Prefrontal cortex mediates extinction of responding by two distinct neural mechanisms in accumbens shell

An open-source behavior controller for associative learning and memory (B-CALM)

Associative learning and memory, i.e., learning and remembering the associations between environmental stimuli, self-generated actions, and outcomes such as rewards or punishments, are critical for the well-being of animals. Hence, the neural mechanisms underlying these processes are extensively studied using behavioral tasks in laboratory animals. Traditionally, these tasks have been controlled using commercial hardware and software, which limits scalability and accessibility due to their cost. More recently, due to the revolution in microcontrollers or microcomputers, several general-purpose and open-source solutions have been advanced for controlling neuroscientific behavioral tasks. While these solutions have great strength due to their flexibility and general-purpose nature, for the same reasons, they suffer from some disadvantages including the need for considerable programming expertise, limited online visualization, or slower than optimal response latencies for any specific task. Here, to mitigate these concerns, we present an open-source behavior controller for associative learning and memory (B-CALM). B-CALM provides an integrated suite that can control a host of associative learning and memory behaviors. As proof of principle for its applicability, we show data from head-fixed mice learning Pavlovian conditioning, operant conditioning, discrimination learning, as well as a timing task and a choice task. These can be run directly from a user-friendly graphical user interface (GUI) written in MATLAB that controls many independently running Arduino Mega microcontrollers in parallel (one per behavior box). In sum, B-CALM will enable researchers to execute a wide variety of associative learning and memory tasks in a scalable, accurate, and user-friendly manner.

Human ventromedial prefrontal cortex lesions enhance the effect of expectations on pain perception

Pain is strongly modulated by expectations and beliefs. Across species, subregions of ventromedial prefrontal cortex (VMPFC) are implicated in a variety of functions germane to pain, predictions, and learning. Human fMRI studies show that VMPFC activity tracks expectations about pain and mediates expectancy effects on pain-related activity in other brain regions. Prior lesion studies suggest that VMPFC may instead play a more general role in generating affective responses to painful stimuli. To test whether VMPFC is required to generate affective responses to pain or is more specifically involved in expectancy-based pain modulation, we studied responses to heat stimuli in five adults with bilateral surgical lesions of VMPFC and twenty healthy adults without brain damage. All participants underwent a quantitative sensory testing procedure followed by a pain expectancy task in which cues predicting either low or high pain were followed by intermittent medium intensity heat stimuli. Compared to adults without brain damage, individuals with VMPFC lesions reported larger differences in expected pain based on predictive cues and failed to update expectations following the covert introduction of unexpected medium temperature stimuli. Consistent with observed expectancy differences, subjective pain unpleasantness ratings in the VMPFC lesion group were more strongly modulated by cue during thermal stimulation. We found no group differences in overall pain sensitivity, nor in relationships between pain and autonomic arousal, suggesting that VMPFC damage specifically enhances the effect of expectations on pain processing, likely driven by impaired integration of new sensory feedback to update expectations about pain. These results provide essential new data regarding the specific functional contribution of VMPFC to pain modulation.

Prelimbic and infralimbic medial prefrontal cortex neuron activity signals cocaine seeking variables across multiple timescales

RATIONALE AND OBJECTIVES

The prefrontal cortex is critical for execution and inhibition of reward seeking. Neural manipulation of rodent medial prefrontal cortex (mPFC) subregions differentially impacts execution and inhibition of cocaine seeking. Dorsal, or prelimbic (PL), and ventral, or infralimbic (IL) mPFC are implicated in cocaine seeking or extinction of cocaine seeking, respectively. This differentiation is not seen across all studies, indicating that further research is needed to understand specific mPFC contributions to drug seeking.

METHODS

We recorded neuronal activity in mPFC subregions during cocaine self-administration, extinction, and cue- and cocaine-induced reinstatement of cocaine seeking.

RESULTS

Both PL and IL neurons were phasically responsive around lever presses during cocaine self-administration, and activity in both areas was reduced during extinction. During both cue- and, to a greater extent, cocaine-induced reinstatement, PL neurons exhibited significantly elevated responses, in line with previous studies demonstrating a role for the region in relapse. The enhanced PL signaling in cocaine-induced reinstatement was driven by strong excitation and inhibition in different groups of neurons. Both of these response types were stronger in PL vs. IL neurons. Finally, we observed tonic changes in activity in all tasks phases, reflecting both session-long contextual modulation as well as minute-to-minute activity changes that were highly correlated with brain cocaine levels and motivation associated with cocaine seeking.

CONCLUSIONS

Although some differences were observed between PL and IL neuron activity across sessions, we found no evidence of a go/stop dichotomy in PL/IL function. Instead, our results demonstrate temporally heterogeneous prefrontal signaling during cocaine seeking and extinction in both PL and IL, revealing novel and complex functions for both regions during these behaviors. This combination of findings argues that mPFC neurons, in both PL and IL, provide multifaceted contributions to the regulation of drug seeking and addiction.

Aberrant impulse control circuitry in obesity

The ventromedial prefrontal cortex (vmPFC) to nucleus accumbens (NAc) circuit has been implicated in impulsive reward-seeking. This disinhibition has been implicated in obesity and often manifests as binge eating, which is associated with worse treatment outcomes and comorbidities. It remains unclear whether the vmPFC-NAc circuit is perturbed in impulsive eaters with obesity. Initially, we analyzed publicly available, high-resolution, normative imaging data to localize where vmPFC structural connections converged within the NAc. These structural connections were found to converge ventromedially in the presumed NAc shell subregion. We then analyzed multimodal clinical and imaging data to test the a priori hypothesis that the vmPFC-NAc shell circuit is linked to obesity in a sample of female participants that regularly engaged in impulsive eating (i.e., binge eating). Functionally, vmPFC-NAc shell resting-state connectivity was inversely related to body mass index (BMI) and decreased in the obese state. Structurally, vmPFC-NAc shell structural connectivity and vmPFC thickness were inversely correlated with BMI; obese binge-prone participants exhibited decreased vmPFC-NAc structural connectivity and vmPFC thickness. Finally, to examine a causal link to binge eating, we directly probed this circuit in one binge-prone obese female using NAc deep brain stimulation in a first-in-human trial. Direct stimulation of the NAc shell subregion guided by local behaviorally relevant electrophysiology was associated with a decrease in number of weekly episodes of uncontrolled eating and decreased BMI. This study unraveled vmPFC-NAc shell circuit aberrations in obesity that can be modulated to restore control over eating behavior in obesity.

A systematic review of neural, cognitive, and clinical studies of anger and aggression

Anger and aggression have large impact on people's safety and the society at large. In order to provide an intervention to minimise aggressive behaviours, it is important to understand the neural and cognitive aspects of anger and aggression. In this systematic review, we investigate the cognitive and neural aspects of anger-related processes, including anger-related behaviours and anger reduction. Using this information, we then review prior existing methods on the treatment of anger-related disorders as well as anger management, including mindfulness and cognitive behavioural therapy. At the cognitive level, our review that anger is associated with excessive attention to anger-related stimuli and impulsivity. At the neural level, anger is associated with abnormal functioning of the amygdala and ventromedial prefrontal cortex. In conclusions, based on cognitive and neural studies, we here argue that mindfulness based cognitive behavioural therapy may be better at reducing anger and aggression than other behavioural treatments, such as cognitive behavioural therapy or mindfulness alone. We provide key information on future research work and best ways to manage anger and reduce aggression. Importantly, future research should investigate how anger related behaviours is acquired and how stress impacts the development of anger.

