Effects of psychosocial stress on the goal-directed and habit memory systems during learning and later execution

A dual-pathway architecture enables chronic stress to promote habit formation

Chronic stress can change how we learn and, thus, how we make decisions by promoting the formation of inflexible, potentially maladaptive, habits. Here we investigated the neuronal circuit mechanisms that enable this. Using a multifaceted approach in male and female mice, we reveal a dual pathway, amygdala-striatal, neuronal circuit architecture by which a recent history of chronic stress shapes learning to disrupt flexible goal-directed behavior in favor of inflexible habits. Chronic stress inhibits activity of basolateral amygdala projections to the dorsomedial striatum to impede the action-outcome learning that supports flexible, goal-directed decisions. Stress also increases activity in direct central amygdala projections to the dorsomedial striatum to promote the formation of rigid, inflexible habits. Thus, stress exerts opposing effects on two amygdala-striatal pathways to promote premature habit formation. These data provide neuronal circuit insights into how chronic stress shapes learning and decision making, and help understand how stress can lead to the disrupted decision making and pathological habits that characterize substance use disorders and other psychiatric conditions.

Competitive Neurocognitive Processes Following Bereavement

Bereavement is a common human experience that often involves significant impacts on psychological, emotional and even cognitive functioning. Though various psychological theories have been proposed to conceptualize the grief process, our current understanding of the underlying neurocognitive mechanisms of grief is limited. The present paper proposes a neurocognitive model to understand phenomena in typical grief, which links loss-related reactions to underlying learning and executive processes. We posit that the competitive relationship between the basal ganglia (BG) and circuitry involving the medial temporal lobe (MTL) underlies common cognitive experiences in grief such as a sense of "brain fog." Due to the intense stressor of bereavement, we suggest that these two systems' usually flexible interactive relationship become imbalanced. The resulting temporary dominance of either the BG or the MTL system is then manifested in perceived cognitive changes. Understanding the underlying neurocognitive mechanism in grief could inform ways to best support bereaved individuals.

Does stress consistently favor habits over goal-directed behaviors? Data from two preregistered exact replication studies

Instrumental learning is controlled by two distinct parallel systems: goal-directed (action-outcome) and habitual (stimulus-response) processes. Seminal research by Schwabe and Wolf (2009, 2010) has demonstrated that stress renders behavior more habitual by decreasing goal-directed control. More recent studies yielded equivocal evidence for a stress-induced shift towards habitual responding, yet these studies used different paradigms to evaluate instrumental learning or used different stressors. Here, we performed exact replications of the original studies by exposing participants to an acute stressor either before (cf. Schwabe and Wolf, 2009) or directly after (cf. Schwabe and Wolf, 2010) an instrumental learning phase in which they had learned that distinct actions led to distinct, rewarding food outcomes (i.e., instrumental learning). Then, following an outcome devaluation phase in which one of the food outcomes was consumed until participants were satiated, action-outcome associations were tested in extinction. Despite successful instrumental learning and outcome devaluation and increased subjective and physiological stress levels following stress exposure, the stress and no-stress groups in both replication studies responded indifferently to valued and devalued outcomes. That is, non-stressed participants failed to demonstrate goal-directed behavioral control, thereby rendering the critical test of a shift from goal-directed to habitual control in the stress group inapt. Several reasons for these replication failures are discussed, including the rather indiscriminate devaluation of outcomes that may have contributed to indifferent responding during extinction, which emphasize the need to further our understanding of the boundary conditions in research aimed at demonstrating a stress-induced shift towards habitual control.

Adolescent social isolation shifts the balance of decision-making strategy from goal-directed action to habitual response in adulthood via suppressing the excitatory neurotransmission onto the direct pathway of the dorsomedial striatum

Adverse experience, such as social isolation, during adolescence is one of the major causes of neuropsychiatric disorders that extend from adolescence into adulthood, such as substance addiction, obsessive-compulsive disorder, and eating disorders leading to obesity. A common behavioral feature of these neuropsychiatric disorders is a shift in the balance of decision-making strategy from goal-directed action to habitual response. This study has verified that adolescent social isolation directly shifts the balance of decision-making strategy from goal-directed action to habitual response, and that it cannot be reversed by simple regrouping. This study has further revealed that adolescent social isolation induces a suppression in the excitatory neurotransmission onto the direct-pathway medium spiny neurons of the dorsomedial striatum (DMS), and that chemogenetically compensating this suppression effect shifts the balance of decision-making strategy from habitual response back to goal-directed action. These findings suggest that the plasticity in the DMS causes the shift in the balance of decision-making strategy, which would potentially help to develop a general therapy to treat the various neuropsychiatric disorders caused by adolescent social isolation. Such a study is especially necessary under the circumstances that social distancing and lockdown have caused during times of world-wide, society-wide pandemic.

