Opposing effects of amygdala and orbital prefrontal cortex lesions on the extinction of instrumental responding in macaque monkeys

Understanding the heterogeneity of anxiety using a translational neuroscience approach

Anxiety disorders affect millions of people worldwide and present a challenge in neuroscience research because of their substantial heterogeneity in clinical presentation. While a great deal of progress has been made in understanding the neurobiology of fear and anxiety, these insights have not led to effective treatments. Understanding the relationship between phenotypic heterogeneity and the underlying biology is a critical first step in solving this problem. We show translation, reverse translation, and computational modeling can contribute to a refined, cross-species understanding of fear and anxiety as well as anxiety disorders. More specifically, we outline how animal models can be leveraged to develop testable hypotheses in humans by using targeted, cross-species approaches and ethologically informed behavioral paradigms. We discuss reverse translational approaches that can guide and prioritize animal research in nontraditional research species. Finally, we advocate for the use of computational models to harmonize cross-species and cross-methodology research into anxiety. Together, this translational neuroscience approach will help to bridge the widening gap between how we currently conceptualize and diagnose anxiety disorders, as well as aid in the discovery of better treatments for these conditions.

Prefrontal influences on the function of the neural circuitry underlying anxious temperament in primates

Anxious temperament, characterized by heightened behavioral and physiological reactivity to potential threat, is an early childhood risk factor for the later development of stress-related psychopathology. Using a well-validated nonhuman primate model, we tested the hypothesis that the prefrontal cortex (PFC) is critical in regulating the expression of primate anxiety-like behavior, as well as the function of subcortical components of the anxiety-related neural circuit. We performed aspiration lesions of a narrow 'strip' of the posterior orbitofrontal cortex (OFC) intended to disrupt both cortex and axons entering, exiting and coursing through the pOFC, particularly those of the uncinate fasciculus (UF), a white matter tract that courses adjacent to and through this region. The OFC is of particular interest as a potential regulatory region because of its extensive reciprocal connections with amygdala, other subcortical structures and other frontal lobe regions. We validated this lesion method by demonstrating marked lesion-induced decreases in the microstructural integrity of the UF, which contains most of the fibers that connect the ventral PFC with temporal lobe structures as well as with other frontal regions. While the lesions resulted in modest decreases in threat-related behavior, they substantially decreased metabolism in components of the circuit underlying threat processing. These findings provide evidence for the importance of structural connectivity between the PFC and key subcortical structures in regulating the functions of brain regions known to be involved in the adaptive and maladaptive expression of anxiety.

Contributions of anterior cingulate cortex and basolateral amygdala to decision confidence and learning under uncertainty

The subjective sense of certainty, or confidence, in ambiguous sensory cues can alter the interpretation of reward feedback and facilitate learning. We trained rats to report the orientation of ambiguous visual stimuli according to a spatial stimulus-response rule that must be learned. Following choice, rats could wait a self-timed delay for reward or initiate a new trial. Waiting times increase with discrimination accuracy, demonstrating that this measure can be used as a proxy for confidence. Chemogenetic silencing of BLA shortens waiting times overall whereas ACC inhibition renders waiting times insensitive to confidence-modulating attributes of visual stimuli, suggesting contribution of ACC but not BLA to confidence computations. Subsequent reversal learning is enhanced by confidence. Both ACC and BLA inhibition block this enhancement but via differential adjustments in learning strategies and consistent use of learned rules. Altogether, we demonstrate dissociable roles for ACC and BLA in transmitting confidence and learning under uncertainty.

Inhibitory control in BALB/c mice sub-strains during extinction learning

Dysregulation of executive function (EF) involves alterations in cognitive flexibility / control and is underscored by learning impairments in neurodevelopmental disorders. Here, we examine cognitive inflexibility in BALB/cJ mice (a mouse model showing diminished sociability, increased anxiety and inattentive behaviour) and closely related "reference" BALB/cByJ mice. We used an appetitive extinction paradigm to investigate if cognitive flexibility measures are different between learning acquisition and extinction. The two BALB/c sub-strains learned to respond to a stimulus in a touchscreen operant chamber, after which the reward was removed and responses should be inhibited. Both mice sub-strains showed a different rate of learning while acquiring the task, in which the BALB/cJ mice were faster learners compared to the BALB/cByJ mice. This was not observed during the extinction phase, in which the BALB/cJ mice were able to extinguish responding to unrewarded stimuli equally. Within the BALB/cJ sub-strain, variation in the ability to inhibit a learnt response was observed when comparing them to similar grouped BALB/cByJ mice: BALB/cJ animals that reached the criterion were more reward driven, while BALB/cJ mice failing to reach the set criterion during extinction processing make more mistakes. Additionally, the changes observed during acquisition, were driven by animals not reaching the extinction criterion. Our results suggest that the BALB/c mice sub-strains may use different strategies to learn during appetitive extinction. This may be useful in the phenotypic dissection of cognitive flexibility in BALB/c sub-strains and their mapping on genetic variance revealed by next-generation sequencing in future studies.