Cortico-Striatal Control over Adaptive Goal-Directed Responding Elicited by Cues Signaling Sucrose Reward or Punishment

The medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) have been associated with the expression of adaptive and maladaptive behavior elicited by fear-related and drug-associated cues. However, reported effects of mPFC manipulations on cue-elicited natural reward-seeking and inhibition thereof have been varied, with few studies examining cortico-striatal contributions in tasks that require adaptive responding to cues signaling reward and punishment within the same session. The current study aimed to better elucidate the role of mPFC and NAc subdivisions, and their functional connectivity in cue-elicited adaptive responding using a novel discriminative cue responding task. Male Long-Evans rats learned to lever-press on a VR5 schedule for a discriminative cue signaling reward, and to avoid pressing the same lever in the presence of another cue signaling punishment. Postacquisition, prelimbic (PL) and infralimbic (IL) areas of the mPFC, NAc core, shell, PL-core, or IL-shell circuits were pharmacologically or chemogenetically inhibited while animals performed under (1) nonreinforced (extinction) conditions, where the appetitive and aversive cues were presented in alternating trials alone or as a compound stimulus; and (2) reinforced conditions, whereby cued responding was accompanied by associated outcomes. PL and IL inactivation attenuated nonreinforced and reinforced goal-directed cue responding, whereas NAc core and shell inactivation impaired nonreinforced responding for the appetitive, but not aversive cue. Furthermore, PL-core and IL-shell inhibition disinhibited nonreinforced but not reinforced cue responding. Our findings implicate the mPFC as a site of confluence of motivationally significant cues and outcomes, and in the regulation of nonreinforced cue responding via downstream NAc targets.SIGNIFICANCE STATEMENT The ability to discriminate and respond appropriately to environmental cues that signal availability of reward or punishment is essential for survival. The medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) have been implicated in adaptive and maladaptive behavior elicited by fear-related and drug-associated cues. However, less is known about the role they play in orchestrating adaptive responses to natural reward and punishment cues within the same behavioral task. Here, using a novel discriminative cue responding task combined with pharmacological or chemogenetic inhibition of mPFC, NAc and mPFC-NAc circuits, we report that mPFC is critically involved in responding to changing cued response-outcomes, both when the responses are reinforced, and nonreinforced. Furthermore, the mPFC coordinates nonreinforced discriminative cue responding by suppressing inappropriate responding via downstream NAc targets.

The rodent medial prefrontal cortex and associated circuits in orchestrating adaptive behavior under variable demands

Emerging evidence implicates rodent medial prefrontal cortex (mPFC) in tasks requiring adaptation of behavior to changing information from external and internal sources. However, the computations within mPFC and subsequent outputs that determine behavior are incompletely understood. We review the involvement of mPFC subregions, and their projections to the striatum and amygdala in two broad types of tasks in rodents: 1) appetitive and aversive Pavlovian and operant conditioning tasks that engage mPFC-striatum and mPFC-amygdala circuits, and 2) foraging-based tasks that require decision making to optimize reward. We find support for region-specific function of the mPFC, with dorsal mPFC and its projections to the dorsomedial striatum supporting action control with higher cognitive demands, and ventral mPFC engagement in translating affective signals into behavior via discrete projections to the ventral striatum and amygdala. However, we also propose that defined mPFC subdivisions operate as a functional continuum rather than segregated functional units, with crosstalk that allows distinct subregion-specific inputs (e.g., internal, affective) to influence adaptive behavior supported by other subregions.

Local accumbens in vivo imaging during deep brain stimulation reveals a strategy-dependent amelioration of hedonic feeding

Impulsive overeating is a common, disabling feature of eating disorders. Calcium imaging using fiber photometry has emerged as an in vivo methodology to measure neuronal population activity immune to electrical stimulation artifact from deep brain stimulation (DBS). Thus, when used simultaneously, calcium imaging can elucidate poorly understood DBS mechanisms. We show that nucleus accumbens D1 medial spiny calcium signaling increases in preparation of hedonic feeding of high-fat food. Further, responsive, over continuous, DBS strategies effectively disrupt this activity leading to decreased consumption. Implementation of this methodology to better understand mechanisms of these and other forms of neuromodulation for various indications may help advance the field to identify novel therapeutic targets with applications extending beyond obesity.

Impulsive overeating is a common, disabling feature of eating disorders. Both continuous deep brain stimulation (DBS) and responsive DBS, which limits current delivery to pathological brain states, have emerged as potential therapies. We used in vivo fiber photometry in wild-type, Drd1-cre, and A2a-cre mice to 1) assay subtype-specific medium spiny neuron (MSN) activity of the nucleus accumbens (NAc) during hedonic feeding of high-fat food, and 2) examine DBS strategy-specific effects on NAc activity. D1, but not D2, NAc GCaMP activity increased immediately prior to high-fat food approach. Responsive DBS triggered a GCaMP surge throughout the stimulation period and durably reduced high-fat intake. However, with continuous DBS, this surge decayed, and high-fat intake reemerged. Our results argue for a stimulation strategy-dependent modulation of D1 MSNs with a more sustained decrease in consumption with responsive DBS. This study illustrates the important role in vivo imaging can play in understanding effects of such novel therapies.

Prefrontal-hippocampal interactions supporting the extinction of emotional memories: the retrieval stopping model

Neuroimaging has revealed robust interactions between the prefrontal cortex and the hippocampus when people stop memory retrieval. Efforts to stop retrieval can arise when people encounter reminders to unpleasant thoughts they prefer not to think about. Retrieval stopping suppresses hippocampal and amygdala activity, especially when cues elicit aversive memory intrusions, via a broad inhibitory control capacity enabling prepotent response suppression. Repeated retrieval stopping reduces intrusions of unpleasant memories and diminishes their affective tone, outcomes resembling those achieved by the extinction of conditioned emotional responses. Despite this resemblance, the role of inhibitory fronto-hippocampal interactions and retrieval stopping broadly in extinction has received little attention. Here we integrate human and animal research on extinction and retrieval stopping. We argue that reconceptualising extinction to integrate mnemonic inhibitory control with learning would yield a greater understanding of extinction's relevance to mental health. We hypothesize that fear extinction spontaneously engages retrieval stopping across species, and that controlled suppression of hippocampal and amygdala activity by the prefrontal cortex reduces fearful thoughts. Moreover, we argue that retrieval stopping recruits extinction circuitry to achieve affect regulation, linking extinction to how humans cope with intrusive thoughts. We discuss novel hypotheses derived from this theoretical synthesis.

The learning of prospective and retrospective cognitive maps within neural circuits

Brain circuits are thought to form a "cognitive map" to process and store statistical relationships in the environment. A cognitive map is commonly defined as a mental representation that describes environmental states (i.e., variables or events) and the relationship between these states. This process is commonly conceptualized as a prospective process, as it is based on the relationships between states in chronological order (e.g., does reward follow a given state?). In this perspective, we expand this concept on the basis of recent findings to postulate that in addition to a prospective map, the brain forms and uses a retrospective cognitive map (e.g., does a given state precede reward?). In doing so, we demonstrate that many neural signals and behaviors (e.g., habits) that seem inflexible and non-cognitive can result from retrospective cognitive maps. Together, we present a significant conceptual reframing of the neurobiological study of associative learning, memory, and decision making.

Neural Responsivity to Reward versus Punishment Shortly after Trauma Predicts Long-term Development of Post-Traumatic Stress Symptoms

BACKGROUND

Processing negative and positive valenced stimuli involve multiple brain regions including the amygdala and ventral striatum (VS). Post-Traumatic Stress Disorder (PTSD) is often associated with hyper-responsivity to negatively valenced, yet recent evidence also points to deficient positive valence functioning. It is yet unclear what is the relative contribution of such opposing valence processing shortly after trauma to the development of chronic PTSD.

METHODS

Neurobehavioral indicators of motivational positive vs. negative valence sensitivities were longitudinally assessed in 171 adults (87 females, age=34.19±11.47 years) at 1-, 6-, and 14-months following trauma exposure (TP1, TP2, TP3). Using a gambling fMRI paradigm, amygdala and VS functionality (activity and functional connectivity with the prefrontal cortex) in response to rewards vs. punishments were assessed with relation to PTSD severity at different time-points. The effect of valence processing was depicted behaviorally by the amount of risk taken to maximize reward.

