Mild early life stress enhances prefrontal-dependent response inhibition in monkeys

Neurobiology and systems biology of stress resilience

Stress resilience is the phenomenon that some people maintain their mental health despite exposure to adversity or show only temporary impairments followed by quick recovery. Resilience research attempts to unravel the factors and mechanisms that make resilience possible and to harness its insights for the development of preventative interventions in individuals at risk for acquiring stress-related dysfunctions. Biological resilience research has been lagging behind the psychological and social sciences but has seen a massive surge in recent years. At the same time, progress in this field has been hampered by methodological challenges related to finding suitable operationalizations and study designs, replicating findings, and modeling resilience in animals. We embed a review of behavioral, neuroimaging, neurobiological, and systems biological findings in adults in a critical methods discussion. We find preliminary evidence that hippocampus-based pattern separation and prefrontal-based cognitive control functions protect against the development of pathological fears in the aftermath of singular, event-type stressors [as found in fear-related disorders, including simpler forms of posttraumatic stress disorder (PTSD)] by facilitating the perception of safety. Reward system-based pursuit and savoring of positive reinforcers appear to protect against the development of more generalized dysfunctions of the anxious-depressive spectrum resulting from more severe or longer-lasting stressors (as in depression, generalized or comorbid anxiety, or severe PTSD). Links between preserved functioning of these neural systems under stress and neuroplasticity, immunoregulation, gut microbiome composition, and integrity of the gut barrier and the blood-brain barrier are beginning to emerge. On this basis, avenues for biological interventions are pointed out.

Impacts of illegal trade on socio-emotional and behavioural skills in macaques

Decades of research have illuminated the consequences of early adverse rearing experiences in laboratory macaque populations. However, limited knowledge exists about the impact of traumatic episodes in non-laboratory environments. This study delves into the repercussions of illegal trade on socio-emotional and behavioural skills in five macaque species, all victims of poaching. We categorised their past experiences into seven aspects, encompassing maternal care and interactions with conspecifics. We assessed social engagement and cooperation by analysing social behaviours and employing the Social Responsiveness Scale. Emotional resilience was evaluated by measuring anxiety levels and the occurrence of abnormal behaviours, supported by a welfare questionnaire. Additionally, the introduction of Cattell's 16PF questionnaire in macaques for the first time aimed to reveal the influence of traumatic experiences on their personality traits. Our findings emphasise the significance of early social exposure. The lack of juvenile social contact predicts reduced social behaviours and an inclination towards social avoidance in adulthood. Macaques raised by humans tend to exhibit more abnormal behaviours in social contexts, compromising their welfare. Deprivation of social exposure in infancy negatively impacts psychological stimulation and overall welfare. The duration of time spent in illegal trade correlates with heightened anxiety levels. Personality traits such as 'Calmness' and 'Unfriendliness' are influenced by rearing conditions, with macaques deprived of social interaction during their early years showing higher levels of introversion. In conclusion, the absence of social exposure during early life and hand-rearing due to illegal trade significantly shape macaques' personality traits and their social and emotional skills.

Potential resilience treatments for orangutans (Pongo spp.): Lessons from a scoping review of interventions in humans and other animals

Wild orangutans (Pongo spp.) rescued from human-wildlife conflict must be adequately rehabilitated before being returned to the wild. It is essential that released orangutans are able to cope with stressful challenges such as food scarcity, navigating unfamiliar environments, and regaining independence from human support. Although practical skills are taught to orangutans in rehabilitation centres, post-release survival rates are low. Psychological resilience, or the ability to 'bounce back' from stress, may be a key missing piece of the puzzle. However, there is very little knowledge about species-appropriate interventions which could help captive orangutans increase resilience to stress. This scoping review summarises and critically analyses existing human and non-human animal resilience literature and provides suggestions for the development of interventions for orangutans in rehabilitation. Three scientific databases were searched in 2021 and 2023, resulting in 63 human studies and 266 non-human animal studies. The first section brings together human resilience interventions, identifying common themes and assessing the applicability of human interventions to orangutans in rehabilitation. The second section groups animal interventions into categories of direct stress, separation stress, environmental conditions, social stress, and exercise. In each category, interventions are critically analysed to evaluate their potential for orangutans in rehabilitation. The results show that mild and manageable forms of intervention have the greatest potential benefit with the least amount of risk. The study concludes by emphasising the need for further investigation and experimentation, to develop appropriate interventions and measure their effect on the post-release survival rate of orangutans.

Detour test performance of cloned minipigs from three different clone populations

Genetics, the uterine environment, maternal behavior, and rearing conditions can all influence animal behavioral phenotypes. Some studies on cloned pigs have found no differences between the behavioral patterns of cloned and non-cloned animals. Other studies conducted on dogs have reported similarities in the behavior of cloned subjects. This study evaluated the performance of 12 cloned minipigs from three different clone populations (A, B, C) in a detour test around symmetric and asymmetric barriers. We measured the detour time and patterns, in order to investigate the pigs' cognitive abilities.The detour time and the detour entry/exit pattern were recorded. All the animals tended to keep a fixed entry/exit pattern instead of modifying it to accommodate changes in the working set. Significant differences in detour time were found among the populations, with animals belonging to population B being faster than the others, and also within each population.Our study is one of the few to assess the cognitive abilities of cloned minipigs. The results indicate that even animals belonging to the same cloned population may develop different cognitive, hence behavioral characteristics. Whether cloning can be utilized to obtain similar behavioral phenotypes therefore remains a matter of debate.

Tales from the life and lab of a female social neuroscientist

This narrative review charts my unconventional path to becoming a social neuroscientist and describes my research findings - some baffling, some serendipitous, some pivotal - in the field of neuropeptide biology. I trace my childhood as a Bell Labs "brat" to my adolescence as a soccer-playing party girl, to my early days as a graduate student, when I first encountered oxytocin and vasopressin. These two molecules instantly captivated - and held - my attention and imagination. For more than 25 years, a core goal of my research program has been to better understand how these neuropeptides regulate social functioning across a range of species (e.g., meadow voles, mice, squirrel monkeys, rhesus monkeys, and humans), and to translate fundamental insights from this work to guide development of novel pharmacotherapies to treat social impairments in clinical populations. I also discuss my experience of being a woman and a mother in STEM, and identify the important people and events which helped shape my career and the scientist I am today.