The effect of stress and exercise on the learning performance of horses

Domestic horses are widely used for physically demanding activities but the effect of exercise on their learning abilities has not been explored. Horses are also frequently exposed to stressors that may affect their learning. Stress and exercise result in the release of glucocorticoids, noradrenaline and other neurotransmitters that can influence learning. It is not currently possible to directly measure concentrations of neurotransmitters in the brains of behaving horses, however the inference of neurobiological processes from peripheral markers have been widely used in studies of human cognition. We assigned 41 horses to either ridden exercise, uncontrollable stress or inactivity and evaluated their acquisition of an industry-style aversive instrumental learning task. Exercised horses achieved the learning criterion in the fewest number of trials compared to the stressed and inactive horses whose performance did not differ. The exercised horses’ salivary cortisol concentrations decreased during learning whereas the concentrations of the other groups increased. Spearman’s correlations revealed that horses with the highest cortisol concentrations required the most trials to reach the criterion. We present novel data that exercise prior to learning may enhance the acquisition of learning in horses. Conversely, activities that expose horses to uncontrollable stressors causing strong cortisol release may impair learning. It is proposed that these effects may be due to the influence of neurotransmitters such as cortisol and noradrenaline on brain regions responsible for learning.

Dopaminergic and noradrenergic modulation of stress-induced alterations in brain activation associated with goal-directed behaviour

BACKGROUND

Acute stress is thought to reduce goal-directed behaviour, an effect purportedly associated with stress-induced release of catecholamines. In contrast, experimentally increased systemic catecholamine levels have been shown to increase goal-directed behaviour. Whether experimentally increased catecholamine function can modulate stress-induced reductions in goal-directed behaviour and its neural substrates, is currently unknown.

AIM

To assess whether and how experimentally induced increases in dopamine and noradrenaline contribute to the acute stress effects on goal-directed behaviour and associated brain activation.

METHODS

One hundred participants underwent a stress induction protocol (Maastricht acute stress test; MAST) or a control procedure and received methylphenidate (MPH) (40 mg, oral) or placebo according to a 2 × 2 between-subjects design. In a well-established instrumental learning paradigm, participants learnt stimulus-response-outcome associations, after which rewards were selectively devalued. Participants' brain activation and associated goal-directed behaviour were assessed in a magnetic resonance imaging scanner at peak cortisol/MPH concentrations.

RESULTS

The MAST and MPH increased physiological measures of stress (salivary cortisol and blood pressure), but only MAST increased subjective measures of stress. MPH modulated stress effects on activation of brain areas associated with goal-directed behaviour, including insula, putamen, amygdala, medial prefrontal cortex, frontal pole and orbitofrontal cortex. However, MPH did not modulate the tendency of stress to induce a reduction in goal-directed behaviour.

CONCLUSION

Our neuroimaging data suggest that MPH-induced increases in dopamine and noradrenaline reverse stress-induced changes in key brain regions associated with goal-directed behaviour, while behavioural effects were absent. These effects may be relevant for preventing stress-induced maladaptive behaviour like in addiction or binge eating disorder.

Attitudes, Habits, and Behavior Change

Efforts to guide peoples' behavior toward environmental sustainability, good health, or new products have emphasized informational and attitude change strategies. There is evidence that changing attitudes leads to changes in behavior, yet this approach takes insufficient account of the nature and operation of habits, which form boundary conditions for attitude-directed interventions. Integration of research on attitudes and habits might enable investigators to identify when and how behavior change strategies will be most effective. How might attitudinally driven behavior change be consolidated into lasting habits? How do habits protect the individual against the vicissitudes of attitudes and temptations and promote goal achievement? How might attitudinal approaches aiming to change habits be improved by capitalizing on habit discontinuities and strategic planning? When and how might changing or creating habit architecture shape habits directly? A systematic approach to these questions might help move behavior change efforts from attitude change strategies to habit change strategies. Expected final online publication date for the Annual Review of Psychology, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Cortisol promotes the cognitive regulation of high intensive emotions independent of timing