RESULTS

PTSD severity at TP1 was associated with greater neural functionality in the amygdala (but not the VS) towards punishments vs. rewards, and fewer risky choices. PTSD severity at TP3 was associated with decreased neural functionality in both the VS and amygdala towards rewards vs. punishments at TP1 (but not with risky behavior). Explainable machine learning revealed the primacy of VS biased processing, over the amygdala, in predicting PTSD severity at TP3.

CONCLUSIONS

These results highlight the importance of biased neural responsivity to positive relative to negative motivational outcomes in PTSD development. Novel therapeutic strategies early after trauma may thus target both valence fronts.

Emergence of complex dynamics of choice due to repeated exposures to extinction learning

Extinction learning, the process of ceasing an acquired behavior in response to altered reinforcement contingencies, is not only essential for survival in a changing environment, but also plays a fundamental role in the treatment of pathological behaviors. During therapy and other forms of training involving extinction, subjects are typically exposed to several sessions with a similar structure. The effects of this repeated exposure are not well understood. Here, we studied the behavior of pigeons across several sessions of a discrimination-learning task in context A, extinction in context B, and a return to context A to test the context-dependent return of the learned responses (ABA renewal). By focusing on individual learning curves across animals, we uncovered a session-dependent variability of behavior: (1) during extinction, pigeons preferred the unrewarded alternative choice in one-third of the sessions, predominantly during the first one. (2) In later sessions, abrupt transitions of behavior at the onset of context B emerged, and (3) the renewal effect decayed as sessions progressed. We show that the observed results can be parsimoniously accounted for by a computational model based only on associative learning between stimuli and actions. Our work thus demonstrates the critical importance of studying the trial-by-trial dynamics of learning in individual sessions, and the power of “simple” associative learning processes.

Nucleus accumbens fast-spiking interneurons in motivational and addictive behaviors

The development of drug addiction is associated with functional adaptations within the reward circuitry, within which the nucleus accumbens (NAc) is anatomically positioned as an interface between motivational salience and behavioral output. The functional output of NAc is profoundly altered after exposure to drugs of abuse, and some of the functional changes continue to evolve during drug abstinence, contributing to numerous emotional and motivational alterations related drug taking, seeking, and relapse. As in most brain regions, the functional output of NAc is critically dependent on the dynamic interaction between excitation and inhibition. One of the most prominent sources of inhibition within the NAc arises from fast-spiking interneurons (FSIs). Each NAc FSI innervates hundreds of principal neurons, and orchestrates population activity through its powerful and sustained feedforward inhibition. While the role of NAc FSIs in the context of drug addiction remains poorly understood, emerging evidence suggests that FSIs and FSI-mediated local circuits are key targets for drugs of abuse to tilt the functional output of NAc toward a motivational state favoring drug seeking and relapse. In this review, we discuss recent findings and our conceptualization about NAc FSI-mediated regulation of motivated and cocaine-induced behaviors. We hope that the conceptual framework proposed in this review may provide a useful guidance for ongoing and future studies to determine how FSIs influence the function of NAc and related reward circuits, ultimately leading to addictive behaviors.

Prefrontal cortical and nucleus accumbens contributions to discriminative conditioned suppression of reward-seeking

Fear can potently inhibit ongoing behavior, including reward-seeking, yet the neural circuits that underlie such suppression remain to be clarified. Prior studies have demonstrated that distinct subregions of the rodent medial prefrontal cortex (mPFC) differentially affect fear behavior, whereby fear expression is promoted by the more dorsal prelimbic cortex (PL) and inhibited by the more ventral infralimbic cortex (IL). These mPFC regions project to subregions of the nucleus accumbens, the core (NAcC) and shell (NAcS), that differentially contribute to reward-seeking as well as affective processes that may be relevant to fear expression. Here, we investigated how these mPFC and NAc subregions contribute to discriminative fear conditioning, assessed by conditioned suppression of reward-seeking. Bilateral inactivation of the NAcS or PL reduced the expression of conditioned suppression to a shock-associated CS+, whereas NAcC inactivation reduced reward-seeking without affecting suppression. IL inactivation caused a general reduction in conditioned suppression following discriminative conditioning, but not when using a single-stimulus design. Pharmacological disconnection of the PL → NAcS pathway revealed that this projection mediates conditioned suppression. These data add to a growing literature implicating discrete cortico-striatal pathways in the suppression of reward-seeking in response to aversive stimuli. Dysfunction within related structures may contribute to aberrant patterns of behavior in psychiatric illnesses including substance use disorders.

Prefrontal Regulation of Punished Ethanol Self-administration

BACKGROUND

A clinical hallmark of alcohol use disorder is persistent drinking despite potential adverse consequences. The ventromedial prefrontal cortex (vmPFC) and dorsomedial prefrontal cortex (dmPFC) are positioned to exert top-down control over subcortical regions, such as the nucleus accumbens shell (NAcS) and basolateral amygdala, which encode positive and negative valence of ethanol (EtOH)-related stimuli. Prior rodent studies have implicated these regions in regulation of punished EtOH self-administration (EtOH-SA).

METHODS

We conducted in vivo electrophysiological recordings in mouse vmPFC and dmPFC to obtain neuronal correlates of footshock-punished EtOH-SA. Ex vivo recordings were performed in NAcS D₁ receptor-expressing medium spiny neurons receiving vmPFC input to examine punishment-related plasticity in this pathway. Optogenetic photosilencing was employed to assess the functional contribution of the vmPFC, dmPFC, vmPFC projections to NAcS, or vmPFC projections to basolateral amygdala, to punished EtOH-SA.

RESULTS

Punishment reduced EtOH lever pressing and elicited aborted presses (lever approach followed by rapid retraction). Neurons in the vmPFC and dmPFC exhibited phasic firing to EtOH lever presses and aborts, but only in the vmPFC was there a population-level shift in coding from lever presses to aborts with punishment. Closed-loop vmPFC, but not dmPFC, photosilencing on a postpunishment probe test negated the reduction in EtOH lever presses but not in aborts. Punishment was associated with altered plasticity at vmPFC inputs to D₁ receptor-expressing medium spiny neurons in the NAcS. Photosilencing vmPFC projections to the NAcS, but not to the basolateral amygdala, partially reversed suppression of EtOH lever presses on probe testing.

CONCLUSIONS

These findings demonstrate a key role for the vmPFC in regulating EtOH-SA after punishment, with implications for understanding the neural basis of compulsive drinking in alcohol use disorder.

Prelimbic and Infralimbic Prefrontal Regulation of Active and Inhibitory Avoidance and Reward-Seeking

Flexible initiation or suppression of actions to avoid aversive events is crucial for survival. The prelimbic (PL) and infralimbic (IL) regions of the medial prefrontal cortex (mPFC) have been implicated in different aspects of avoidance and reward-seeking, but their respective contribution in instigating versus suppressing actions in aversive contexts remains to be clarified. We examined mPFC involvement in different forms of avoidance in rats well trained on different cued lever-press avoidance tasks. Active/inhibitory avoidance required flexible discrimination between auditory cues signaling foot-shock could be avoided by making or withholding instrumental responses. On a simpler active avoidance task, a single cue signaled when a lever press would avoid shock. PL inactivation disrupted active but not inhibitory avoidance on the discriminative task while having no effect on single-cued avoidance. In comparison, IL inactivation broadly impaired active and inhibitory avoidance. Conversely, on a cued appetitive go/no-go task, both IL and PL inactivation impaired inhibitory but not active reward-seeking, the latter effect being diametrically opposite to that observed on the avoidance task. These findings highlight the complex manner in which different mPFC regions aid in initiating or inhibiting actions in the service of avoiding aversive outcomes or obtaining rewarding ones. IL facilitates active avoidance but suppress inappropriate actions in appetitive and aversive contexts. In contrast, contextual valence plays a critical role in how the PL is recruited in initiating or suppressing actions, which may relate to the degree of cognitive control required to flexibly negotiate response or motivational conflicts and override prepotent behaviors.SIGNIFICANCE STATEMENT Choosing to make or withhold actions in a context-appropriate manner to avoid aversive events or obtain other goals is a critical survival skill. Different medial prefrontal cortex (mPFC) regions have been implicated in certain aspects of avoidance, but their contributions to instigating or suppressing actions remains to be clarified. Here, we show that the dorsal, prelimbic (PL) region of the medial PFC aids active avoidance in situations requiring flexible mitigation of response conflicts, but also aids in withholding responses to obtain rewards. In comparison the ventral infralimbic (IL) cortex plays a broader role in active and inhibitory avoidance as well as suppressing actions to obtain rewards. These findings provide insight into mechanisms underlying normal and maladaptive avoidance behaviors and response inhibition.