The role of prefrontal-subcortical circuitry in negative bias in anxiety: Translational, developmental and treatment perspectives

Anxiety disorders are the most common cause of mental ill health in the developed world, but our understanding of symptoms and treatments is not presently grounded in knowledge of the underlying neurobiological mechanisms. In this review, we discuss accumulating work that points to a role for prefrontal-subcortical brain circuitry in driving a core psychological symptom of anxiety disorders - negative affective bias. Specifically, we point to converging work across humans and animal models, suggesting a reciprocal relationship between dorsal and ventral prefrontal-amygdala circuits in promoting and inhibiting negative bias, respectively. We discuss how the developmental trajectory of these circuits may lead to the onset of anxiety during adolescence and, moreover, how effective pharmacological and psychological treatments may serve to shift the balance of activity within this circuitry to ameliorate negative bias symptoms. Together, these findings may bring us closer to a mechanistic, neurobiological understanding of anxiety disorders and their treatment.

Altered function but not structure of the amygdala in nicotine-dependent individuals

Tobacco use disorder is frequently comorbid with emotional disorders, each exerting reciprocal influence on the other. As an important hub for emotional processing, amygdala may also play a critical role in tobacco addiction. Therefore, we aimed to investigate the volume and spontaneous activity of the amygdala in nicotine-dependent individuals and their relationships with cigarette use. A total of 84 smokers (aged 22-54 years) and 41 nonsmokers (aged 26-56 years) were enrolled in the present study. 3D-T1 weighted images and resting-state fMRI images were acquired from all participants. We used ROI-wise volume, fractional amplitude of low frequency fluctuation (fALFF) and resting-state functional connectivity (FC) to assess structural and functional changes of the amygdala in the smokers. There was no significant difference between smokers and nonsmokers on amygdala volume (p > 0.05). When compared to nonsmokers, increased fALFF in the right amygdala was observed in smokers (p = 0.024). In addition, increased FC between the left amygdala and the right precuneus and decreased FC between the right amygdala and the right orbitofrontal cortex (OFC) was found in smokers. In smokers, these amygdala measures did not correlate with any measures of cigarette use. The results revealed that the amygdala function but not volume was affected in nicotine addiction. When considering the fALFF and FC results, we propose that the OFC top-down control may regulate the amygdala activity in nicotine addicts. The pattern of amygdala-based FC in smokers revealed in our study may provide new information about the brain circuitry of tobacco dependence.

Role of the Perigenual Anterior Cingulate and Orbitofrontal Cortex in Contingency Learning in the Marmoset

Two learning mechanisms contribute to decision-making: goal-directed actions and the "habit" system, by which action-outcome and stimulus-response associations are formed, respectively. Rodent lesion studies and human neuroimaging have implicated both the medial prefrontal cortex (mPFC) and the orbitofrontal cortex (OFC) in the neural basis of contingency learning, a critical component of goal-directed actions, though some published findings are conflicting. We sought to reconcile the existing literature by comparing the effects of excitotoxic lesions of the perigenual anterior cingulate cortex (pgACC), a region of the mPFC, and OFC on contingency learning in the marmoset monkey using a touchscreen-based paradigm, in which the contingent relationship between one of a pair of actions and its outcome was degraded selectively. Both the pgACC and OFC lesion groups were insensitive to the contingency degradation, whereas the control group demonstrated selectively higher performance of the nondegraded action when compared with the degraded action. These findings suggest the pgACC and OFC are both necessary for normal contingency learning and therefore goal-directed behavior.

