seed pruning by rodents. We found seed pruning, instead of embryo removal, was commonly used by rodents to increase food storage time by slowing down the seed germination process, but that P. kerrii seeds have a high regeneration capacity to escape seed predation by rodents: all pruned seeds, pruned roots and embryo-removed seeds by rodents or people retain the ability to develop into seedlings. Seeds of P. kerrii also have other capacities (i.e. rapid seed decomposition and indigestible dormant taproots) to escape predation by reducing the plant's attractiveness to rodents. The association between seed pruning behavior in rodents and high regeneration capacity of pruned seeds or roots in P. kerrii seeds are likely novel adaptation strategies adopted by seeds and rodents, respectively.

Native herbivore exerts contrasting effects on fire regime and vegetation structure.

Although native herbivores can alter fire regimes by consuming herbaceous vegetation that serves as fine fuel and, less commonly, accumulating fuel as nest material and other structures, simultaneous considerations of contrasting effects of herbivores on fire have scarcely been addressed. We proposed that a colonial rodent, vizcacha (Lagostomus maximus), reduces and increases fire intensity at different stages in its population cycle in the semiarid scrub of Argentina. Specifically, we hypothesized that, when colonies are active, vizcachas create natural fire-breaks through intense grazing, generating over time patches of large unburned shrubs in grazed zones. In contrast, when colonies are abandoned, recovery of fine fuels and previous accumulation of coarse wood on colonies during territorial displays increases fire intensity, creating patches of high shrub mortality. To test these hypotheses, we estimated stem age of the dominant shrub (Larrea divaricata) and measured aboveground biomass in zones actively grazed by vizcachas and in ungrazed zones, and compared densities of live and dead shrubs on abandoned colonies and adjacent zones following fire. In active colonies, age and biomass of shrubs were much greater in grazed than ungrazed zones. In abandoned colonies that had been burnt, density of dead, burned shrubs was higher and density of live shrubs was lower than in adjacent zones. These results support our hypotheses and reveal a new interaction between native herbivores and fire, in which herbivores augment fire intensity by gathering fuel. Our findings indicate that, through opposing effects on fire, native herbivores enhance the heterogeneity of vegetation in woody-dominated ecosystems.

Category learning in rodents using touchscreen-based tasks.

Categorization is a fundamental cognitive function that organizes our experiences into meaningful "chunks." This category knowledge can then be generalized to novel stimuli and situations. Multiple clinical populations, including people with Parkinson's disease, amnesia, autism, ADHD and schizophrenia, have impairments in the acquisition and use of categories. Although rodent research is well suited for examining the neural mechanisms underlying cognitive functions, many rodent cognitive tasks have limited translational value. To bridge this gap, we use touchscreens to permit greater flexibility in stimulus presentation and task design, track key dependent measures, and minimize experimenter involvement. Touchscreens offer a valuable tool for creating rodent cognitive tasks that are directly comparable to tasks used with humans. Touchscreen tasks are also readily used with cutting-edge neuroscientific methods that are difficult to do in humans such as optogenetics, chemogenetics, neurophysiology and calcium imaging (using miniscopes). In this review, we show advantages of touchscreen-based tasks for studying category learning in rats. We also address multiple factors for consideration when designing category learning tasks, including the limitations of the rodent visual system, experimental design, and analysis strategies.

A framework to identify structured behavioral patterns within rodent spatial trajectories.

Animal behavior is highly structured. Yet, structured behavioral patterns-or "statistical ethograms"-are not immediately apparent from the full spatiotemporal data that behavioral scientists usually collect. Here, we introduce a framework to quantitatively characterize rodent behavior during spatial (e.g., maze) navigation, in terms of movement building blocks or motor primitives. The hypothesis that we pursue is that rodent behavior is characterized by a small number of motor primitives, which are combined over time to produce open-ended movements. We assume motor primitives to be organized in terms of two sparsity principles: each movement is controlled using a limited subset of motor primitives (sparse superposition) and each primitive is active only for time-limited, time-contiguous portions of movements (sparse activity). We formalize this hypothesis using a sparse dictionary learning method, which we use to extract motor primitives from rodent position and velocity data collected during spatial navigation, and successively to reconstruct past trajectories and predict novel ones. Three main results validate our approach. First, rodent behavioral trajectories are robustly reconstructed from incomplete data, performing better than approaches based on standard dimensionality reduction methods, such as principal component analysis, or single sparsity. Second, the motor primitives extracted during one experimental session generalize and afford the accurate reconstruction of rodent behavior across successive experimental sessions in the same or in modified mazes. Third, in our approach the number of motor primitives associated with each maze correlates with independent measures of maze complexity, hence showing that our formalism is sensitive to essential aspects of task structure. The framework introduced here can be used by behavioral scientists and neuroscientists as an aid for behavioral and neural data analysis. Indeed, the extracted motor primitives enable the quantitative characterization of the complexity and similarity between different mazes and behavioral patterns across multiple trials (i.e., habit formation). We provide example uses of this computational framework, showing how it can be used to identify behavioural effects of maze complexity, analyze stereotyped behavior, classify behavioral choices and predict place and grid cell displacement in novel environments.