The Effect of Early Neurological Stimulation on Puppy Welfare in Commercial Breeding Kennels

Throughout their lives, dogs may experience various stressful events. Early neurological stimulation (ENS), which was shown to alter stress responses beneficially in some animals, has not been fully explored in dogs. Seventy-six small-breed puppies from one commercial breeding kennel were divided into three treatment groups: ENS, held, and control. Puppies in the ENS group received 30 s of handling exercises for 21 days after birth; puppies in the held group were simply held for the same amount of time. Puppies in the control group were managed as per normal breeder practices (i.e., routine husbandry and physical health checks). Physical health was assessed weekly, and puppies were generally healthy and clean. Behavioral responses to stranger approach and isolation tests were evaluated pre- and post-ground-transportation to a distributor. Puppies were more affiliative toward a stranger post-isolation than pre-isolation (p < 0.001), and post-transport than pre-transport (p < 0.001). At the distributor, puppies in the isolation test spent less time in exploratory locomotion (p < 0.001) and vocalized more than at the breeder’s kennel (p = 0.011). Treatment did not affect these results. Overall, the results suggest that the type of ENS used in this study may not provide the purported benefits to puppies’ stress responses in commercial breeding populations.

Impact of Early Life Stress on Reward Circuit Function and Regulation

Early life stress - including experience of child maltreatment, neglect, separation from or loss of a parent, and other forms of adversity - increases lifetime risk of mood, anxiety, and substance use disorders. A major component of this risk may be early life stress-induced alterations in motivation and reward processing, mediated by changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Here, we review evidence of the impact of early life stress on reward circuit structure and function from human and animal models, with a focus on the NAc. We then connect these results to emerging theoretical models about the indirect and direct impacts of early life stress on reward circuit development. Through this review and synthesis, we aim to highlight open research questions and suggest avenues of future study in service of basic science, as well as applied insights. Understanding how early life stress alters reward circuit development, function, and motivated behaviors is a critical first step toward developing the ability to predict, prevent, and treat stress-related psychopathology spanning mood, anxiety, and substance use disorders.

Long-term effects of intermittent early life stress on primate prefrontal-subcortical functional connectivity

Correlational studies of humans suggest that exposure to early life stress has long-term effects on neural circuits involved in vulnerability and resilience to mental health disorders. Stress-related mental health disorders are more prevalent in women than in men. Here, female squirrel monkeys are randomized to intermittently stressful (IS) social separations or a non-separated (NS) control condition conducted from 17 to 27 weeks of age. Nine years later in mid-life adulthood, resting-state functional magnetic resonance imaging was employed to parcellate prefrontal cortex (PFC). Resulting subdivisions were then used to characterize functional connectivity within PFC, and between PFC subdivisions and subcortical regions that are known to be altered by stress. Extensive hyper-connectivity of medial and orbitofrontal PFC with amygdala, hippocampus, and striatum was observed in IS compared to NS monkeys. Functional hyper-connectivity in IS monkeys was associated with previously reported indications of diminished anxiety-like behavior induced by prepubertal stress. Hyper-connectivity of PFC with amygdala and with hippocampus was also associated with increased ventral striatal dopamine D2 and/or D3 receptor (DRD2/3) availability assessed with positron emission tomography (PET) of [¹¹C]raclopride binding in adulthood. Ventral striatal DRD2/3 availability has been linked to cognitive control, which plays a key role in stress coping as an aspect of emotion regulation. These findings provide causal support for enduring neurobiological effects of early life stress and suggest novel targets for new treatments of stress-related mental health disorders.

Enhancing the Selection and Performance of Working Dogs

Dogs perform a variety of integral roles in our society, engaging in work ranging from assistance (e.g., service dogs, guide dogs) and therapy to detection (e.g., search-and-rescue dogs, explosive detection dogs) and protection (e.g., military and law enforcement dogs). However, success in these roles, which requires dogs to meet challenging behavioral criteria and to undergo extensive training, is far from guaranteed. Therefore, enhancing the selection process is critical for the effectiveness and efficiency of working dog programs and has the potential to optimize how resources are invested in these programs, increase the number of available working dogs, and improve working dog welfare. In this paper, we review two main approaches for achieving this goal: (1) developing selection tests and criteria that can efficiently and effectively identify ideal candidates from the overall pool of candidate dogs, and (2) developing approaches to enhance performance, both at the individual and population level, via improvements in rearing, training, and breeding. We summarize key findings from the empirical literature regarding best practices for assessing, selecting, and improving working dogs, and conclude with future steps and recommendations for working dog organizations, breeders, trainers, and researchers.

Prefrontal cortical thickness mediates the association between cortisol reactivity and executive function in childhood

The impact of stress hormones, such as cortisol, on the brain is proposed to contribute to differences in executive function of school-age children from impoverished backgrounds. However, the association between cortisol reactivity, prefrontal cortex, and executive function is relatively unexplored in young children. The current longitudinal study examined whether 63 children's early preschool-age (3-5 years, Time 1) and concurrent school-age (5-9 years, Time 2) salivary cortisol reactivity were associated with executive function and prefrontal cortical thickness at school-age. Two measures of cortisol reactivity were calculated: area under the curve with respect to ground (AUCg; total cortisol release) and with respect to increase (AUCi; total change in cortisol). Results demonstrated that Time 2 total cortisol release was negatively associated with executive function, Time 1 total cortisol release positively related to right middle frontal cortical thickness, and Time 2 total cortisol change was negatively associated with right inferior frontal cortical thickness. Moreover, greater right middle frontal cortical thickness mediated the association between greater Time 1 total cortisol release and lower executive function. This study provides support for an early adversity framework in which individual differences in executive function in childhood are directly related to the variations of cortisol-release and the effects on the prefrontal cortex thickness.

Moderate maternal separation mitigates the altered synaptic transmission and neuronal activation in amygdala by chronic stress in adult mice

Exposure to moderate level of stress during the perinatal period helps the organisms to cope well with stressful events in their later life, an effect known as stress inoculation. Amygdala is one of the kernel brain regions mediating stress-coping in the brain. However, little is known about whether early life stress may affect amygdala to have its inoculative effect. Here, we observed that moderate maternal separation (MS) from postnatal day 3 to day 21 (D3–21, 1 h per day) significantly alleviated the increased anxiety-like behavior induced by chronic social defeat stress (CSDS) in adulthood, suggesting an obvious inoculative effect of moderate MS. Further studies revealed that MS prevented CSDS-evoked augmentation of glutamatergic transmission onto principal neurons (PNs) in the basolateral amygdala (BLA) by inhibiting presynaptic glutamate release. By contrast, it did not affect GABAergic transmission in BLA PNs, as indicated by unaltered frequency and amplitude of miniature inhibitory postsynaptic currents (mIPSCs). Moreover, the CSDS-induced increase of neuronal excitability was also mitigated by MS in BLA PNs. In conclusion, our results suggest that MS may have its inoculative effect through alleviating the influences of later life stress on the glutamatergic transmission and neuronal activity in amygdala neurons.