Dissociable roles for the ventral and dorsal medial prefrontal cortex in cue-guided risk/reward decision making

Converging evidence from studies with animals and humans have implicated separate regions of the medial prefrontal cortex (mPFC) corresponding to the anterior cingulate cortex (ACC), in mediating different aspects of reward-related decisions involving uncertainty or risk. However, the dissociable contributions of subregions of the ACC remain unclear, as discrepancies exist between human neuroimaging findings and preclinical rodent studies. To clarify how ventral vs. dorsal regions of the mPFC contribute to risk/reward decision making, the present study assessed the effects of inactivation of different subregions on performance of a "Blackjack task" that measured cue-guided decision making and shares similarities with paradigms used with humans. Male, Long-Evans rats were well-trained to choose between a Small/Certain reward vs a Large/Risky reward delivered with variable probabilities (i.e., good vs. poor-odds, 50% vs. 12.5%). The odds of obtaining the larger reward was signaled by auditory cues at the start of each trial. Inactivation of the ventral, infralimbic region of the mPFC increased risky choice selectively when the odds of winning were poor. By contrast, inactivation of the prelimbic and anterior cingulate regions of the dorsal mPFC led to suboptimal reductions in risky choice on good-odds trials. The effects of prelimbic vs anterior cingulate inactivations were associated with context-dependent alterations in reward vs negative feedback, respectively. These results further clarify the distinct yet complementary manners in which separate ACC regions promote optimal risk/reward decision making and complement neuroimaging findings that activity in human ventral vs dorsal ACC promotes risk aversion or risky choices.

Women at Greater Sexual Risk for STIs/HIV Have a Lower Mesolimbic and Affective Bias Response to Sexual Stimuli

Young adult women in the United States have high rates of sexually transmitted infections, increasing the risk of human immunodeficiency virus (HIV). The underlying neurobiology of behaviors that increase the probability of contracting sexually-transmitted diseases (STIs) and HIV is just beginning to be explored. The current study assessed the link between sexual risk and the brain and behavioral response to sexual cues in emerging adult women. Our hypothesis was that women with more activity in reward/motivational circuitry would report higher sexual risk behaviors and would evidence higher positive affective bias to visual sexual stimuli. Women (n = 52; age = 18–24 years) who had protected sex 100% of the time (n = 17) vs. those who did not (n = 35), in the past 3 months, were compared on their brain response to 500 ms evocative (sex, aversive, food) vs. neutral cues in a blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) fast event-related design. Based on existing literature, an a priori anatomical “cue-reactive” mask was used to constrain the analyses. Self-reported sexual activity and the affective bias scores to sexual cues were examined as correlates with the brain response to cues. In contrast to our initial hypothesis, the higher sexual risk (Unprotected) group had significantly less activation in mesolimbic brain regions and lower (less positive) affective bias scores to sexual cues compared to the lower risk (Protected) group. As predicted, the brain response was positively correlated with sexual bias. Follow-up analyses showed an effect of partner “risk” (e.g., more vs. less knowledge of partner’s STIs/HIV status). This evidence suggests that women who have protected sex may view sexual-related stimuli more positively, reflected by a neural response in reward/motivational regions and more positive sexual bias scores. In contrast, young women at increased risk for STIs/HIV may feel more negatively about sexual-related stimuli, evidenced by a lower mesolimbic response and a less positive affective bias to sexual cues. These data may help identify young women who are at greatest risk for acquiring STIs and/or HIV, which carries added importance with the availability of new medications that can prevent HIV.

Targeting the Neuronal Activity of Prefrontal Cortex: New Directions for the Therapy of Depression

Depression is one of the prevalent psychiatric illnesses with a comprehensive performance such as low self-esteem, lack of motivation, anhedonia, poor appetite, low energy, and uncomfortableness without a specific cause. So far, the cause of depression is not very clear, but it is certain that many aspects of biological psychological and social environment are involved in the pathogenesis of depression. Recently, the prefrontal cortex (PFC) has been indicated to be a pivotal brain region in the pathogenesis of depression. And increasing evidence showed that the abnormal activity of the PFC neurons is linked with depressive symptoms. Unveiling the molecular and cellular, as well as the circuit properties of the PFC neurons will help to find out how abnormalities in PFC neuronal activity are associated with depressive disorders. In addition, concerning many antidepressant drugs, in this review, we concluded the effect of several antidepressants on PFC neuronal activity to better understand its association with depression.

The Nucleus Accumbens Core Is Necessary for Responding to Incentive But Not Instructive Stimuli

An abundant literature has highlighted the importance of the nucleus accumbens core (NAcC) in behavioral tasks dependent on external stimuli. Yet, some studies have also reported the absence of involvement of the NAcC in stimuli processing. We aimed at comparing, in male rats, the underlying neuronal determinants of incentive and instructive stimuli in the same task. We developed a variant of a GO/NOGO task that reveals important differences in these two types of stimuli. The incentive stimulus invites the rat to engage in the task sequence. Once the rat has decided to initiate a trial, it remains engaged in the task until the end of the trial. This task revealed the differential contribution of the NAcC to responding to different types of stimuli: responding to the incentive stimulus depended on NAcC AMPA/NMDA and dopamine D1 receptors, but the retrieval of the response associated with the instructive stimuli (lever pressing on GO, withholding on NOGO) did not. Our electrophysiological study showed that more NAcC neurons responded more strongly to the incentive than the instructive stimuli. Furthermore, when animals did not respond to the incentive stimulus, the induced excitation was suppressed for most projection neurons, whereas interneurons were strongly activated at a latency preceding that found in projection neurons. This work provides insight on the underlying neuronal processes explaining the preferential implication of the NAcC in deciding whether and when to engage in reward-seeking rather than to decide which action to perform.SIGNIFICANCE STATEMENT The nucleus accumbens core (NAcC) is essential to process information carried by reward-predicting stimuli. Yet, stimuli have distinct properties: incentive stimuli orient the attention toward reward-seeking, whereas instructive stimuli inform about the action to perform. Our study shows that, in male rats, NAcC perturbation with glutamate or dopamine antagonists impeded responses to the incentive but not to the instructive stimulus. NAcC neuronal recordings revealed a stronger representation of incentive than instructive stimuli. Furthermore, we found that interneurons are recruited when rats fail to respond to incentive stimuli. This work provides insight on the underlying neuronal processes explaining the preferential implication of the NAcC in deciding whether and when to engage in reward-seeking rather than to decide which action to perform.

Ventromedial prefrontal cortex contributes to performance success by controlling reward-driven arousal representation in amygdala

When preparing for a challenging task, potential rewards can cause physiological arousal that may impair performance. In this case, it is important to control reward-driven arousal while preparing for task execution. We recently examined neural representations of physiological arousal and potential reward magnitude during preparation, and found that performance failure was explained by relatively increased reward representation in the left caudate nucleus and arousal representation in the right amygdala (Watanabe, et al., 2019). Here we examine how prefrontal cortex influences the amygdala and caudate to control reward-driven arousal. Ventromedial prefrontal cortex (VMPFC) exhibited activity that was negatively correlated with trial-wise physiological arousal change, which identified this region as a potential modulator of amygdala and caudate. Next we tested the VMPFC - amygdala - caudate effective network using dynamic causal modeling (Friston et al., 2003). Post-hoc Bayesian model selection (Friston and Penny, 2011) identified a model that best fit data, in which amygdala activation was suppressively controlled by the VMPFC only in success trials. Furthermore, fixed connectivity strength from VMPFC to amygdala explained individual task performance. These findings highlight the role of effective connectivity from VMPFC to amygdala in order to control arousal during preparation for successful performance.