Critical mass: The rise of a touchscreen technology community for rodent cognitive testing.

The rise in the number of users and institutions utilizing the rodent touchscreen technology for cognitive testing over the past decade has prompted the need for knowledge mobilization and community building. To address the needs of the growing touchscreen community, the first international touchscreen symposium was hosted at Western University. Attendees from around the world attended talks from expert neuroscientists using touchscreens to examine a vast array of questions regarding cognition and the nervous system. In addition to the symposium, a subset of attendees was invited to partake in a hands-on training course where they received touchscreen training covering both hardware and software components. Beyond the two touchscreen events, virtual platforms have been developed to further support touchscreen users: (a) Mousebytes.ca, which includes a data repository of rodent touchscreen tasks, and (b) Touchscreencognition.org, an online community with numerous training and community resources, perhaps most notably a forum where members can ask and answer questions. The advantages of the rodent touchscreen technology for cognitive neuroscience research has allowed neuroscientists from diverse backgrounds to test specific cognitive processes using well-validated and standardized apparatus, contributing to its rise in popularity and its relevance to modern neuroscience research. The commitment of the touchscreen community to data, task development and information sharing not only ensures an expansive future of the use of rodent touchscreen technology but additionally, quality research that will increase translation from preclinical studies to clinical successes.

Habitat selection in natural and human-modified landscapes by capybaras (Hydrochoerus hydrochaeris), an important host for Amblyomma sculptum ticks.

Human activities are changing landscape structure and function globally, affecting wildlife space use, and ultimately increasing human-wildlife conflicts and zoonotic disease spread. Capybaras (Hydrochoerus hydrochaeris) are linked to conflicts in human-modified landscapes (e.g. crop damage, vehicle collision), as well as the spread and amplification of Brazilian spotted fever (BSF), the most human-lethal tick-borne disease in the world. Even though it is essential to understand the link between capybaras, ticks and BSF, many knowledge gaps still exist regarding the effects of human disturbance in capybara space use. Here, we analyzed diurnal and nocturnal habitat selection strategies of capybaras across natural and human-modified landscapes using resource selection functions (RSF). Selection for forested habitats was higher across human-modified landscapes, mainly during day- periods, when compared to natural landscapes. Across natural landscapes, capybaras avoided forests during both day- and night periods. Water was consistently selected across both landscapes, during day- and nighttime. Distance to water was also the most important variable in predicting capybara habitat selection across natural landscapes. Capybaras showed slightly higher preferences for areas near grasses/shrubs across natural landscapes, and distance to grasses/shrubs was the most important variable in predicting capybara habitat selection across human-modified landscapes. Our results demonstrate human-driven variation in habitat selection strategies by capybaras. This behavioral adjustment across human-modified landscapes may be related to increases in A. sculptum density, ultimately affecting BSF.

Environmental enrichment and its influence on rodent offspring and maternal behaviours, a scoping style review of indices of depression and anxiety.

Environmental enrichment is a widely used experimental manipulation that consistently shows measurable effects on rodent behaviour across the lifespan. This scoping review assesses and thematically summarizes the literature of the past decade concerning the effects of environmental enrichment applied during sensitive developmental periods in rodent mothers and offspring. Maternal behaviours as well as maternal and offspring anxiety- and depressive-like behaviours are considered. Relevant terms were searched across five databases (Embase, MEDLINE, PsycINFO, PubMed, Web of Science) and articles were screened with inclusion and exclusion criteria. The remaining articles were thematically analysed. Our results suggest that a greater number of articles reviewed the impacts of environmental enrichment on offspring anxiety-like behaviour (n = 23) rather than on depressive-like behaviour (n = 11) or maternal caregiving behaviour (n = 12). Maternal anxiety- (n = 4) or depressive-like (n = 2) behaviours are not often evaluated for in enrichment studies. The main behavioural tests of anxiety that were reviewed include the elevated plus-maze, the open field test, and the light-dark box whereas those for depression included the forced swim test and the sucrose preference test. Our results yielded mixed findings and significant variation in behavioural responses across all tests. In mothers, trends of increased maternal care behaviours and decreased maternal depressive-like behaviours in enriched mothers were appreciated. Enrichment during the gestational period was identified as pivotal to creating behavioural change in mother subjects. In enriched offspring rodents, a trend towards decreased anxiety-like behaviours was observed most often. Potential confounds inherent in enrichment paradigms and relevant theories of enrichment and their relation to rodent behavioural tests are discussed.

How the enriched get richer? Experience-dependent modulation of microRNAs and the therapeutic effects of environmental enrichment.