Nonlinear relationship between early life stress exposure and subsequent resilience in monkeys

Retrospective correlational studies of humans suggest that moderate but not minimal or substantial early life stress exposure promotes the development of stress inoculation-induced resilience. Here we test for a nonlinear relationship between early life stress and resilience by comparing varying "doses" of early life stress. Juvenile squirrel monkeys underwent one of five treatment conditions between 17-27 weeks of age: Stress inoculation (SI) with continuous access to mother (SI + Mom; one stress element), SI without continuous access to mother (SI; two stress elements), SI without continuous access to mother and with alprazolam injection pretreatments (SI + Alz; three stress elements), SI without continuous access to mother and with vehicle injection pretreatments (SI + Veh; three stress elements), or standard housing (No SI; zero stress elements). Alprazolam was used to test whether anxiolytic medication diminished SI effects. Subjects exposed to one or two early life stressors subsequently responded with fewer indications of anxiety (e.g., decreased maternal clinging, increased object exploration, smaller cortisol increases) compared to No SI subjects. Subjects exposed to three early life stressors did not differ on most measures from one another or from No SI subjects. These findings provide empirical support for a nonlinear J-shaped relationship between early life stress exposure and subsequent resilience.

Early-life adversity and neurological disease: age-old questions and novel answers

Neurological illnesses, including cognitive impairment, memory decline and dementia, affect over 50 million people worldwide, imposing a substantial burden on individuals and society. These disorders arise from a combination of genetic, environmental and experiential factors, with the latter two factors having the greatest impact during sensitive periods in development. In this Review, we focus on the contribution of adverse early-life experiences to aberrant brain maturation, which might underlie vulnerability to cognitive brain disorders. Specifically, we draw on recent robust discoveries from diverse disciplines, encompassing human studies and experimental models. These discoveries suggest that early-life adversity, especially in the perinatal period, influences the maturation of brain circuits involved in cognition. Importantly, new findings suggest that fragmented and unpredictable environmental and parental signals comprise a novel potent type of adversity, which contributes to subsequent vulnerabilities to cognitive illnesses via mechanisms involving disordered maturation of brain 'wiring'.

Impacts of early social experience on cognitive development in infant rhesus macaques

Although much is known about the influences of early life experiences on the neurobiology and behavior of macaque models of child development, there is scant literature on cognitive development with respect to early rearing. Here, we examined the effects of rearing condition on affective reactivity and cognitive development in infant rhesus macaques. Infants were pseudo-randomly assigned to one of the two rearing conditions: nursery reared (NR, N = 32; 16 peer-reared, 16 surrogate-peer-reared) or mother-peer-reared (MPR, N = 7). During the first month of life, infants were administered the Primate Neonatal Neurobehavioral Assessment (PNNA). Beginning at 4 months old, infants were tested on cognitive tasks that assessed reward association, cognitive flexibility, and impulsivity. We found no gross cognitive differences between MPR and NR infants. However, MPR infants were more reactive than NR infants on the PNNA. Additionally, reactivity on the PNNA correlated with impulsivity, such that infants who were more reactive at 1 month of age completed fewer trials correctly on this task at 8-10 months. These findings are the first to directly compare cognitive development in MPR and NR infants, and add to the existing literature elucidating the influences of early social experience on temperament and development.

Distinct effects of early-life experience and trait aggression on cardiovascular reactivity and recovery

We previously demonstrated independent effects of early-life experience (ELE) and trait aggression (TA) on resting heart rate (HR) and mean arterial pressure (MAP) in rats. The present study examined the effects of TA and ELE on stress-evoked cardiovascular reactivity and recovery. Pups born to Wistar-Kyoto dams were exposed to daily 180-min periods of maternal separation (MS) during the first two weeks of life, and aggression was assessed in adult offspring using the resident-intruder test. Radiotelemetry was then used to record stress-evoked HR and MAP responses in response to: strobe light, novel environment, intruder rat, or restraint. Maximal HR and MAP responses were quantified as indices of reactivity, and exponential decay curves were fitted to determine decay constants as a measure of recovery. Strobe light was the weakest stressor, evoking the lowest increases in MAP and HR, which were significantly greater in MS-exposed rats irrespective of TA. In contrast, reactivity to and recovery from exposure to a novel environment or an intruder were significantly influenced by TA, but not ELE. TA animals exhibited greater reactivity in both of these paradigms, with either decreased (novel environment) or increased (intruder) recovery. Restraint stress induced the largest changes in HR and MAP with the slowest recovery, and these responses were shaped by a significant ELE x TA interaction. These data indicate that cardiovascular reactivity and recovery are influenced by ELE, TA, or ELE x TA interaction depending on stressor aversiveness as well as its physical and psychological dimensions.

Parenting and Cortisol in Infancy Interactively Predict Conduct Problems and Callous-Unemotional Behaviors in Childhood

This study examines observed maternal sensitivity, harsh-intrusion, and mental-state talk in infancy as predictors of conduct problems (CP) and callous-unemotional (CU) behaviors in middle childhood, as well as the extent to which infants' resting cortisol and cortisol reactivity moderate these associations. Using data from the Family Life Project (n = 1,292), results indicate that maternal sensitivity at 6 months predicts fewer CP at first grade, but only for infants who demonstrate high levels of cortisol reactivity. Maternal harsh intrusion predicts fewer empathic-prosocial behaviors, a component of CU behaviors, but only for infants who demonstrate high resting cortisol. Findings are discussed in the context of diathesis-stress and differential susceptibility models.