The Role of Frontal Cortical and Medial-Temporal Lobe Brain Areas in Learning a Bayesian Prior Belief on Reversals

Reversal learning has been extensively studied across species as a task that indexes the ability to flexibly make and reverse deterministic stimulus-reward associations. Although various brain lesions have been found to affect performance on this task, the behavioral processes affected by these lesions have not yet been determined. This task includes at least two kinds of learning. First, subjects have to learn and reverse stimulus-reward associations in each block of trials. Second, subjects become more proficient at reversing choice preferences as they experience more reversals. We have developed a Bayesian approach to separately characterize these two learning processes. Reversal of choice behavior within each block is driven by a combination of evidence that a reversal has occurred, and a prior belief in reversals that evolves with experience across blocks. We applied the approach to behavior obtained from 89 macaques, comprising 12 lesion groups and a control group. We found that animals from all of the groups reversed more quickly as they experienced more reversals, and correspondingly they updated their prior beliefs about reversals at the same rate. However, the initial values of the priors that the various groups of animals brought to the task differed significantly, and it was these initial priors that led to the differences in behavior. Thus, by taking a Bayesian approach we find that variability in reversal-learning performance attributable to different neural systems is primarily driven by different prior beliefs about reversals that each group brings to the task.

SIGNIFICANCE STATEMENT

The ability to use prior knowledge to adapt choice behavior is critical for flexible decision making. Reversal learning is often studied as a form of flexible decision making. However, prior studies have not identified which brain regions are important for the formation and use of prior beliefs to guide choice behavior. Here we develop a Bayesian approach that formally characterizes learning set as a concept, and we show that, in macaque monkeys, the amygdala and medial prefrontal cortex have a role in establishing an initial belief about the stability of the reward environment.

The basolateral amygdala in reward learning and addiction

Sophisticated behavioral paradigms partnered with the emergence of increasingly selective techniques to target the basolateral amygdala (BLA) have resulted in an enhanced understanding of the role of this nucleus in learning and using reward information. Due to the wide variety of behavioral approaches many questions remain on the circumscribed role of BLA in appetitive behavior. In this review, we integrate conclusions of BLA function in reward-related behavior using traditional interference techniques (lesion, pharmacological inactivation) with those using newer methodological approaches in experimental animals that allow in vivo manipulation of cell type-specific populations and neural recordings. Secondly, from a review of appetitive behavioral tasks in rodents and monkeys and recent computational models of reward procurement, we derive evidence for BLA as a neural integrator of reward value, history, and cost parameters. Taken together, BLA codes specific and temporally dynamic outcome representations in a distributed network to orchestrate adaptive responses. We provide evidence that experiences with opiates and psychostimulants alter these outcome representations in BLA, resulting in long-term modified action.

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.

A role for primate subgenual cingulate cortex in sustaining autonomic arousal

The subgenual anterior cingulate cortex (subgenual ACC) plays an important role in regulating emotion, and degeneration in this area correlates with depressed mood and anhedonia. Despite this understanding, it remains unknown how this part of the prefrontal cortex causally contributes to emotion, especially positive emotions. Using Pavlovian conditioning procedures in macaque monkeys, we examined the contribution of the subgenual ACC to autonomic arousal associated with positive emotional events. After such conditioning, autonomic arousal increases in response to cues that predict rewards, and monkeys maintain this heightened state of arousal during an interval before reward delivery. Here we show that although monkeys with lesions of the subgenual ACC show the initial, cue-evoked arousal, they fail to sustain a high level of arousal until the anticipated reward is delivered. Control procedures showed that this impairment did not result from differences in autonomic responses to reward delivery alone, an inability to learn the association between cues and rewards, or to alterations in the light reflex. Our data indicate that the subgenual ACC may contribute to positive affect by sustaining arousal in anticipation of positive emotional events. A failure to maintain positive affect for expected pleasurable events could provide insight into the pathophysiology of psychological disorders in which negative emotions dominate a patient's affective experience.

Animal models of obsessive-compulsive spectrum disorders

Obsessive-compulsive disorder (OCD) and related conditions (trichotillomania, pathological skin-picking, pathological nail-biting) are common and disabling. Current treatment approaches fail to help a significant proportion of patients. Multiple tiers of evidence link these conditions with underlying dysregulation of particular cortico-subcortical circuitry and monoamine systems, which represent targets for treatment. Animal models designed to capture aspects of these conditions are critical for several reasons. First, they help in furthering our understanding of neuroanatomical and neurochemical underpinnings of the obsessive-compulsive (OC) spectrum. Second, they help to account for the brain mechanisms by which existing treatments (pharmacotherapy, psychotherapy, deep brain stimulation) exert their beneficial effects on patients. Third, they inform the search for novel treatments. This article provides a critique of key animal models for selected OC spectrum disorders, beginning with initial work relating to anxiety, but moving on to recent developments in domains of genetic, pharmacological, cognitive, and ethological models. We find that there is a burgeoning literature in these areas with important ramifications, which are considered, along with salient future lines of research.