Failures to cognitively downregulate negative emotions are a crucial risk factor for mental disorders. Previous studies provide evidence for a stress-induced improvement of cognitive emotion regulation possibly mediated via glucocorticoid actions. Cortisol can initialize immediate non-genomic as well as delayed genomic effects on cognitive control functioning, but its distinct effects on emotion regulation processes remain to be shown. Here, we sought to characterize time-dependent effects of oral cortisol administration on cognitive emotion regulation outcomes. We expected cortisol to improve emotion regulation success. Possible interactions with the delay between cortisol treatment and emotion regulation, strategy use and intensity of the emotional stimuli were examined. Eighty-five healthy men received either 10 mg hydrocortisone or a placebo in a double-blind, randomized design 30 or 90 min prior to an emotion regulation paradigm, in which they were asked to downregulate their emotional responses towards low and high intensive negative pictures via reappraisal or distraction. Affective ratings and pupil dilation served as outcome measures. Reduced arousal, enhanced valence ratings as well as increases in pupil dilations indexing the cognitive regulatory effort indicated successful downregulation of negative emotions evoked by high intensive but not low intensive negative pictures. Cortisol significantly reduced arousal ratings when downregulating high intensive negative emotions via distraction and (at a trend level) via reappraisal, independent of timing, demonstrating a beneficial effect of cortisol on subjective regulatory outcomes. Taken together, this study provides initial evidence suggesting that cortisol promotes the cognitive control of high intensive negative emotions both, 30 and 90 min after treatment.

Rats exposed to intermittent ethanol during late adolescence exhibit enhanced habitual behavior following reward devaluation

The brain undergoes substantial maturation during adolescence, and repeated exposure to ethanol at this time has been shown to result in long-lasting behavioral and neural consequences. During the broad period of adolescence, different neuronal populations and circuits are refined between early and late adolescence, suggesting the possibility that ethanol exposure at these differing times may lead to differential outcomes. The goal of the current study was to evaluate the impact of adolescent intermittent ethanol (AIE) during early and late adolescence on the formation of goal-directed and habitual behavior in adulthood. Male and female Sprague-Dawley rats were exposed to ethanol via intragastric gavage (4.0 g/kg, 25% v/v) every other day from postnatal day (P) 25-45 or P45-65, considered early and late adolescence, respectively. In adulthood (~P70 early or ~ P90 late), rats were gradually food-restricted and began operant training on a fixed ratio 1 schedule. Rats were then transitioned onto random interval schedules and eventually underwent a sensory-specific satiation procedure as a model of reward devaluation. Few differences as a result of adolescent ethanol exposure were found during instrumental training. Following reward devaluation, rats exposed to water and ethanol during early adolescence exhibited reductions in lever pressing, suggestive of a goal-directed response pattern. In contrast, late AIE males and females demonstrated persistent responding following both devalued and non-devalued trials, findings representative of a habitual behavior pattern. The shifts from goal-directed to habitual behavior noted only following late AIE contribute to the growing literature identifying specific behavioral consequences as a result of ethanol exposure during distinct developmental periods within adolescence. More work is needed to determine whether the greater habit formation following late AIE is also associated with elevated habitual ethanol consumption.

The Kindling/Sensitization Model and Early Life Stress

INTRODUCTION

Few animal models address the characteristics of the longitudinal course of bipolar disorder. However, behavioral sensitization (to recurrent stressors and psychomotor stimulants) and kindling of seizures both provide clues to mechanisms in the progressive course of bipolar disorder.

METHODS

We describe aspects of bipolar illness that show sensitization and kindling-like increases reactivity to the recurrence of stressors, mood episodes, and bouts of substance abuse. Mechanisms of these events and clinical implications for treatment are discussed.

RESULTS

Early life stress is a risk factor for the development of episodes of unipolar depression and bipolar disorder and the acquisition of substance abuse. Initial affective episodes are often triggered by the recurrence of psychosocial stressors in adulthood, but after many episodes have occurred, episodes may also begin to emerge spontaneously in a kindling-like progression. More prior episodes are associated with faster recurrences, dysfunction, disability, frontal cortical abnormalities, cognitive impairment, shorter telomeres, treatment refractoriness, and an increased risk of a diagnosis of dementia in old age. Sensitization to stressors, episodes, and substances of abuse each appear driven by epigenetic mechanisms and their accumulation on DNA, histones, and microRNA. Patients with bipolar illness in the USA are more ill than those from Europe and experience more sensitization to stressors, episodes, substance abuse, as well as more genetic vulnerability across four generations.