Hormonal and nutritional regulation of postnatal hypothalamic development

The hypothalamus is a key centre for regulation of vital physiological functions, such as appetite, stress responsiveness and reproduction. Development of the different hypothalamic nuclei and its major neuronal populations begins prenatally in both altricial and precocial species, with the fine tuning of neuronal connectivity and attainment of adult function established postnatally and maintained throughout adult life. The perinatal period is highly susceptible to environmental insults that, by disrupting critical developmental processes, can set the tone for the establishment of adult functionality. Here, we review the most recent knowledge regarding the major postnatal milestones in the development of metabolic, stress and reproductive hypothalamic circuitries, in the rodent, with a particular focus on perinatal programming of these circuitries by hormonal and nutritional influences. We also review the evidence for the continuous development of the hypothalamus in the adult brain, through changes in neurogenesis, synaptogenesis and epigenetic modifications. This degree of plasticity has encouraging implications for the ability of the hypothalamus to at least partially reverse the effects of perinatal mal-programming.

The detour paradigm in animal cognition

In this paper, we review one of the oldest paradigms used in animal cognition: the detour paradigm. The paradigm presents the subject with a situation where a direct route to the goal is blocked and a detour must be made to reach it. Often being an ecologically valid and a versatile tool, the detour paradigm has been used to study diverse cognitive skills like insight, social learning, inhibitory control and route planning. Due to the relative ease of administrating detour tasks, the paradigm has lately been used in large-scale comparative studies in order to investigate the evolution of inhibitory control. Here we review the detour paradigm and some of its cognitive requirements, we identify various ecological and contextual factors that might affect detour performance, we also discuss developmental and neurological underpinnings of detour behaviors, and we suggest some methodological approaches to make species comparisons more robust.

Investigating the separate and interactive associations of trauma and depression on brain structure: implications for cognition and aging

OBJECTIVE

Trauma and depression are associated with brain structural alterations; their combined effects on these outcomes are unclear. We previously reported a negative effect of trauma, independent of depression, on verbal learning and memory; less is known about underlying structural associates. We investigated separate and interactive associations of trauma and depression on brain structure.

METHODS

Adults aged 30-89 (N = 203) evaluated for depression (D+) and trauma history (T+) using structured clinical interviews were divided into 53 D+T+, 42 D+T-, 50 D-T+, and 58 D-T-. Multivariable linear regressions examined the separate and interactive associations of depression and trauma with prefrontal and temporal lobe cortical thickness composites and hippocampal volumes adjusting for age, sex, predicted verbal IQ, comorbid anxiety, and vascular risk. Significant results informed analyses of tract-based structural connectomic measures of efficiency and centrality.

RESULTS

Trauma, independent of depression, was associated with greater left prefrontal cortex (PFC) thickness, in particular the medial orbitofrontal cortex and pars orbitalis. A trauma × depression interaction was observed for the right PFC in age-stratified analyses: Older D + T+ had reduced PFC thickness compared with older D - T+ individuals. Regardless of age, trauma was associated with more left medial orbitofrontal cortex efficiency and less pars orbitalis centrality. In the T+ group, left pars orbitalis cortical thickness and centrality negatively correlated with verbal learning.

CONCLUSIONS

Trauma, independent of depression, associated with altered PFC characteristics, morphologically and in terms of structural network communication and influence. Additionally, findings suggest that there may be a combined effect of trauma and depression in older adults. Copyright © 2017 John Wiley & Sons, Ltd.

Moderate within-person variability in cortisol is related to executive function in early childhood

Lab-based experimental studies with humans and in animal models demonstrate that the relation between glucocorticoid (GC) levels and performance on measures of higher-order cognitive ability such as executive function (EF) is best described by an inverted U-shape curve. Moderate levels of GCs (cortisol/corticosterone) are associated with comparatively better performance relative to GC levels that are particularly high or low. Although findings from experimental studies are definitive and have high internal validity, the external validity of this association as an aspect of children's development is unknown. Here we analyze data from the Family Life Project (N=1292), a prospective longitudinal sample of children and families in predominantly low-income and rural communities followed longitudinally from infancy through age 60 months. Consistent with the prior experimental literature, we found evidence of an inverted-U relation. For children with relatively low cortisol levels, on average, between the ages 7, 15, 24, and 48 months, those illustrating moderate fluctuations in their cortisol levels over this span tended to show subsequently better EF performance at 60 months, than did children with either highly stable or highly variable temporal profiles. This curvilinear function did not extend to children whose cortisol levels were high, on average. These children tended to show lower EF performance, irrespective the stability of their cortisol levels over time.

Measures of Dogs' Inhibitory Control Abilities Do Not Correlate across Tasks

Inhibitory control, the ability to overcome prepotent but ineffective behaviors, has been studied extensively across species, revealing the involvement of this ability in many different aspects of life. While various different paradigms have been created in order to measure inhibitory control, only a limited number of studies have investigated whether such measurements indeed evaluate the same underlying mechanism, especially in non-human animals. In humans, inhibitory control is a complex construct composed of distinct behavioral processes rather than of a single unified measure. In the current study, we aimed to investigate the validity of inhibitory control paradigms in dogs. Sixty-seven dogs were tested in a battery consisting of frequently used inhibitory control tests. Additionally, dog owners were asked to complete an impulsivity questionnaire about their dog. No correlation of dogs' performance across tasks was found. In order to understand whether there are some underlying behavioral aspects explaining dogs' performance across tests, we performed principle component analyses. Results revealed that three components (persistency, compulsivity and decision speed) explained the variation across tasks. The questionnaire and dogs' individual characteristics (i.e., age and sex) provided only limited information for the derived components. Overall, results suggest that no unique measurement for inhibitory control exists in dogs, but tests rather measure different aspects of this ability. Considering the context-specificity of inhibitory control in dogs and most probably also in other non-human animals, extreme caution is needed when making conclusions about inhibitory control abilities based on a single test.

Cortisol in Neonatal Mother's Milk Predicts Later Infant Social and Cognitive Functioning in Rhesus Monkeys

Milk provides not only the building blocks for somatic development but also the hormonal signals that contribute to the biopsychological organization of the infant. Among mammals, glucocorticoids (GCs) in mother's milk have been associated with infant temperament. This study extended prior work to investigate rhesus monkey (Macaca mulatta) mother-infant dyads (N = 34) from birth through 8 months postpartum. Regression analysis revealed that cortisol concentrations in milk during the neonatal period predicted impulsivity on a cognitive task, but not global social behaviors, months later. During this time period, sex-differentiated social behavior emerged. For female infants, milk cortisol concentrations predicted total frequency of play. Collectively, these findings support and extend the "lactational programming" hypothesis on the impact of maternal-origin hormones ingested via milk.