Recruitment and disruption of ventral pallidal cue encoding during alcohol seeking

A critical area of inquiry in the neurobiology of alcohol abuse is the mechanism by which cues gain the ability to elicit alcohol use. Previously, we found that cue-evoked activity in rat ventral pallidum robustly encodes the value of sucrose cues trained under both Pavlovian and instrumental contingencies, despite a stronger relationship between cue-evoked activity and behavioral latency after instrumental training (Richard et al., 2018, Elife, 7, e33107). Here, we assessed: (a) ventral pallidal representations of Pavlovian versus instrumental cues trained with alcohol reward, and (b) the impact of non-associative alcohol exposure on ventral pallidal representations of sucrose cues. Decoding of cue identity based on ventral pallidum firing was blunted for the Pavlovian alcohol cue in comparison to both the instrumental cue trained with alcohol and either cue type trained with sucrose. Further, non-associative alcohol exposure had opposing effects on ventral pallidal encoding of sucrose cues trained on instrumental versus Pavlovian associations, enhancing decoding accuracy for an instrumental discriminative stimulus and reducing decoding accuracy for a Pavlovian conditioned stimulus. These findings suggest that alcohol exposure can drive biased engagement of specific reward-related signals in the ventral pallidum.

Impaired instrumental reversal learning is associated with increased medial prefrontal cortex activity in Sapap3 knockout mouse model of compulsive behavior

Convergent functional neuroimaging findings implicate hyperactivity across the prefrontal cortex (PFC) and striatum in the neuropathology of obsessive compulsive disorder (OCD). The impact of cortico-striatal circuit hyperactivity on executive functions subserved by these circuits is unclear, because impaired recruitment of PFC has also been observed in OCD patients during paradigms assessing cognitive flexibility. To investigate the relationship between cortico-striatal circuit disturbances and cognitive functioning relevant to OCD, Sapap3 knockout mice (KOs) and littermate controls were tested in an instrumental reversal-learning paradigm to assess cognitive flexibility. Cortical and striatal activation associated with reversal learning was assessed via quantitative analysis of expression of the immediate early gene cFos and generalized linear mixed-effects models. Sapap3-KOs displayed heterogeneous reversal-learning performance, with almost half (n = 13/28) failing to acquire the reversed contingency, while the other 15/28 had similar acquisition as controls. Notably, reversal impairments were not correlated with compulsive grooming severity. cFos analysis revealed that reversal performance declined as medial PFC (mPFC) activity increased in Sapap3-KOs. No such relationship was observed in controls. Our studies are among the first to describe cognitive impairments in a transgenic OCD-relevant model, and demonstrate pronounced heterogeneity among Sapap3-KOs. These findings suggest that increased neural activity in mPFC is associated with impaired reversal learning in Sapap3-KOs, providing a likely neural basis for this observed heterogeneity. The Sapap3-KO model is thus a useful tool for future mechanistic studies to determine how mPFC hyperactivity contributes to OCD-relevant cognitive dysfunction.

Role of oxytocin in parental behaviour

Both animal and human studies have provided conclusive evidence that oxytocin (OXT) acts in the brain (eg, medial preoptic area, ventral tegmental area, nucleus accumbens) to promote parental behaviour under different reproductive and physiological conditions. OXT appears to accelerate and strengthen the neural process that makes newborns attractive or rewarding. Furthermore, OXT reduces stress/anxiety and might improve mood and well being, resulting in indirect benefits for parents. However, OXT also plays a role in the development of species reproductive and social strategies, making some species or individuals more prone to display caring activities in nonreproductive contexts. There are important differences in the development of the OXT system and its regulation by gonadal hormones that can make individuals or species very different. Those intra- and interspecific differences in the OXT system have been associated with differences in parental behaviour. For example, differences in OXT levels in body fluids and genetic variants for the OXT and OXT receptor genes have been associated with variability in parental mood and behaviour in humans. Thus, OXT has received much attention as a potential therapeutic agent for affective, emotional and behavioural problems. Despite many preliminary studies indicating promising findings, several unknown aspects of the OXT system remain to be addressed before we can achieve a complete understanding of its function in the brain. The enormous interest that this area of study has attracted in the last decade will likely continually contribute to advancing our understanding of the role of OXT in parental behaviour and other behavioural and physiological functions.

The Multifaceted Role of the Ventromedial Prefrontal Cortex in Emotion, Decision Making, Social Cognition, and Psychopathology

The ventromedial prefrontal cortex (vmPFC) has been implicated in a variety of social, cognitive, and affective functions that are commonly disrupted in mental illness. In this review, we summarize data from a diverse array of human and animal studies demonstrating that the vmPFC is a key node of cortical and subcortical networks that subserve at least three broad domains of psychological function linked to psychopathology. One track of research indicates that the vmPFC is critical for the representation of reward- and value-based decision making, through interactions with the ventral striatum and amygdala. A second track of research demonstrates that the vmPFC is critical for the generation and regulation of negative emotion, through its interactions with the amygdala, bed nucleus of the stria terminalis, periaqueductal gray, hippocampus, and dorsal anterior cingulate cortex. A third track of research shows the importance of the vmPFC in multiple aspects of social cognition, such as facial emotion recognition, theory-of-mind ability, and processing self-relevant information, through its interactions with the posterior cingulate cortex, precuneus, dorsomedial PFC, and amygdala. We then present meta-analytic data revealing distinct subregions within the vmPFC that correspond to each of these three functions, as well as the associations between these subregions and specific psychiatric disorders (depression, posttraumatic stress disorder, addiction, social anxiety disorder, bipolar disorder, schizophrenia, and attention-deficit/hyperactivity disorder). We conclude by describing several translational possibilities for clinical studies of vmPFC-based circuits, including neuropsychological assessment of transdiagnostic functions, anatomical targets for intervention, predictors of treatment response, markers of treatment efficacy, and subtyping within disorders.

Ventral pallidal encoding of reward-seeking behavior depends on the underlying associative structure

Despite its being historically conceptualized as a motor expression site, emerging evidence suggests the ventral pallidum (VP) plays a more active role in integrating information to generate motivation. Here, we investigated whether rat VP cue responses would encode and contribute similarly to the vigor of reward-seeking behaviors trained under Pavlovian versus instrumental contingencies, when these behavioral responses consist of superficially similar locomotor response patterns but may reflect distinct underlying decision-making processes. We find that cue-elicited activity in many VP neurons predicts the latency of instrumental reward seeking, but not of Pavlovian response latency. Further, disruption of VP signaling increases the latency of instrumental but not Pavlovian reward seeking. This suggests that VP encoding of and contributions to response vigor are specific to the ability of incentive cues to invigorate reward-seeking behaviors upon which reward delivery is contingent.

Sounds or other cues associated with receiving a reward can have a powerful effect on an individual’s behavior or emotions. For example, the sound of an ice cream truck might cause salivation and motivate an individual to stand in a long line. Cues may prompt specific actions necessary to receive a reward, for example, approaching the ice cream truck and paying to get an ice cream. This is called instrumental conditioning. Some cues predict reward delivery, without requiring a specific action. This is called Pavlovian conditioning. Pavlovian cues can still prompt actions, such as approaching the truck, even though the action is not required. But exactly what happens in the brain to generate these actions during the two types of learning, is unclear.