DISCUSSION

The sensitization and kindling models highlight the importance of early intervention and prevention in order to limit or halt the downhill progression of bipolar disorder and its multiple comorbidities toward treatment refractoriness. Clinical data support this conclusion as well but have not been sufficient to change practice in the direction of early intervention. It is hoped that a better understanding of sensitization and kindling-like mechanisms will add neurobiological rationales for the importance of prevention and sustained prophylactic intervention in rendering bipolar disorder a more benign illness.

Inhibition of the fatty acid amide hydrolase changes behaviors and brain catecholamines in a sex-specific manner in rats exposed to chronic unpredictable stress

Sex differences in the susceptibility to chronic unpredictable stress (CUS) and the effects of fatty acid amide hydrolase (FAAH) inhibitor URB597 in rats have been investigated in this study. In this context, we investigated the effects of prolonged treatment with URB597 on behavior, pro-inflammatory interleukin-6 (IL-6) and anti-inflammatory interleukin-10 (IL-10), catecholamine content and the expression of its biosynthetic and degrading enzymes in the hippocampus, hypothalamus and medial prefrontal cortex (mPFC) of rats subjected to CUS. The results show that CUS increases anxiety-like and depression-like behaviors but it was more pronounced in females. The data suggests sex differences in brain cytokines, catecholamines and their enzymes of synthesis and degradation expression in response to CUS. Our findings indicate that the FAAH inhibitor URB597 differently regulated catecholamine levels and its enzymes of synthesis and degradation in the examined brain areas of male and female rats. URB treatment failed to reduce anxiety or restore reduced norepinephrine and did not affect enzymes of catecholamine degradation in the mPFC, hippocampus and hypothalamus of CUS female rats. These studies are important because they investigate the neurochemical consequences of stress related mood disorders that might lead to the development of sex specific treatments.

Acute stress improves the effectivity of cognitive emotion regulation in men

Emotion regulation is crucial for coping with stressors but in turn can also be influenced by stress. Initial studies provided mixed evidence showing either beneficial or impairing stress effects on cognitive emotion regulation depending on stress timing, sex or the regulatory strategy. Here, we investigated the impact of acute stress on different emotion regulation strategies in men and women. N = 118 healthy participants were subjected to the Trier Social Stress Test or a control condition after which they completed an emotion regulation paradigm, requiring them to regulate their emotions in response to negative pictures using reappraisal or distraction. Cortisol levels were repeatedly measured to quantify changes in HPA axis activity. Affective ratings and pupil dilation served to measure emotion regulation success and the cognitive effort to regulate emotions. Stress reduced arousal and increased valence and success ratings for reappraisal in men, whereas no significant stress effects were found in women. Moreover, stressed men displayed a significant expansion of pupil diameter during reappraisal suggesting enhanced cognitive regulatory engagement, which ultimately may have led to better emotion regulation outcomes. Cortisol secretion positively correlated with subjective reappraisal success in men, suggesting a glucocorticoid-driven mechanism that may promote emotion regulatory performance in the aftermath of stress.

Sex differences in resilience: Experiential factors and their mechanisms

Adverse life events can lead to stable changes in brain structure and function and are considered primary sources of risk for post-traumatic stress disorder, depression and other neuropsychiatric disorders. However, most individuals do not develop these conditions following exposure to traumatic experiences, and research efforts have identified a number of experiential factors associated with an individual's ability to withstand, adapt to and facilitate recovery from adversity. While multiple animal models of stress resilience exist, so that the detailed biological mechanisms can be explored, studies have been disproportionately conducted in male subjects even though the prevalence and presentation of stress-linked disorders differ between sexes. This review focuses on (a) the mechanisms by which experiential factors (behavioral control over a stressor, exercise) reduce the impact of adverse events as studied in males; (b) whether other manipulations (ketamine) that buffer against stress-induced sequelae engage the same circuit features; and (c) whether these processes operate similarly in females. We argue that investigation of experiential factors that produce resistance/resilience rather than vulnerability to adversity will generate a unique set of biological mechanisms that potentially underlie sex differences in mood disorders.