Consequences of early adverse rearing experience(EARE) on development: insights from non-human primate studies

Early rearing experiences are important in one's whole life, whereas early adverse rearing experience(EARE) is usually related to various physical and mental disorders in later life. Although there were many studies on human and animals, regarding the effect of EARE on brain development, neuroendocrine systems, as well as the consequential mental disorders and behavioral abnormalities, the underlying mechanisms remain unclear. Due to the close genetic relationship and similarity in social organizations with humans, non-human primate(NHP) studies were performed for over 60 years. Various EARE models were developed to disrupt the early normal interactions between infants and mothers or peers. Those studies provided important insights of EARE induced effects on the physiological and behavioral systems of NHPs across life span, such as social behaviors(including disturbance behavior, social deficiency, sexual behavior, etc), learning and memory ability, brain structural and functional developments(including influences on neurons and glia cells, neuroendocrine systems, e.g., hypothalamic-pituitary-adrenal(HPA) axis, etc). In this review, the effects of EARE and the underlying epigenetic mechanisms were comprehensively summarized and the possibility of rehabilitation was discussed.

Effects of early life stress on depression, cognitive performance and brain morphology

BACKGROUND

Childhood early life stress (ELS) increases risk of adulthood major depressive disorder (MDD) and is associated with altered brain structure and function. It is unclear whether specific ELSs affect depression risk, cognitive function and brain structure.

METHOD

This cross-sectional study included 64 antidepressant-free depressed and 65 never-depressed individuals. Both groups reported a range of ELSs on the Early Life Stress Questionnaire, completed neuropsychological testing and 3T magnetic resonance imaging (MRI). Neuropsychological testing assessed domains of episodic memory, working memory, processing speed and executive function. MRI measures included cortical thickness and regional gray matter volumes, with a priori focus on the cingulate cortex, orbitofrontal cortex (OFC), amygdala, caudate and hippocampus.

RESULTS

Of 19 ELSs, only emotional abuse, sexual abuse and severe family conflict independently predicted adulthood MDD diagnosis. The effect of total ELS score differed between groups. Greater ELS exposure was associated with slower processing speed and smaller OFC volumes in depressed subjects, but faster speed and larger volumes in non-depressed subjects. In contrast, exposure to ELSs predictive of depression had similar effects in both diagnostic groups. Individuals reporting predictive ELSs exhibited poorer processing speed and working memory performance, smaller volumes of the lateral OFC and caudate, and decreased cortical thickness in multiple areas including the insula bilaterally. Predictive ELS exposure was also associated with smaller left hippocampal volume in depressed subjects.

CONCLUSIONS

Findings suggest an association between childhood trauma exposure and adulthood cognitive function and brain structure. These relationships appear to differ between individuals who do and do not develop depression.

A developmentally informed perspective on the relation between stress and psychopathology: when the problem with stress is that there is not enough

A common tenet of several prominent theories of stress and psychopathology (e.g., stress exposure) is that experiencing high rates of life stressors is associated with greater risk for negative mental health outcomes. Although there has been substantial empirical support for this position, another possibility that has received considerably less attention to date is that early life stressors may share a curvilinear rather than monotonic relation with psychological well-being. In what has been termed the "steeling effect," "stress inoculation," and "antifragility," exposure to moderate stressors early in life may confer resilience to potential detrimental effects of later stressors. An interesting implication of this model is that low levels of early life stressors, relative to normatively moderate rates, may be associated with greater sensitivity to future stressors. The present article reviews preliminary evidence consistent with this possibility, drawing on behavioral and neurobiological studies in animal models, and the more modest literature on neurocognitive, psychological, and psychophysiological functioning in humans. Limitations of the clinical literature and possible directions for future research are discussed, including naturalistic longitudinal studies with clinical outcomes, and for research examining moderators and mechanisms, across multiple levels of analysis (e.g., cognitive, immunological, and neurobiological).

Striatal dopamine D2/3 receptor regulation by stress inoculation in squirrel monkeys

Intermittent mildly stressful situations provide opportunities to learn, practice, and improve coping in a process called stress inoculation. Stress inoculation also enhances cognitive control and response inhibition of impulsive motivated behavior. Cognitive control and motivation have been linked to striatal dopamine D2 and/or D3 receptors (DRD2/3) in rodents, monkeys, and humans. Here, we study squirrel monkeys randomized early in life to stress inoculation with or without maternal companionship and a no-stress control treatment condition. Striatal DRD2/3 availability in adulthood was measured in vivo by [¹¹C]raclopride binding using positron emission tomography (PET). DRD2/3 availability was greater in caudate and putamen compared to ventral striatum as reported in PET studies of humans and other non-human primates. DRD2/3 availability in ventral striatum was also consistently greater in stress inoculated squirrel monkeys compared to no-stress controls. Squirrel monkeys exposed to stress inoculation in the presence of their mother did not differ from squirrel monkeys exposed to stress inoculation without maternal companionship. Similar effects in different social contexts extend the generality of our findings and together suggest that stress inoculation increases striatal DRD2/3 availability as a correlate of cognitive control in squirrel monkeys.

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Stress inoculation entails intermittent exposure to mildly stressful situations.

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Stress inoculation promotes coping, emotion regulation, and cognitive control of behavior.

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Cognitive control has been linked to striatal dopamine D2/3 receptors (DRD2/3).

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Stress inoculation increases striatal DRD2/3 availability and enhances cognitive control in squirrel monkeys.

Early-life Social Adversity and Developmental Processes in Nonhuman Primates

Most primate species produce offspring that are altricial and highly dependent upon caregivers. As a consequence, a host of developmental trajectories can be dramatically altered by variation in early experiences. We review the impact of early social experiences (in both experimental models and natural contexts) on developmental profiles in three species of nonhuman primates: marmosets, squirrel monkeys, and macaques. Graded exposure to early-life social adversity (ELSA) produces short- to long-term effects on multiple developmental outcomes, including affect, social behavior, cognitive and attentional processes, and in the neural substrates that underlie these sociobehavioral traits.