Neural estimates of imagined outcomes in the orbitofrontal cortex drive behavior and learning

Imagination, defined as the ability to interpret reality in ways that diverge from past experience, is fundamental to adaptive behavior. This can be seen at a simple level in our capacity to predict novel outcomes in new situations. The ability to anticipate outcomes never before received can also influence learning if those imagined outcomes are not received. The orbitofrontal cortex is a key candidate for where the process of imagining likely outcomes occurs; however, its precise role in generating these estimates and applying them to learning remain open questions. Here we address these questions by showing that single-unit activity in the orbitofrontal cortex reflects novel outcome estimates. The strength of these neural correlates predicted both behavior and learning, learning that was abolished by temporally specific inhibition of orbitofrontal neurons. These results are consistent with the proposal that the orbitofrontal cortex is critical for integrating information to imagine future outcomes.

Network connectivity modulates power spectrum scale invariance

Measures of complexity are sensitive in detecting disease, which has made them attractive candidates for diagnostic biomarkers; one complexity measure that has shown promise in fMRI is power spectrum scale invariance (PSSI). Even if scale-free features of neuroimaging turn out to be diagnostically useful, however, their underlying neurobiological basis is poorly understood. Using modeling and simulations of a schematic prefrontal-limbic meso-circuit, with excitatory and inhibitory networks of nodes, we present here a framework for how network density within a control system can affect the complexity of signal outputs. Our model demonstrates that scale-free behavior, similar to that observed in fMRI PSSI data, can be obtained for sufficiently large networks in a context as simple as a linear stochastic system of differential equations, although the scale-free range improves when introducing more realistic, nonlinear behavior in the system. PSSI values (reflective of complexity) vary as a function of both input type (excitatory, inhibitory) and input density (mean number of long-range connections, or strength), independent of their node-specific geometric distribution. Signals show pink noise (1/f) behavior when excitatory and inhibitory influences are balanced. As excitatory inputs are increased and decreased, signals shift towards white and brown noise, respectively. As inhibitory inputs are increased and decreased, signals shift towards brown and white noise, respectively. The results hold qualitatively at the hemodynamic scale, which we modeled by introducing a neurovascular component. Comparing hemodynamic simulation results to fMRI PSSI results from 96 individuals across a wide spectrum of anxiety-levels, we show how our model can generate concrete and testable hypotheses for understanding how connectivity affects regulation of meso-circuits in the brain.

Orbitofrontal cortex inactivation impairs between- but not within-session Pavlovian extinction: an associative analysis

The orbitofrontal cortex (OFC) is argued to be the neural locus of Pavlovian outcome expectancies. Reinforcement learning theories argue that extinction learning in Pavlovian procedures is caused by the discrepancy between the expected value of the outcome (US) that is elicited by a predictive stimulus (CS), and the lack of experienced US. If the OFC represents Pavlovian outcome expectancies that are necessary for extinction learning, then disrupting OFC function prior to extinction training should impair extinction learning. This was tested. In experiment 1, Long Evans rats received infusions of saline or muscimol targeting the lateral OFC prior to three appetitive Pavlovian extinction sessions. Muscimol infused into the OFC disrupted between-session but not within-session extinction behaviour. This finding was not due to muscimol infusions disrupting the memory consolidation process per se as there was no effect of muscimol infusion when administered immediately post session (experiment 2). These findings support a role for the OFC in representing outcome expectancies that are necessary for learning. A number of ways in which disrupting outcome expectancy information might block learning will be discussed in the context of traditional associative learning theories and the associative structures they depend on.

Prenatal cocaine exposure alters functional activation in the ventral prefrontal cortex and its structural connectivity with the amygdala

Prenatal cocaine exposure (PCE) is associated with arousal dysregulation, and alterations of amygdala activity in response to emotional arousal have previously been reported. However, voluntary regulation of emotional affect, enabling appropriate neural response to different streams of stimuli, must also engage prefrontal regions, yet the impact of PCE on these prefrontal mechanisms has not been investigated. Recent neuroimaging studies have shown the involvement of ventral prefrontal cortex (vPFC) in the modulation of amygdala reactivity and the mediation of effective emotional regulation. Based on these findings, using functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), the present study compared functional activations of the vPFC as well as its structural connectivity with the amygdala between groups of PCE and control adolescents. In a working memory task with emotional distracters, the PCE adolescents exhibited less capability of increasing their vPFC activation in response to increased memory load, which corresponded with their less suppressed amygdala activation. Reduced structural connectivity between the vPFC and the amygdala was also observed from DTI measurement in the PCE group. In addition, correlations between amygdala activation and (i) vPFC activation, as well as (ii) amygdala-vPFC structural connectivity, were observed in the control but not in the PCE group. These data complement previous findings of the impact of PCE on the activity of the amygdala and extend our understanding of the neurobiological mechanisms underlying the effect of PCE on arousal dysregulation reported in human and animal studies.