Addiction is driven by excessive goal-directed drug choice under negative affect: translational critique of habit and compulsion theory

Drug addiction may be a goal-directed choice driven by excessive drug value in negative affective states, a habit driven by strong stimulus-response associations, or a compulsion driven by insensitivity to costs imposed on drug seeking. Laboratory animal and human evidence for these three theories is evaluated. Excessive goal theory is supported by dependence severity being associated with greater drug choice/economic demand. Drug choice is demonstrably goal-directed (driven by the expected value of the drug) and can be augmented by stress/negative mood induction and withdrawal-effects amplified in those with psychiatric symptoms and drug use coping motives. Furthermore, psychiatric symptoms confer risk of dependence, and coping motives mediate this risk. Habit theory of addiction has weaker support. Habitual behaviour seen in drug-exposed animals often does not occur in complex decision scenarios, or where responding is rewarded, so habit is unlikely to explain most human addictive behaviour where these conditions apply. Furthermore, most human studies have not found greater propensity to habitual behaviour in drug users or as a function of dependence severity, and the minority that have can be explained by task disengagement producing impaired explicit contingency knowledge. Compulsion theory of addiction also has weak support. The persistence of punished drug seeking in animals is better explained by greater drug value (evinced by the association with economic demand) than by insensitivity to costs. Furthermore, human studies have provided weak evidence that propensity to discount cost imposed on drug seeking is associated with dependence severity. These data suggest that human addiction is primarily driven by excessive goal-directed drug choice under negative affect, and less by habit or compulsion. Addiction is pathological because negative states powerfully increase expected drug value acutely outweighing abstinence goals.

Balancing Between Goal-Directed and Habitual Responding Following Acute Stress

Abstract. Instrumental learning is regulated by two memory systems: a relatively rigid but efficient habit system and a flexible but resource-demanding goal-directed system. Previous work has demonstrated that exposure to acute stress may shift the balance between these systems toward the habitual system. In the current study, we used a 2-day outcome devaluation paradigm with a 75% reward contingency rate and altered food reward categories to replicate and extend our previous findings. Participants learned neutral stimulus–response–reward associations on the first day. On the second day, rewards were devalued by eating to satiety. Subsequently, acute stress was induced in half of the participants using the Maastricht Acute Stress Test, while the other half engaged in a nonstressful control task. Finally, relative goal-directed versus habitual behavior was evaluated in a slips-of-action phase, where more slips-of-action indicate a shift toward the habitual system. Results showed that participants successfully acquired the stimulus–response–reward associations, that devaluation was effective, and that stressed participants displayed significant increases in cortisol and blood pressure. Stress led participants to commit more slips-of-action compared with nonstressed controls. The current study extends previous work, showing that the employed paradigm and outcome devaluation procedure are boundary conditions to the stress-induced shift in instrumental responding.

Cortisol modulates the engagement of multiple memory systems: Exploration of a common NR3C2 polymorphism

Exposure to acute stress has been shown to result in a shift from declarative toward non-declarative learning, presumably mediated by brain mineralocorticoid receptors (MRs). In this study, we aimed to replicate and extend these findings by investigating the role of stress-associated cortisol secretion on learning behavior. Furthermore, we explored the influence of a well-characterized common single nucleotide polymorphism of the MR gene (rs2070951; minor allele frequency: 49.3%) previously shown to influence MR expression and HPA axis activity. Healthy males (n = 74) were exposed to the Trier Social Stress Test or a control condition prior to performing a probabilistic classification task (Weather Prediction Task). The use of a non-declarative learning strategy continuously increased over the course of the learning task after stress exposure, but leveled in the control condition. The shift toward a non-declarative strategy in the stress group was associated with better learning performance. Higher pre-stress cortisol levels favored the adoption of a non-declarative learning strategy. rs2070951 C/C-carriers in contrast to G-allele carriers exhibited a larger secretion of cortisol under stress. Furthermore, control participants homozygous for the C-allele adopted a non-declarative learning strategy less often than stressed participants, whereas the choice of strategy was independent of stress in G-allele carriers. The failure to switch strategies resulted in poorer performance, suggesting a beneficial effect of stress in dependence of MR variation. Consistent with previous findings, the results provide further support for cortisol as a driving force in coordinating the competition between multiple memory systems under stress.

The role of serotonin 1B in the representation of outcomes

Disrupted serotonin neurotransmission has been implicated in the etiology of psychopathic traits. Empirical research has found that people with high levels of psychopathic traits have a deficit in reinforcement learning that is thought to be linked with amygdala dysfunction. Altered serotonin neurotransmission provides a plausible explanation for amygdala dysfunction in psychopathic traits and recent research suggests that this may be associated with serotonin 1B (5-HT_1B) receptor function. This research used an animal model to test the hypothesis that 5-HT_1B receptors are involved in the encoding of the specific features of reinforcing outcomes. An outcome devaluation task was used to test the effect of the systemic administration of a selective 5-HT_1B receptor agonist administered before encoding of “action-outcome” associations. Results showed that while administration of a 5-HT_1B receptor agonist allowed rats to acquire instrumental responding for food, when the content of that learning was further probed using an outcome devaluation task, performance differed from controls. 5-HT_1B agonism impaired learning about the specific sensory qualities of food rewards associated with distinct instrumental responses, required to direct choice performance when the value of one outcome changed. These findings suggest a role for 5-HT_1B receptor function in the encoding of the specific features of reinforcing outcomes.