Learning more about these reward-driven brain mechanisms might help scientists to develop better treatments for people with addiction or other conditions that involve compulsive reward-seeking behavior. Currently, scientists do not know enough about how the brain triggers this kind of behavior or how these processes lead to relapse in individuals who have been abstinent. Basic studies on the brain mechanisms that trigger reward-seeking behavior are needed.

Now, Richard et al. show that a greater activity in neurons, or brain cells, in a part of the brain called the ventral pallidum predicts a faster response to a reward cue. In the experiments, some rats were trained to approach a certain location when they heard a particular sound in order to receive sugar water, a form of instrumental conditioning. Another group of rats underwent Pavlovian training and learned to expect sugar water every time they heard sound even if they did nothing. Both groups learned to approach the sugar water location when they heard the cue, despite the different training requirements.

Richard et al. measured the activity of neurons in the ventral pallidum when the rats in the two groups heard the reward-associated sound. The experiments showed that the amount of activity in the brain cells in this area predicted whether a rat would approach the sugar-water delivery area and how quickly they would approach the reward after hearing the cue. The predictions were most reliable for rats that had to do something to get the sugar water. When Richard et al. reduced the activity in these cells they found the rats took longer to approach the reward source, but only when this action was required to receive sugar water. The experiments show that the ventral pallidum may provide the motivation to undertake reward-seeking behavior.

Neural correlates of subjective CS/UCS association in appetitive conditioning

Explicit knowledge of conditioned stimulus (CS)/unconditioned stimulus (UCS) associations is proposed as important factor in classical conditioning. However, while previous studies have focused on its roles in fear conditioning, it has been neglected in the context of appetitive conditioning. The present functional magnetic resonance study aimed to investigate neural activation and functional connectivity linked to subjective CS/UCS association in appetitive conditioning. In total, 85 subjects participated in an appetitive acquisition procedure in which a neutral stimulus (CS+) was paired with a monetary reward, while another neutral stimulus (CS-) was never paired with the reward. Directly afterwards, subjective CS/UCS association was assessed by measuring the extent to which the CS+ was thought to be associated with the UCS compared to the CS-. Close relationships were established between subjective CS/UCS association and activations in the primary visual cortex (V1) during the early phase of conditioning and in the striatum during the late conditioning phase. In addition, we observed inverse relationships between subjective CS/UCS association and both V1/ventromedial prefrontal cortex (vmPFC) and striatal/vmPFC connectivity. The results suggest the involvement of decoupling vmPFC connectivity in reward learning in general and the roles of attentional processes in the formation of the subjective CS/UCS association during the early phase and reward prediction during the late phase of appetitive conditioning.

Prefrontal Cortical Opioids and Dysregulated Motivation: A Network Hypothesis

Loss of inhibitory control over appetitively motivated behavior occurs in multiple psychiatric disorders, including drug abuse, behavioral addictions, and eating disorders with binge features. In this opinion article, novel actions of μ-opioid peptides in the prefrontal cortex (PFC) that could contribute to inhibitory control deficits will be discussed. Evidence has accrued to suggest that excessive intra-PFC μ-opioid receptor (μ-OR) signaling alters the PFC response to excitatory drive, resulting in supernormal and incoherent recruitment of multiple PFC output pathways. Affected pathways include functionally opposed PFC→hypothalamus 'appetitive driver' and PFC→striatum 'appetitive limiter' projections. This network perturbation engenders disorganized, impulsive appetitive responses. Evidence supporting this hypothesis from human imaging and animal studies will be discussed, and combinatorial drug treatments targeting μ-ORs and specific PFC subcortical targets will be explored.

Ventromedial Prefrontal Cortex Damage Is Associated with Decreased Ventral Striatum Volume and Response to Reward

The ventral striatum and ventromedial prefrontal cortex (vmPFC) are two central nodes of the "reward circuit" of the brain. Human neuroimaging studies have demonstrated coincident activation and functional connectivity between these brain regions, and animal studies have demonstrated that the vmPFC modulates ventral striatum activity. However, there have been no comparable data in humans to address whether the vmPFC may be critical for the reward-related response properties of the ventral striatum. In this study, we used fMRI in five neurosurgical patients with focal vmPFC lesions to test the hypothesis that the vmPFC is necessary for enhancing ventral striatum responses to the anticipation of reward. In support of this hypothesis, we found that, compared with age- and gender-matched neurologically healthy subjects, the vmPFC-lesioned patients had reduced ventral striatal activity during the anticipation of reward. Furthermore, we observed that the vmPFC-lesioned patients had decreased volumes of the accumbens subregion of the ventral striatum. Together, these functional and structural neuroimaging data provide novel evidence for a critical role for the vmPFC in contributing to reward-related activity of the ventral striatum. These results offer new insight into the functional and structural interactions between key components of the brain circuitry underlying human affective function and decision-making.

SIGNIFICANCE STATEMENT

Maladaptive decision-making is a common problem across multiple mental health disorders. Developing new pathophysiologically based strategies for diagnosis and treatment thus requires a better understanding of the brain circuits responsible for adaptive decision-making and related psychological subprocesses (e.g., reward valuation, anticipation, and motivation). Animal studies provide evidence that these functions are mediated through direct interactions between two key nodes of a posited "reward circuit," the ventral striatum and the ventromedial prefrontal cortex (vmPFC). For the first time in humans, we demonstrate that damage to the vmPFC results in decreased ventral striatum activity during reward anticipation. These data provide unique evidence on the causal mechanisms by which the vmPFC and ventral striatum interact during the anticipation of rewards.

Post-Learning Sleep Transiently Boosts Context Specific Operant Extinction Memory

Operant extinction is learning to supress a previously rewarded behavior. It is known to be strongly associated with the specific context in which it was acquired, which limits the therapeutic use of operant extinction in behavioral treatments, e.g., of addiction. We examined whether sleep influences contextual memory of operant extinction over time, using two different recall tests (Recent and Remote). Rats were trained in an operant conditioning task (lever press) in context A, then underwent extinction training in context B, followed by a 3-h retention period that contained either spontaneous morning sleep, morning sleep deprivation, or spontaneous evening wakefulness. A recall test was performed either immediately after the 3-h experimental retention period (Recent recall) or after 48 h (Remote), in the extinction context B and in a novel context C. The two main findings were: (i) at the Recent recall test, sleep in comparison with sleep deprivation and spontaneous wakefulness enhanced extinction memory but, only in the extinction context B; (ii) at the Remote recall, extinction performance after sleep was enhanced in both contexts B and C to an extent comparable to levels at Recent recall in context B. Interestingly, extinction performance at Remote recall was also improved in the sleep deprivation groups in both contexts, with no difference to performance in the sleep group. Our results suggest that 3 h of post-learning sleep transiently facilitate the context specificity of operant extinction at a Recent recall. However, the improvement and contextual generalization of operant extinction memory observed in the long-term, i.e., after 48 h, does not require immediate post-learning sleep.

Contemporary approaches to neural circuit manipulation and mapping: focus on reward and addiction

Tying complex psychological processes to precisely defined neural circuits is a major goal of systems and behavioural neuroscience. This is critical for understanding adaptive behaviour, and also how neural systems are altered in states of psychopathology, such as addiction. Efforts to relate psychological processes relevant to addiction to activity within defined neural circuits have been complicated by neural heterogeneity. Recent advances in technology allow for manipulation and mapping of genetically and anatomically defined neurons, which when used in concert with sophisticated behavioural models, have the potential to provide great insight into neural circuit bases of behaviour. Here we discuss contemporary approaches for understanding reward and addiction, with a focus on midbrain dopamine and cortico-striato-pallidal circuits.