Repeated acquisition and discrimination reversal in the squirrel monkey (Saimiri sciureus)

Repeated acquisition and discrimination reversal tasks are often used to examine behavioral relations of, respectively, learning and cognitive flexibility. Surprisingly, despite their frequent use in cognitive neuroscience and behavioral pharmacology, variables that control performance under these two tasks have not been widely studied. The present studies were conducted to directly investigate the controlling variables in nonhuman primates. Squirrel monkeys were trained with a touchscreen variant of the repeated acquisition task in which a novel pair of S(+)/S(-) stimuli was presented daily. Subjects learned to discriminate the two stimuli (acquisition) and, subsequently, with the contingencies switched (reversal). Results indicate that rates of both acquisition and reversal learning increased across successive sessions, but that rate of reversal learning remained slower than acquisition learning, i.e., more trials were needed for mastery. Subsequent experiments showed this difference between the rate of learning novel discriminations and reversal was reliable for at least 5 days between acquisition and reversal and notwithstanding the interpolation of additional discriminations. Experimental analysis of the S(+)/S(-) elements of the tasks revealed that the difference in the rate of learning could not be attributed to a relatively aversive quality of the S(-) or to a relatively appetitive quality of the S(+), but, rather, to contextual control by the S(+)/S(-) stimulus complex. Thus, if either element (S(+) or S(-)) of the stimulus complex was replaced by a novel stimulus, the rate of acquisition approximated that expected with a novel stimulus pair. These results improve our understanding of fundamental features of discrimination acquisition and reversal.

Age-related similarities and differences in brain activity underlying reversal learning

The ability to update associative memory is an important aspect of episodic memory and a critical skill for social adaptation. Previous research with younger adults suggests that emotional arousal alters brain mechanisms underlying memory updating; however, it is unclear whether this applies to older adults. Given that the ability to update associative information declines with age, it is important to understand how emotion modulates the brain processes underlying memory updating in older adults. The current study investigated this question using reversal learning tasks, where younger and older participants (age ranges 19–35 and 61–78, respectively) learn a stimulus–outcome association and then update their response when contingencies change. We found that younger and older adults showed similar patterns of activation in the frontopolar OFC and the amygdala during emotional reversal learning. In contrast, when reversal learning did not involve emotion, older adults showed greater parietal cortex activity than did younger adults. Thus, younger and older adults show more similarities in brain activity during memory updating involving emotional stimuli than during memory updating not involving emotional stimuli.

Hippocampal activation during extinction learning predicts occurrence of the renewal effect in extinction recall

The renewal effect describes the reoccurrence of a previously extinguished response in situations where the context of extinction differs from that of acquisition, thus illustrating the context-dependency of extinction learning. A number of studies on contextual fear extinction have implicated hippocampus and vmPFC in processing and retrieval of context both during extinction learning and recall of extinction. In this functional magnetic resonance imaging (fMRI) study we explored the neural correlates of the renewal effect in associative learning, using a predictive learning task that required participants to learn relations between cues and outcomes presented in particular contexts. During extinction in a novel context, compared to extinction in a context identical to the acquisition context, participants who exhibited the renewal effect (REN) showed increased activation in brain regions including bilateral posterior hippocampus and left parahippocampal gyrus. This activation pattern was absent in participants that did not show the renewal effect (NOREN). In direct comparisons between the groups, the REN group exhibited higher activation in bilateral hippocampus, while the NOREN group showed higher activation in left dlPFC (BA 46) and right anterior cingulate (BA 32). During extinction recall, stimuli that had been extinguished in a different context were again presented in the context of acquisition. Here both groups exhibited predominantly prefrontal activation, with the REN group's focus upon bilateral OFC (BA 47) and bilateral vmPFC (BA 10), while the NOREN group showed generally more widespread activation, predominantly in large clusters of dlPFC (BA 8,9,45). In a direct comparison, the REN group showed higher activation than the NOREN group in left vmPFC (BA 10), while NOREN participants exhibited more activation in dlPFC (BA 9, 46). Activation in left vmPFC during extinction recall correlated with the number of renewal effect responses, while the dlPFC activation showed a negative correlation with renewal effect responses. These results highlight the differential activation patterns of processes that will eventually produce or not produce a renewal effect, indicating that during extinction learning hippocampus encodes the relation between context and cue-outcome, while in extinction recall vmPFC is active to retrieve this association.