Maternal effects on offspring stress physiology in wild chimpanzees

Early life experiences are known to influence hypothalamic-pituitary-adrenal (HPA) axis development, which can impact health outcomes through the individual's ability to mount appropriate physiological reactions to stressors. In primates, these early experiences are most often mediated through the mother and can include the physiological environment experienced during gestation. Here, we investigate stress physiology of dependent offspring in wild chimpanzees for the first time and examine whether differences in maternal stress physiology are related to differences in offspring stress physiology. Specifically, we explore the relationship between maternal rank and maternal fecal glucocorticoid metabolite (FGM) concentration during pregnancy and early lactation (first 6 months post-partum) and examine whether differences based on maternal rank are associated with dependent offspring FGM concentrations. We found that low-ranking females exhibited significantly higher FGM concentrations during pregnancy than during the first 6 months of lactation. Furthermore, during pregnancy, low-ranking females experienced significantly higher FGM concentrations than high-ranking females. As for dependent offspring, we found that male offspring of low-ranking mothers experienced stronger decreases in FGM concentrations as they aged compared to males with high-ranking mothers or their dependent female counterparts. Together, these results suggest that maternal rank and FGM concentrations experienced during gestation are related to offspring stress physiology and that this relationship is particularly pronounced in males compared to females. Importantly, this study provides the first evidence for maternal effects on the development of offspring HPA function in wild chimpanzees, which likely relates to subsequent health and fitness outcomes. Am. J. Primatol. 80:e22525, 2018. © 2016 Wiley Periodicals, Inc.

Seeding Stress Resilience through Inoculation

Stress is a generalized set of physiological and psychological responses observed when an organism is placed under challenging circumstances. The stress response allows organisms to reattain the equilibrium in face of perturbations. Unfortunately, chronic and/or traumatic exposure to stress frequently overwhelms coping ability of an individual. This is manifested as symptoms affecting emotions and cognition in stress-related mental disorders. Thus environmental interventions that promote resilience in face of stress have much clinical relevance. Focus of the bulk of relevant neurobiological research at present remains on negative aspects of health and psychological outcomes of stress exposure. Yet exposure to the stress itself can promote resilience to subsequent stressful episodes later in the life. This is especially true if the prior stress occurs early in life, is mild in its magnitude, and is controllable by the individual. This articulation has been referred to as "stress inoculation," reminiscent of resilience to the pathology generated through vaccination by attenuated pathogen itself. Using experimental evidence from animal models, this review explores relationship between nature of the "inoculum" stress and subsequent psychological resilience.

Therapeutic implications of the choroid plexus-cerebrospinal fluid interface in neuropsychiatric disorders

The choroid plexus (CP) comprises an epithelial monolayer that forms an important physical, enzymatic and immunologic barrier, called the blood-cerebrospinal fluid barrier (BCSFB). It is a highly vascularized organ located in the brain ventricles that is key in maintaining brain homeostasis as it produces cerebrospinal fluid (CSF) and has other important secretory functions. Furthermore, the CP-CSF interface plays a putative role in neurogenesis and has been implicated in neuropsychiatric diseases such as the neurodevelopmental disorders schizophrenia and autism. A role for this CNS border was also implicated in sleep disturbances and chronic and/or severe stress, which are risk factors for the development of neuropsychiatric conditions. Understanding the mechanisms by which disturbance of the homeostasis at the CP-CSF interface is involved in these different chronic low-grade inflammatory diseases can give new insights into therapeutic strategies. Hence, this review discusses the different roles that have been suggested so far for the CP in these neuropsychiatric disorders, with special attention to potential therapeutic applications.

Increasing arousal enhances inhibitory control in calm but not excitable dogs

The emotional-reactivity hypothesis proposes that problem-solving abilities can be constrained by temperament, within and across species. One way to test this hypothesis is with the predictions of the Yerkes-Dodson law. The law posits that arousal level, a component of temperament, affects problem solving in an inverted U-shaped relationship: Optimal performance is reached at intermediate levels of arousal and impeded by high and low levels. Thus, a powerful test of the emotional-reactivity hypothesis is to compare cognitive performance in dog populations that have been bred and trained based in part on their arousal levels. We therefore compared a group of pet dogs to a group of assistance dogs bred and trained for low arousal (N = 106) on a task of inhibitory control involving a detour response. Consistent with the Yerkes-Dodson law, assistance dogs, which began the test with lower levels of baseline arousal, showed improvements when arousal was artificially increased. In contrast, pet dogs, which began the test with higher levels of baseline arousal, were negatively affected when their arousal was increased. Furthermore, the dogs' baseline levels of arousal, as measured in their rate of tail wagging, differed by population in the expected directions. Low-arousal assistance dogs showed the most inhibition in a detour task when humans eagerly encouraged them, while more highly aroused pet dogs performed worst on the same task with strong encouragement. Our findings support the hypothesis that selection on temperament can have important implications for cognitive performance.

Development of a cognitive testing apparatus for socially housed mother-peer-reared infant rhesus monkeys

Though cognitive testing of infant monkeys has been practiced for the past 40 years, these assessments have been limited primarily to nursery-reared infants due to the confounds of separating mother-reared infants for assessments. Here, we describe a pilot study in which we developed a cognitive testing apparatus for socially housed, mother-peer-reared rhesus macaques under 1 year of age (Macaca mulatta) that allowed the infants to freely return to their mothers for contact comfort. Infants aged 151.2 ± 18.3 days (mean ± SEM; n = 5) were trained and tested on an object detour reach task. Infants completed training in 5.0 ± 0.2 days, and completed testing in 6.2 ± 0.9 days. Across 4 days of testing, infants improved to nearly errorless performance (Friedman test: χ(2)  = 13.27, df = 3, p = 0.004) and learned to do the task more quickly (Friedman test: χ(2)  = 11.69, df = 3, p = 0.009). These are the first cognitive data in group-housed, mother-peer-reared rhesus monkeys under 1 year of age, and they underscore the utility of this apparatus for studying cognitive development in a normative population of infant monkeys.

The Impact of Developmental Timing for Stress and Recovery

Stress can have lasting effects on the brain and behavior. Delineating the impact of stress on the developing brain is fundamental for understanding mechanisms through which stress induces persistent effects on behavior that can lead to psychopathology. The growing field of translational developmental neuroscience has revealed a significant role of the timing of stress on risk, resilience, and neuroplasticity. Studies of stress across species have provided essential insight into the mechanisms by which the brain changes and the timing of those changes on outcome. In this article, we review the neurobiological effects of stress and propose a model by which sensitive periods of neural development interact with stressful life events to affect plasticity and the effects of stress on functional outcomes. We then highlight how early-life stress can alter the course of brain development. Finally, we examine mechanisms of buffering against early-life stress that may promote resilience and positive outcomes. The findings are discussed in the context of implications for early identification of risk and resilience factors and development of novel interventions that target the biological state of the developing brain to ultimately ameliorate the adverse consequences of stress during childhood and adolescence.