Prefrontal cortical regulation of brainwide circuit dynamics and reward-related behavior

Motivation for reward drives adaptive behaviors, whereas impairment of reward perception and experience (anhedonia) can contribute to psychiatric diseases, including depression and schizophrenia. We sought to test the hypothesis that the medial prefrontal cortex (mPFC) controls interactions among specific subcortical regions that govern hedonic responses. By using optogenetic functional magnetic resonance imaging to locally manipulate but globally visualize neural activity in rats, we found that dopamine neuron stimulation drives striatal activity, whereas locally increased mPFC excitability reduces this striatal response and inhibits the behavioral drive for dopaminergic stimulation. This chronic mPFC overactivity also stably suppresses natural reward-motivated behaviors and induces specific new brainwide functional interactions, which predict the degree of anhedonia in individuals. These findings describe a mechanism by which mPFC modulates expression of reward-seeking behavior, by regulating the dynamical interactions between specific distant subcortical regions.

Differential roles of medial prefrontal subregions in the regulation of drug seeking

The prefrontal cortex plays an important role in shaping cognition and behavior. Many studies have shown that medial prefrontal cortex (mPFC) plays a key role in seeking, extinction, and reinstatement of cocaine seeking in rodent models of relapse. Subregions of mPFC appear to play distinct roles in these behaviors, such that the prelimbic cortex (PL) is proposed to drive cocaine seeking and the infralimbic cortex (IL) is proposed to suppress cocaine seeking after extinction. This dichotomy of mPFC function may be a general attribute, as similar dorsal-ventral distinctions exist for expression vs. extinction of fear conditioning. However, other results indicate that the role of mPFC neurons in reward processing is more complex than a simple PL-seek vs. IL-extinguish dichotomy. Both PL and IL have been shown to drive and inhibit drug seeking (and other types of behaviors) depending on a range of factors including the behavioral context, the drug-history of the animal, and the type of drug investigated. This heterogeneity of findings may reflect multiple subcircuits within each of these PFC areas supporting unique functions. It may also reflect the fact that the mPFC plays a multifaceted role in shaping cognition and behavior, including those overlapping with cocaine seeking and extinction. Here we discuss research leading to the hypothesis that dorsal and ventral mPFC differentially control drug seeking and extinction. We also present recent results calling the absolute nature of a PL vs. IL dichotomy into question. Finally, we consider alternate functions for mPFC that correspond less to response execution and inhibition and instead incorporate the complex cognitive behavior for which the mPFC is broadly appreciated.

Nucleus Accumbens and Posterior Amygdala Mediate Cue-Triggered Alcohol Seeking and Suppress Behavior During the Omission of Alcohol-Predictive Cues

Neurobiological mechanisms that influence behavior in the presence of alcohol-associated stimuli involve processes that organize behavior during the presence of these cues, and separately, regulation of behavior in their absence. However, little is known about anatomical structures that might mediate this regulation. Here we examined nucleus accumbens shell (AcbSh) as a possible neural substrate mediating behavior modulation triggered by the presence and absence of alcohol-associated environmental cues and contexts. We also examined subregions of basal amygdala nuclei- rostral basolateral (BLA) and basal posterior (BAP)- as they provide a major source of glutamatergic input to the AcbSh. Animals were trained to associate an auditory conditioning stimulus with alcohol in a discriminative context and then subsequently tested for conditioned port-entries across contexts either previously associated or not associated with alcohol. We found that, on test to the alcohol cue alone, AcbSh inactivation prevented conditioned port-entries in contexts that either were associated with alcohol or were novel, while also increasing unconditioned port-entries during the intertrial intervals. When tested to alcohol-reinforced cues, AcbSh inactivation produced more cue-trial omissions and elevated unconditioned port-entries. Interestingly, BLA and BAP inactivation produced dissociable effects. BAP but not BLA increased unconditioned port-entries, while both manipulations prevented conditioned port-entries during the alcohol-cue. We conclude that AcbSh is necessary for modulating control over behavior otherwise guided by the presence of alcohol-predictive environmental stimuli and contexts. Moreover, this role may involve integration of functionally segregated inputs from rostral and posterior portions of basal amygdala nuclei.

Prefrontal neurons encode context-based response execution and inhibition in reward seeking and extinction

The prefrontal cortex (PFC) guides execution and inhibition of behavior based on contextual demands. In rodents, the dorsal/prelimbic (PL) medial PFC (mPFC) is frequently considered essential for execution of goal-directed behavior ("go") whereas ventral/infralimbic (IL) mPFC is thought to control behavioral suppression ("stop"). This dichotomy is commonly seen for fear-related behaviors, and for some behaviors related to cocaine seeking. Overall, however, data for reward-directed behaviors are ambiguous, and few recordings of PL/IL activity have been performed to demonstrate single-neuron correlates. We recorded neuronal activity in PL and IL during discriminative stimulus driven sucrose seeking followed by multiple days of extinction of the reward-predicting stimulus. Contrary to a generalized PL-go/IL-stop hypothesis, we found cue-evoked activity in PL and IL during reward seeking and extinction. Upon analyzing this activity based on resultant behavior (lever press or withhold), we found that neurons in both areas encoded contextually appropriate behavioral initiation (during reward seeking) and withholding (during extinction), where context was dictated by response-outcome contingencies. Our results demonstrate that PL and IL signal contextual information for regulation of behavior, irrespective of whether that involves initiation or suppression of behavioral responses, rather than topographically encoding go vs. stop behaviors. The use of context to optimize behavior likely plays an important role in maximizing utility-promoting exertion of activity when behaviors are rewarded and conservation of energy when not.

Lateral hypothalamus, nucleus accumbens, and ventral pallidum roles in eating and hunger: interactions between homeostatic and reward circuitry

The study of the neural bases of eating behavior, hunger, and reward has consistently implicated the lateral hypothalamus (LH) and its interactions with mesocorticolimbic circuitry, such as mesolimbic dopamine projections to nucleus accumbens (NAc) and ventral pallidum (VP), in controlling motivation to eat. The NAc and VP play special roles in mediating the hedonic impact (“liking”) and motivational incentive salience (“wanting”) of food rewards, and their interactions with LH help permit regulatory hunger/satiety modulation of food motivation and reward. Here, we review some progress that has been made regarding this circuitry and its functions: the identification of localized anatomical hedonic hotspots within NAc and VP for enhancing hedonic impact; interactions of NAc/VP hedonic hotspots with specific LH signals such as orexin; an anterior-posterior gradient of sites in NAc shell for producing intense appetitive eating vs. intense fearful reactions; and anatomically distributed appetitive functions of dopamine and mu opioid signals in NAc shell and related structures. Such findings help improve our understanding of NAc, VP, and LH interactions in mediating affective and motivation functions, including “liking” and “wanting” for food rewards.

Biomarkers in substance use disorders

The prevention and treatment of substance use disorders (SUDs), including addiction, would benefit from having better biomarkers for the classification of patients into categories that are reproducible and have predictive validity. Direct measurement of drugs or their metabolites in various body fluids constitutes a clinically valuable biomarker but one that can only be used to corroborate acute or relatively recent drug use. Thus, there is an urgent need for biomarkers that reflect chronic drug exposure as well as biomarkers that predict or correlate with disease trajectories and treatment responses. Advances in tools and technologies to investigate genetics, epigenetics and epitranscriptomics, and human brain function and neurochemistry (brain imaging tools including EEG) offer unprecedented opportunities for the development of such biomarkers. Progress in this area will not only enhance our ability to screen and treat patients with SUDs but also accelerate research on the neurobiological processes that underlie SUDs.

Frontostriatal systems comprising connections between ventral medial prefrontal cortex and nucleus accumbens subregions differentially regulate motor impulse control in rats

RATIONALE

Deficits in impulse control are prevalent in several neuropsychiatric disorders that are based on impaired frontostriatal communication. The ventral medial prefrontal cortex (vmPFC) and the nucleus accumbens (NAc) are key substrates of impulse control in rats. The NAc core and shell are considered to be differentially involved suggesting a functional distinction between the connections of the vmPFC and particular NAc subregions concerning impulse control.