Basolateral amygdala lesions facilitate reward choices after negative feedback in rats

The orbitofrontal cortex (OFC) and basolateral amygdala (BLA) constitute part of a neural circuit important for adaptive, goal-directed learning. One task measuring flexibility of response to changes in reward is discrimination reversal learning. Damage to OFC produces well documented impairments on various forms of reversal learning in rodents, monkeys, and humans. Recent reports show that BLA, though highly interconnected with OFC, may be differentially involved in reversal learning. In the present experiment, we compared the effects of bilateral, ibotenic acid lesions of OFC or BLA (or SHAM) on visual discrimination and reversal learning. Specifically, we used pairwise visual discrimination methods, as is commonly administered in non-human primate studies, and analyzed how animals use positive and negative trial-by-trial feedback, domains not previously explored in a rat study. As expected, OFC lesions displayed significantly slower reversal learning than SHAM and BLA rats across sessions. Rats with BLA lesions, conversely, showed facilitated reversal learning relative to SHAM and OFC groups. Furthermore, a trial-by-trial analysis of the errors committed showed the BLA group benefited more from incorrectly performed trials (or negative feedback) on future choices than either SHAM or OFC rats. This provides evidence that BLA and OFC are involved in updating responses to changes in reward contingency and that the roles are distinct. Our results are discussed in relation to a competitive framework model for OFC and BLA in reward processing.

Both younger and older adults have difficulty updating emotional memories

OBJECTIVE

The main purpose of the study was to examine whether emotion impairs associative memory for previously seen items in older adults, as previously observed in younger adults.

METHOD

Thirty-two younger adults and 32 older adults participated. The experiment consisted of 2 parts. In Part 1, participants learned picture-object associations for negative and neutral pictures. In Part 2, they learned picture-location associations for negative and neutral pictures; half of these pictures were seen in Part 1 whereas the other half were new. The dependent measure was how many locations of negative versus neutral items in the new versus old categories participants remembered in Part 2.

RESULTS

Both groups had more difficulty learning the locations of old negative pictures than of new negative pictures. However, this pattern was not observed for neutral items.

DISCUSSION

Despite the fact that older adults showed overall decline in associative memory, the impairing effect of emotion on updating associative memory was similar between younger and older adults.

Differential effects of serotonin-specific and excitotoxic lesions of OFC on conditioned reinforcer devaluation and extinction in rats

The orbitofrontal cortex (OFC) is critical for behavioral adaptation in response to changes in reward value. Here we investigated, in rats, the role of OFC and, specifically, serotonergic neurotransmission within OFC in a reinforcer devaluation task (which measures behavioral flexibility). This task used two visual cues, each predicting one of two foods, with the spatial position (left-right) of the cues above two levers pseudorandomized across trials. An instrumental action (lever press) was required for reinforcer delivery. After training, rats received either excitotoxic OFC lesions made by NMDA (N-methyl-d-aspartic acid), serotonin-specific OFC lesions made by 5,7-DHT (5,7-dihydroxytryptamine), or sham lesions. In sham-lesioned rats, devaluation of one food (by feeding to satiety) significantly decreased responding to the cue associated with that food, when both cues were presented simultaneously during extinction. Both types of OFC lesions disrupted the devaluation effect. In contrast, extinction learning was not affected by serotonin-specific lesions and was only mildly retarded in rats with excitotoxic lesions. Thus, serotonin within OFC is necessary for appropriately adjusting behavior toward cues that predict reward but not for reducing responses in the absence of reward. Our results are the first to demonstrate that serotonin in OFC is necessary for reinforcer devaluation, but not extinction.

Upregulation of the neuronal Per-Arnt-Sim domain protein 4 (Npas4) in the rat corticolimbic system following focal cerebral ischemia

The neuronal Per-Arnt-Sim domain protein 4 (Npas4) is an important transcriptional regulator of synaptic plasticity and cognition. The present study characterises the in vivo neuroanatomical expression pattern of the Npas4 protein in a rat model of focal cerebral ischemia. Animals were subjected to unilateral middle cerebral artery occlusion for 2 h, after which the spatiotemporal and neuronal profiles of Npas4 protein expression were analysed by immunohistochemistry at different time points post-reperfusion. Focal cerebral ischemia induced an early, transient and robust upregulation of Npas4 in a brain region-dependent manner involving predominantly principal neurons. Interestingly, we observed a unique differential induction of Npas4 protein expression in corticolimbic regions of the rat brain that are critically linked to cognition and emotion. These findings suggest that stroke-induced Npas4 upregulation may be involved in a transcriptional regulatory program within the corticolimbic circuitry following an ischemic insult.