Environmental enrichment and physical exercise have many well-established health benefits. Although these environmental manipulations are known to delay symptom onset and progression in a variety of neurological and psychiatric conditions, the mechanisms underlying these effects remain poorly understood. A notable candidate molecular mechanism is that of microRNA, a family of small noncoding RNAs that are important regulators of gene expression. Research investigating the many diverse roles of microRNAs has greatly expanded over the past decade, with several promising preclinical and clinical studies highlighting the role of dysregulated microRNA expression (in the brain, blood and other peripheral systems) in understanding the aetiology of disease. Altered microRNA levels have also been described following environmental interventions such as exercise and environmental enrichment in non-clinical populations and wild-type animals, as well as in some brain disorders and associated preclinical models. Recent studies exploring the effects of stimulating environments on microRNA levels in the brain have revealed an array of changes that are likely to have important downstream effects on gene expression, and thus may regulate a variety of cellular processes. Here we review literature that explores the differential expression of microRNAs in rodents following environmental enrichment and exercise, in both healthy control animals and preclinical models of relevance to neurological and psychiatric disorders.

Chimpanzee nest distribution and site reuse in a dry habitat: implications for early hominin ranging.

This paper reports on a 20-month study of chimpanzee nesting patterns in Issa, Ugalla, western Tanzania. Ugalla is one of the driest, most open, and seasonal habitats where chimpanzees are found. The methods used were ethoarchaeological, as the chimpanzees were not habituated and behavioural observations were rare. Systematic data on the spatial and temporal distribution of nests are presented. Places with no nests at the beginning of the study, despite being suitable for nesting, were used as controls. Similar to other chimpanzee study sites, nests were highly concentrated in some parts of the landscape. Issa chimpanzees preferred to nest on slopes. They extensively used the woodland vegetation type of their habitat for nesting throughout the annual cycle. Ninety percent of nest sites were used repeatedly throughout the study period, but none of the control places had nests during this period. The results indicate that chimpanzees ranged more widely during the dry season, when food abundance was lowest, food was available mainly in open vegetation types, and when drinking water was restricted to a few sources. Early hominins in similar habitats may have followed the ranging strategy of Issa chimpanzees. As with a previous study, the distribution of nests was spatially similar to archaeological distributions in early hominin sites. Hominin topography and vegetation type preferences may be misrepresented in the archaeological record. Nest sites may have been the antecedents of carcass processing sites.

Shrub cover homogenizes small mammals' activity and perceived predation risk.

Altered disturbance regimes, increasing atmospheric CO2, and other processes have increased woody cover and homogenized vegetation in savannas across the planet. African savannas with extensive versus minimal woody cover often have vastly different animal communities. However, we lack a clear mechanistic understanding of why animal communities are changing with vegetation structure. Our goal for this study was to understand how vegetation structure in an African savanna shaped the perceived predation risk of small mammals, hence affecting their activity. Using a reciprocal measure of standard giving-up-densities, amount of food eaten, we found sharp declines in rodents' perceived predation risk and increased rodent activity underneath shrub cover. This response was consistent across species; however, species showed subtle differences in their responses to grassy vegetation. Our findings suggest that areas of minimal or extensive shrub cover (shrub encroachment) may be homogenizing rodents' perceptions of predation risk and thus shaping their use of space.

High frequency audible calls in northern birch mice Sicista betulina in response to handling: effects of individuality, sex and body mass on the acoustics.

OBJECTIVES: This is the first study of the sonic and ultrasonic vocalization in a Dipodidae rodent. For the small-sized quadrupedal northern birch mouse Sicista betulina, phylogenetically related to the bipedal jerboas (Dipodidae), we report null results for ultrasonic vocalization and investigate the acoustic cues to individual identity, sex and body size in the discomfort-related high-frequency tonal sonic calls. RESULTS: We used a parallel audio recording in the sonic and ultrasonic ranges during weighting adult northern birch mice before the scheduled hibernation in captivity. The sonic (audible) high-frequency tonal calls (ranging from 6.21 to 9.86 kHz) were presented in all individuals (7 males and 4 females). The ultrasonic calls lacked in the recordings. Two-way nested ANOVA revealed the effects of caller individual identity on all 10 measured acoustic variables and the effects of sex on four out of 10 measured acoustic variables. Discriminant function analyses with 10 acoustic variables included in the analysis showed 85.5% correct assignment of calls to individual and 79.7% correct assignment of calls to sex; both values significantly exceeded the random values (23.1% and 54.3%, respectively) calculated with randomization procedure. Body mass did not differ between sexes and did not correlate significantly with the acoustic variables.

Recent Updates in Modeling Risky Decision Making in Rodents.

Excessive preference for risky over safe options is a hallmark of several psychiatric disorders. Here we describe a behavioral task that models such risky decision making in rats. In this task, rats are given choices between small, safe rewards and large rewards accompanied by risk of footshock punishment. The risk of punishment changes within a test session, allowing quantification of decision making at different levels of risk. Importantly, this task can yield a wide degree of reliable individual variability, allowing the characterization of rats as "risk-taking" or "risk-averse." The task has been demonstrated to be effective for testing the effects of pharmacological agents and neurobiological manipulations, and the individual variability (which mimics the human population) allows assessment of behavioral and neurobiological distinctions among subjects based on their risk-taking profile.