OBJECTIVES/METHODS

In the present study, simultaneous inactivation of the rats' vmPFC and NAc core or shell by contralateral microinfusion of the GABAA receptor agonist muscimol was used to investigate their relevance for impulse control in the five-choice serial reaction time task (5-CSRTT).

RESULTS

Disconnection of the vmPFC and NAc shell produced specific impairments in inhibitory control, indicated by significantly increased premature responding and an enhanced number of time-out responses, closely resembling the effects of bilateral inactivation of either the vmPFC or NAc shell previously reported using the same task. In contrast, disconnection of the vmPFC and NAc core only slightly increased the rate of omissions and latency of reward collection indicating attentional and motivational deficits.

CONCLUSIONS

Our results extend previous findings indicating the functional specialisation of frontostriatal networks and show a differential contribution of specific vmPFC-NAc connections to behavioural control depending on the NAc subregion. We conclude that the regulation of impulse control in rats requires an intact connection between the vmPFC and the NAc shell, while the vmPFC-NAc core projection seems to be of minor importance.

Control Over Stress Accelerates Extinction of Drug Seeking Via Prefrontal Cortical Activation

Extinction is a form of inhibitory learning viewed as an essential process in suppressing conditioned responses to drug cues, yet there is little information concerning experiential variables that modulate its formation. Coping factors play an instrumental role in determining how adverse life events impact the transition from casual drug use to addiction. Here we provide evidence in rat that prior exposure to controllable stress accelerates the extinction of cocaine-seeking behavior relative to uncontrollable or no stress exposure. Subsequent experimentation using high-speed optogenetic tools determined if the infralimbic region (IL) of the ventral medial prefrontal cortex mediates the impact of controllable stress on cocaine-seeking behavior. Photoinhibition of pyramidal neurons in the IL during coping behavior did not interfere with subject's ability to control the stressor, but prevented the later control-induced facilitation of extinction. These results provide strong evidence that the degree of behavioral control over adverse events, rather than adverse events per se, potently modulates the extinction of cocaine-seeking behavior, and that controllable stress engages prefrontal circuitry that primes future extinction learning.

Inactivating the infralimbic but not prelimbic medial prefrontal cortex facilitates the extinction of appetitive Pavlovian conditioning in Long-Evans rats

The infralimbic medial prefrontal cortex (IL) has been posited as a common node in distinct neural circuits that mediate the extinction of appetitive and aversive conditioning. However, appetitive extinction is typically assessed using instrumental conditioning procedures, whereas the extinction of aversive conditioning is customarily studied using Pavlovian assays. The role of the IL in the extinction of appetitive Pavlovian conditioning remains underexplored. We investigated the involvement of the IL and prelimbic medial prefrontal cortex (PrL) in appetitive extinction in Pavlovian and instrumental conditioning assays in male, Long-Evans rats. Following acquisition, a gamma-aminobutyric acid agonist solution (0.03 nmol muscimol; 0.3 nmol baclofen; 0.3 μl/side) was bilaterally microinfused into the IL or PrL to pharmacologically inactivate each region before the first extinction session. Compared to saline, PrL inactivation did not affect the acquisition of extinction or the recall of extinction memory 24-h later. IL inactivation caused a more rapid extinction of Pavlovian conditioning, but had no effect on the extinction of instrumental conditioning or extinction recall. IL inactivation during a Pavlovian conditioning session in which conditioned stimulus (CS) trials were paired with sucrose did not affect CS-elicited behaviour, but increased responding during intervals that did not contain the CS. The same manipulation did not impact lever pressing for sucrose. These findings suggest that the IL may normally maintain Pavlovian conditioned responding when an anticipated appetitive CS is unexpectedly withheld, and that this region has distinct roles in the expression of Pavlovian conditioning when an appetitive unconditioned stimulus is either presented or omitted.

Enhanced performance of aged rats in contingency degradation and instrumental extinction tasks

Normal aging in rats affects behavioral performance on a variety of associative learning tasks under Pavlovian conditions. There is little information, however, on whether aging also impacts performance of instrumental tasks. Young (9-12 months) and aged (24-27 months) Fisher 344 rats were trained to press distinct levers associated with either maltodextrin or sucrose. The rats in both age groups increased their lever press frequency at a similar rate, suggesting that the initial acquisition of this instrumental task is not affected by aging. Using a contingency degradation procedure, we then addressed whether aged rats could adapt their behavior to changes in action-outcome contingencies. We found that young and aged rats do adapt, but that a different schedule of reinforcement is necessary to optimize performance in each age group. Finally, we also addressed whether aged rats can extinguish a lever press action as well as young rats, using 2 40-min extinction sessions on consecutive days. While extinction profiles were similar in young and aged rats on the first day of training, aged rats were faster to extinguish their lever presses on the second day, in spite of their performance levels being similar at the beginning of the session. Together these data support the finding that acquisition of instrumental lever press behaviors is preserved in aged rats and suggest that they have a different threshold for switching strategies in response to changes in action-outcome associations. This pattern of result implies that age-related changes in the brain are heterogeneous and widespread across structures.

Orbitofrontal cortical neurons encode expectation-driven initiation of reward-seeking

Adaptive execution and inhibition of behavior are guided by the activity of neuronal populations across multiple frontal cortical areas. The rodent medial prefrontal cortex has been well studied with respect to these behaviors, influencing behavioral execution/inhibition based on context. Other frontal regions, in particular the orbitofrontal cortex (OFC), are critical in directing behavior to obtain rewards, but the relationship between OFC neuronal activity and response execution or inhibition has been poorly characterized. In particular, little is known about OFC with respect to extinction learning, an important example of context-guided response inhibition. Here, we recorded the activity of OFC neurons while rats performed a discriminative-stimulus (DS)-driven sucrose-seeking task followed by multiple days of extinction of the DS. OFC neuronal activity was maximally responsive (1) to reward-predicting stimuli (RS) that triggered a lever press (i.e., lever-response initiation) and (2) during reward-well approach in pursuit of sucrose (i.e., well-response initiation). RS presentation that was not followed by a lever press or RS presentation during extinction produced weak activation, as did nonrewarded stimulus (NS) presentation regardless of response (press or withhold) or session (DS-sucrose or extinction). Activity related to nonrewarded well entry was minor, and activity was significantly inhibited during reward consumption. Finally, OFC neuronal activity switched selectivity to track rewarded behaviors when the RS/NS contingencies were reversed. Thus, rather than signaling variables related to extinction or response inhibition, activity in OFC was strongest at the initiation of multiple components of reward-seeking behavior, most prominently when valid reward-predicting cues drove these behaviors.

Differential contributions of infralimbic prefrontal cortex and nucleus accumbens during reward-based learning and extinction

Using environmental cues for the prediction of future events is essential for survival. Such cue-outcome associations are thought to depend on mesolimbic circuitry involving the nucleus accumbens (NAc) and prefrontal cortex (PFC). Several studies have identified roles for both NAc and PFC in the expression of stable goal-directed behaviors, but much remains unknown about their roles during learning of such behaviors. To further address this question, we used in vivo oxygen amperometry, a proxy for blood oxygen level-dependent (BOLD) signal measurement in human functional magnetic resonance imaging, in rats performing a cued lever-pressing task requiring discrimination between a rewarded and nonrewarded cue. Simultaneous oxygen recordings were obtained from infralimbic PFC (IFC) and NAc throughout both acquisition and extinction of this task. Activation of NAc was specifically observed following rewarded cue onset during the entire acquisition phase and also during the first days of extinction. In contrast, IFC activated only during the earliest periods of acquisition and extinction, more specifically to the nonrewarded cue. Thus, in vivo oxygen amperometry permits a novel, stable form of longitudinal analysis of brain activity in behaving animals, allowing dissociation of the roles of different brain regions over time during learning of reward-driven instrumental action. The present results offer a unique temporal perspective on how NAc may promote actions directed toward anticipated positive outcome throughout learning, while IFC might suppress actions that no longer result in reward, but only during critical periods of learning.