Differential effects of amygdala, orbital prefrontal cortex, and prelimbic cortex lesions on goal-directed behavior in rhesus macaques

We assessed the involvement of the orbital prefrontal cortex (PFo), the prelimbic region of the medial prefrontal cortex (PL), and the amygdala in goal-directed behavior. Rhesus monkeys were trained on a task in which two different instrumental responses were linked to two different outcomes. One response, called "tap," required the monkeys to repeatedly touch a colored square on a video monitor to produce one kind of food reward. The other response, called "hold," required persistent contact of an identical stimulus, and it produced a different kind of food reward. After training, we assessed the effects of sensory-specific reinforcer devaluation as a way to probe each monkey's use of goal-directed behavior. In this procedure, monkeys were allowed to consume one of the two foods to satiety and were then tested for tap/hold preference under extinction. Unoperated control monkeys showed a reduction in the response associated with obtaining the devalued food, called the "devaluation effect," a hallmark of goal-directed behavior. Monkeys with bilateral lesions of PFo or the amygdala exhibited significantly reduced devaluation effects. Results from monkeys with PL lesions were equivocal. We conclude that both PFo and the amygdala play a significant role in goal-directed behavior in monkeys. Notably, the findings for PFo challenge the idea that orbital and medial prefrontal regions are exclusively dedicated to object- and action-based processes, respectively.

Aversive-bias and stage-selectivity in neurons of the primate amygdala during acquisition, extinction, and overnight retention

Extensive evidence implicates the amygdala as a major station for acquisition, extinction, and consolidation of emotional memories. Most of this work relies on fear-conditioning in rodents and imaging in humans. Few studies have explored coding of value in the primate amygdala, but the circuitry that underlies extinction and overnight retention remains largely unexplored. We developed a learning paradigm for nonhuman primates (macaca fascicularis) and recorded the activity of single neurons during the different stages of acquisition, extinction, and overnight consolidation of pleasant and aversive tone-odor associations. We find that many neurons become phase-locked to respiratory cycles in a stage-dependent manner, emphasizing the flexibility of amygdala neurons to represent the current state and change their spontaneous activity accordingly. We suggest that these changes can serve to increase neuronal sensitivity to an upcoming event and facilitate learning mechanisms. We further show formation of aversive-bias during the acquisition of associations and during overnight retention, in the sense that neurons preferentially code for the aversive conditioned stimuli, even if they initially homogenously represent value of the reinforcer. Our findings show flexible representations in the primate amygdala during the different cycles of learning and memory, and suggest selective potentiation of aversive information.

Differential brain activity during emotional versus nonemotional reversal learning

The ability to change an established stimulus-behavior association based on feedback is critical for adaptive social behaviors. This ability has been examined in reversal learning tasks, where participants first learn a stimulus-response association (e.g., select a particular object to get a reward) and then need to alter their response when reinforcement contingencies change. Although substantial evidence demonstrates that the OFC is a critical region for reversal learning, previous studies have not distinguished reversal learning for emotional associations from neutral associations. The current study examined whether OFC plays similar roles in emotional versus neutral reversal learning. The OFC showed greater activity during reversals of stimulus-outcome associations for negative outcomes than for neutral outcomes. Similar OFC activity was also observed during reversals involving positive outcomes. Furthermore, OFC activity is more inversely correlated with amygdala activity during negative reversals than during neutral reversals. Overall, our results indicate that the OFC is more activated by emotional than neutral reversal learning and that OFC's interactions with the amygdala are greater for negative than neutral reversal learning.

Amygdala lesions in rhesus monkeys fail to disrupt object choices based on internal context

We assessed the involvement of the amygdala in a task in which object choices were guided by internal context. Rhesus monkeys were trained on a biconditional discrimination whereby objects associated with food (but not water) were baited when the monkey was hungry, and objects associated with water (but not food) were baited when the monkey was thirsty. To solve this task, monkeys were required to choose objects yielding the reward congruent with their internal motivational state. Lesions of the amygdala did not disrupt learning or performance of this task. We conclude that the involvement of the amygdala in selective-satiation tasks, which depends in part on a change in internal context, is not due to the amygdala playing a general role in representing, or using, internal context.