Peripheral and Central Mechanisms of Stress Resilience

Viable new treatments for depression and anxiety have been slow to emerge, likely owing to the complex and incompletely understood etiology of these disorders. A budding area of research with great therapeutic promise involves the study of resilience, the adaptive maintenance of normal physiology and behavior despite exposure to marked psychological stress. This phenomenon, documented in both humans and animal models, involves coordinated biological mechanisms in numerous bodily systems, both peripheral and central. In this review, we provide an overview of resilience mechanisms throughout the body, discussing current research in animal models investigating the roles of the neuroendocrine, immune, and central nervous systems in behavioral resilience to stress.

Coping and glucocorticoid receptor regulation by stress inoculation

Intermittent exposure to mildly stressful situations provides opportunities to practice coping in the context of exposure psychotherapies and stress inoculation training. Previously, we showed that stress inoculation modeled in juvenile monkeys enhances subsequent indications of resilience. Here we examine stress inoculation effects in adult female monkeys. We found that stress inoculation prevents social separation stress induced anhedonia measured using sucrose preference tests and reduces the hypothalamic pituitary adrenal (HPA) axis stress hormone response to a novel environment. Stress inoculation also increases glucocorticoid receptor (NR3C1) gene expression in anterior cingulate cortex but not hippocampus. Increased anterior cingulate cortex NR3C1 expression induced by stress inoculation is not associated with significant changes in GR1F promoter DNA methylation. On average, low levels of promoter DNA methylation and limited GR1F expression were evident in monkey anterior cingulate cortex as observed in corticolimbic brain regions of adult humans. Taken together these findings suggest that stress inoculation in adulthood enhances behavioral and hormonal aspects of coping without significantly influencing GR1F promoter DNA methylation as a mechanism for NR3C1 transcription regulation.

A mechanistic look at the effects of adversity early in life on cardiovascular disease risk during adulthood

Early origins of adult disease may be defined as adversity or challenges during early life that alter physiological responses and prime the organism to chronic disease in adult life. Adverse childhood experiences or early life stress (ELS) may be considered a silent independent risk factor capable of predicting future cardiovascular disease risk. Maternal separation (MatSep) provides a suitable model to elucidate the underlying molecular mechanisms by which ELS increases the risk to develop cardiovascular disease in adulthood. The aim of this review is to describe the links between behavioural stress early in life and chronic cardiovascular disease risk in adulthood. We will discuss the following: (i) adult cardiovascular outcomes in humans subjected to ELS, (ii) MatSep as an animal model of ELS as well as the limitations and advantages of this model in rodents and (iii) possible ELS-induced mechanisms that predispose individuals to greater cardiovascular risk. Overall, exposure to a behavioural stressor early in life sensitizes the response to a second stressor later in life, thus unmasking an exaggerated cardiovascular dysfunction that may influence quality of life and life expectancy in adulthood.

Understanding resilience

Resilience is the ability to adapt successfully in the face of stress and adversity. Stressful life events, trauma, and chronic adversity can have a substantial impact on brain function and structure, and can result in the development of posttraumatic stress disorder (PTSD), depression and other psychiatric disorders. However, most individuals do not develop such illnesses after experiencing stressful life events, and are thus thought to be resilient. Resilience as successful adaptation relies on effective responses to environmental challenges and ultimate resistance to the deleterious effects of stress, therefore a greater understanding of the factors that promote such effects is of great relevance. This review focuses on recent findings regarding genetic, epigenetic, developmental, psychosocial, and neurochemical factors that are considered essential contributors to the development of resilience. Neural circuits and pathways involved in mediating resilience are also discussed. The growing understanding of resilience factors will hopefully lead to the development of new pharmacological and psychological interventions for enhancing resilience and mitigating the untoward consequences.

Socioeconomic status and health: mediating and moderating factors

Health disparities (differences in health by socioeconomic groups) are a pressing issue in our society. This article provides an overview of a multilevel approach that seeks to understand the mechanisms underlying health disparities by considering factors at the individual, family, and neighborhood levels. In addition, we describe an approach to connecting these factors to various levels of biological processes (systemic inflammation, cellular processes, and genomic pathways) that drive disease pathophysiology. In the second half of the article, we address the question of why some low-socioeconomic-status (low-SES) individuals manage to maintain good physical health. We identify naturally occurring psychosocial factors that help buffer these individuals from adverse physiological responses and pathogenic processes leading to chronic disease. What is protective for low-SES individuals is not the same as what is protective for high-SES individuals, and this needs to be taken into account in interventions aimed at reducing health disparities.

Neurobiology of resilience

Humans exhibit a remarkable degree of resilience in the face of extreme stress, with most resisting the development of neuropsychiatric disorders. Over the past 5 years, there has been increasing interest in the active, adaptive coping mechanisms of resilience; however, in humans, most published work focuses on correlative neuroendocrine markers that are associated with a resilient phenotype. In this review, we highlight a growing literature in rodents that is starting to complement the human work by identifying the active behavioral, neural, molecular and hormonal basis of resilience. The therapeutic implications of these findings are important and can pave the way for an innovative approach to drug development for a range of stress-related syndromes.

Structural variations in prefrontal cortex mediate the relationship between early childhood stress and spatial working memory

A large corpus of research indicates that exposure to stress impairs cognitive abilities, specifically executive functioning dependent on the prefrontal cortex (PFC). We collected structural MRI scans (n = 61), well-validated assessments of executive functioning, and detailed interviews assessing stress exposure in humans to examine whether cumulative life stress affected brain morphometry and one type of executive functioning, spatial working memory, during adolescence-a critical time of brain development and reorganization. Analysis of variations in brain structure revealed that cumulative life stress and spatial working memory were related to smaller volumes in the PFC, specifically prefrontal gray and white matter between the anterior cingulate and the frontal poles. Mediation analyses revealed that individual differences in prefrontal volumes accounted for the association between cumulative life stress and spatial working memory. These results suggest that structural changes in the PFC may serve as a mediating mechanism through which greater cumulative life stress engenders decrements in cognitive functioning.