Stress-induced impairment in goal-directed instrumental behaviour is moderated by baseline working memory

Acute stress has been found to impair goal-directed instrumental behaviour, a cognitively flexible behaviour that requires cognitive control. The current study aimed to investigate the role of individual differences in baseline and stress-induced changes in working memory (WM) on the shift to less goal-directed responding under stress. To this end, 112 healthy participants performed an instrumental learning task. In phase 1, participants learned instrumental actions that were associated with two different food rewards. In phase 2, one of these food rewards was devalued by eating until satiety. Before the extinction test in phase 3, participants were subjected to the Maastricht Acute Stress Test or a no-stress control procedure. Results showed that the effect of stress on instrumental behaviour is modulated by baseline, but not stress-induced changes in WM capacity. Specifically, only at low baseline WM capacity did stress induce a shift to less goal-directed behaviour. These findings highlight that our cognitive resources are limited and for those who already have limited resources at baseline taking into account motivational value is impaired under stress.

Drug-Induced Glucocorticoids and Memory for Substance Use

The biological stress response of the body forms one of the foundations of adaptive behavior, including promoting (and impairing) different forms of memory. This response transcends stressful experiences and underlies reactions to challenges and even reinforcers such as addictive substances. Nevertheless, drug-induced stress responses are rarely incorporated into models of addiction. We propose here that drug-induced stress responses (particularly glucocorticoids) play a crucial role in addictive behavior by modulating the formation of memories for substance-use experiences. We review the contributions of amygdala-, striatum-, and hippocampus-based memory systems to addiction, and reveal common effects of addictive drugs and acute stress on these different memories. We suggest that the contributions of drug-induced stress responses to memory may provide insights into the mechanisms driving addictive behavior.

Stress-induced reliance on habitual behavior is moderated by cortisol reactivity

Instrumental learning, i.e., learning that specific behaviors lead to desired outcomes, occurs through goal-directed and habit memory systems. Exposure to acute stress has been shown to result in less goal-directed control, thus rendering behavior more habitual. The aim of the current studies was to replicate and extend findings on stress-induced prompting of habitual responding and specifically focused on the role of stress-induced cortisol reactivity. Study 1 used an established outcome devaluation paradigm to assess goal-directed and habitual control. Study 2 utilized a modified version of this paradigm that was intended to establish stronger habitual responding through more extensive reward training and applying a relevant behavioral devaluation procedure (i.e., eating to satiety). Both studies failed to replicate that stress overall, i.e., independent of cortisol reactivity, shifted behavior from goal-directed to habitual control. However, both studies found that relative to stress-exposed cortisol non-responders and no-stress controls, participants displaying stress-induced cortisol reactivity displayed prominent habitual responding. These findings highlight the importance of stress-induced cortisol reactivity in facilitating habits.

Behavioural and neural sequelae of stressor exposure are not modulated by controllability in females

The degree of behavioural control that an organism has over a stressor is a potent modulator of the stressor's impact; controllable stressors produce none of the neurochemical and behavioural sequelae that occur if the stressor is uncontrollable. Research demonstrating the importance of control and the neural mechanisms responsible has been conducted almost entirely with male rats. It is unknown if behavioural control is stress blunting in females, and whether or not a similar resilience circuitry is engaged. Female rats were exposed to controllable, yoked uncontrollable or no tailshock. In separate experiments, behavioural (juvenile social exploration, fear and shuttle box escape) and neurochemical (activation of dorsal raphe serotonin and dorsal raphe-projecting prelimbic neurons) outcomes, which are sensitive to the dimension of control in males, were assessed. Despite successful acquisition of the controlling response, behavioural control did not mitigate dorsal raphe serotonergic activation and behavioural outcomes induced by tailshock, as it does in males. Moreover, behavioural control failed to selectively engage prelimbic cells that project to the dorsal raphe as in males. Pharmacological activation of the prelimbic cortex restored the stress-buffering effects of control. Collectively, the data demonstrate stressor controllability phenomena are absent in females and that the protective prelimbic circuitry is present but not engaged. Reduced benefit from coping responses may represent a novel approach for understanding differential sex prevalence in stress-related psychiatric disorders.