Enhanced stimulus sequence-dependent repeated learning in male offspring after prenatal stress alone or in conjunction with lead exposure

Both lead (Pb) exposure and prenatal stress (PS) can produce cognitive deficits, and in a prior study we demonstrated enhanced cognitive deficits in repeated learning of female rats exposed to both of these developmental insults (Cory-Slechta et al., 2010). However, PS can also lead to improved cognitive outcomes that are both gender- and context-dependent. Thus, the current study examined whether Pb ± PS likewise produced repeated learning deficits in males, either after maternal or lifetime Pb exposure. Repeated learning was evaluated using a multiple schedule of repeated learning and performance that required learning 3-response sequences in male offspring that had been subjected to either maternal Pb (0 or 150 ppm) or lifetime Pb exposure (0 or 50 ppm) beginning two months prior to dam breeding, to prenatal immobilization restraint stress (gestational days 16-17), or to both Pb and PS. Blood Pb, corticosterone, hippocampal glucocorticoid receptor density and brain monoamines were also measured. In contrast to outcomes in females, sequence-specific enhancements of repeated learning accuracy were produced by PS, particularly when combined with Pb, results that appeared to be more robust in combination with lifetime than maternal Pb exposure. A common behavioral mechanism of these improvements appears to be an increased reinforcement density associated with increased response rates and shorter session times seen with PS ± Pb that could shorten time to reinforcement. Trends toward lower levels of nucleus accumbens dopamine activity seen after both maternal Pb and lifetime Pb combined with PS suggest a possible role for this region/neurotransmitter in enhanced accuracy, whereas PS ± Pb-induced corticosterone changes did not exhibit an obvious systematic relationship to accuracy enhancements. While PS ± Pb-based increases in accuracy appear to be an improved outcome, the benefits of increased response rate are by no means universal, but highly context-dependent and can lead to adverse behavioral effects in other conditions.

Social influences on neuroplasticity: stress and interventions to promote well-being

Experiential factors shape the neural circuits underlying social and emotional behavior from the prenatal period to the end of life. These factors include both incidental influences, such as early adversity, and intentional influences that can be produced in humans through specific interventions designed to promote prosocial behavior and well-being. Here we review important extant evidence in animal models and humans. Although the precise mechanisms of plasticity are still not fully understood, moderate to severe stress appears to increase the growth of several sectors of the amygdala, whereas the effects in the hippocampus and prefrontal cortex tend to be opposite. Structural and functional changes in the brain have been observed with cognitive therapy and certain forms of meditation and lead to the suggestion that well-being and other prosocial characteristics might be enhanced through training.

"Shift-and-Persist" Strategies: Why Low Socioeconomic Status Isn't Always Bad for Health

Some individuals, despite facing recurrent, severe adversities in life such as low socioeconomic status (SES), are nonetheless able to maintain good physical health. This article explores why these individuals deviate from the expected association of low SES and poor health and outlines a "shift-and-persist" model to explain the psychobiological mechanisms involved. This model proposes that, in the midst of adversity, some children find role models who teach them to trust others, better regulate their emotions, and focus on their futures. Over a lifetime, these low-SES children develop an approach to life that prioritizes shifting oneself (accepting stress for what it is and adapting the self through reappraisals) in combination with persisting (enduring life with strength by holding on to meaning and optimism). This combination of shift-and-persist strategies mitigates sympathetic-nervous-system and hypothalamic-pituitary-adrenocortical responses to the barrage of stressors that low-SES individuals confront. This tendency vectors individuals off the trajectory to chronic disease by forestalling pathogenic sequelae of stress reactivity, like insulin resistance, high blood pressure, and systemic inflammation. We outline evidence for the model and argue that efforts to identify resilience-promoting processes are important in this economic climate, given limited resources for improving the financial circumstances of disadvantaged individuals.

Hypothalamic-pituitary-adrenal axis physiology and cognitive control of behavior in stress inoculated monkeys

Monkeys exposed to stress inoculation protocols early in life subsequently exhibit diminished neurobiological responses to moderate psychological stressors and enhanced cognitive control of behavior during juvenile development compared to non-inoculated monkeys. The present experiments extended these findings and revealed that stress inoculated monkeys: (a) mount neurobiological responses equivalent to non-inoculated monkeys when the stressor is of sufficient intensity, and (b) continue to exhibit enhanced cognitive control as young adults compared to non-inoculated monkeys. These results suggest that stress inoculation protocols alter the appraisal of and response to moderate stressors as less threatening and permanently enhance cognitive control, at least through early adulthood. These data therefore support the notion that the stress inoculation phenotype reflects stress resilience rather than stress pathology.

Identifying key features of early stressful experiences that produce stress vulnerability and resilience in primates

This article examines the complex role of early stressful experiences in producing both vulnerability and resilience to later stress-related psychopathology in a variety of primate models of human development. Two types of models are reviewed: Parental Separation Models (e.g., isolate-rearing, peer-rearing, parental separations, and stress inoculation) and Maternal Behavior Models (e.g., foraging demands, variation in maternal style, and maternal abuse). Based on empirical evidence, it is argued that early life stress exposure does not increase adult vulnerability to stress-related psychopathology as a linear function, as is generally believed, but instead reflects a quadratic function. Features of early stress exposure including the type, duration, frequency, ecological validity, sensory modality, and developmental timing, within and between species, are identified to better understand how early stressful experiences alter neurobiological systems to produce such diverse developmental outcomes. This article concludes by identifying gaps in our current knowledge, providing directions for future research, and discussing the translational implications of these primate models for human development and psychopathology.

Adaptive significance of natural variations in maternal care in rats: a translational perspective

A wealth of data from the last fifty years documents the potency of early life experiences including maternal care on developing offspring. A majority of this research has focused on the developing stress axis and stress-sensitive behaviors in hopes of identifying factors impacting resilience and risk-sensitivity. The power of early life experience to shape later development is profound and has the potential to increase fitness of individuals for their environments. Current findings in a rat maternal care paradigm highlight the complex and dynamic relation between early experiences and a variety of outcomes. In this review we propose adaptive hypotheses for alternate maternal strategies and resulting offspring phenotypes, and suggest means of distinguishing between these hypotheses. We also provide evidence underscoring the critical role of context in interpreting the adaptive significance of early experiences. If our goal is to identify risk-factors relevant to humans, we must better explore the role of the social and physical environment in our basic animal models.