Balkanizing the primate orbitofrontal cortex: distinct subregions for comparing and contrasting values

The primate orbitofrontal cortex (OFC) is often treated as a single entity, but architectonic and connectional neuroanatomy indicate that it has distinguishable parts. Nevertheless, few studies have attempted to dissociate the functions of its subregions. Here we review findings from recent neuropsychological and neurophysiological studies that do so. The lateral OFC seems to be important for learning, representing, and updating specific object-reward associations. The medial OFC seems to be important for value comparisons and choosing among objects on that basis. Rather than viewing this dissociation of function in terms of learning versus choosing, however, we suggest that it reflects the distinction between contrasts and comparisons: differences versus similarities. Making use of high-dimensional representations that arise from the convergence of several sensory modalities, the lateral OFC encodes contrasts among outcomes. The medial OFC reduces these contrasting representations of value to a single dimension, a common currency, in order to compare alternative choices.

Reversal learning as a measure of impulsive and compulsive behavior in addictions

BACKGROUND

Our ability to measure the cognitive components of complex decision-making across species has greatly facilitated our understanding of its neurobiological mechanisms. One task in particular, reversal learning, has proven valuable in assessing the inhibitory processes that are central to executive control. Reversal learning measures the ability to actively suppress reward-related responding and to disengage from ongoing behavior, phenomena that are biologically and descriptively related to impulsivity and compulsivity. Consequently, reversal learning could index vulnerability for disorders characterized by impulsivity such as proclivity for initial substance abuse as well as the compulsive aspects of dependence.

OBJECTIVE

Though we describe common variants and similar tasks, we pay particular attention to discrimination reversal learning, its supporting neural circuitry, neuropharmacology and genetic determinants. We also review the utility of this task in measuring impulsivity and compulsivity in addictions.

METHODS

We restrict our review to instrumental, reward-related reversal learning studies as they are most germane to addiction.

CONCLUSION

The research reviewed here suggests that discrimination reversal learning may be used as a diagnostic tool for investigating the neural mechanisms that mediate impulsive and compulsive aspects of pathological reward-seeking and -taking behaviors. Two interrelated mechanisms are posited for the neuroadaptations in addiction that often translate to poor reversal learning: frontocorticostriatal circuitry dysregulation and poor dopamine (D2 receptor) modulation of this circuitry. These data suggest new approaches to targeting inhibitory control mechanisms in addictions.

Considering anger from a cognitive neuroscience perspective

The goal of this paper is to consider anger from a cognitive neuroscience perspective. Five main claims are made: first, reactive aggression is the ultimate behavioral expression of anger and thus we can begin to understand anger by understanding reactive aggression. Second, neural systems implicated in reactive aggression (amygdala, hypothalamus, and periaqueductal gray; the basic threat system) are critically implicated in anger. Factors such as exposure to extreme threat that increase the responsiveness of these systems, should be (and are in the context of posttraumatic stress disorder), associated with increased anger. Third, regions of frontal cortex implicated in regulating the basic threat system, when dysfunctional (e.g., in the context of lesions) should be associated with increased anger. Fourth, frustration occurs when an individual continues to do an action in the expectation of a reward but does not actually receive that reward, and is associated with anger. Individuals who show impairment in the ability to alter behavioral responding when actions no longer receive their expected rewards should be (and are in the context of psychopathy) associated with increased anger. Fifth, someone not doing what another person wants them to do (particularly if this thwarts the person's goal) is frustrating and consequently anger inducing. The response to such a frustrating social event relies on the neural architecture implicated in changing behavioral responses in nonsocial frustrating situations. WIREs Cogn Sci 2012, 3:65-74. doi: 10.1002/wcs.154 This article is categorized under: Psychology > Brain Function and Dysfunction.

Orbitofrontal cortex and basolateral amygdala lesions result in suboptimal and dissociable reward choices on cue-guided effort in rats

The orbitofrontal cortex (OFC) and basolateral nucleus of the amygdala (BLA) are important neural regions in responding adaptively to changes in the incentive value of reward. Recent evidence suggests these structures may be differentially engaged in effort and cue-guided choice behavior. In 2 T-maze experiments, we examined the effects of bilateral lesions of either BLA or OFC on (1) effortful choices in which rats could climb a barrier for a high reward or select a low reward with no effort and (2) effortful choices when a visual cue signaled changes in reward magnitude. In both experiments, BLA rats displayed transient work aversion, choosing the effortless low reward option. OFC rats were work averse only in the no cue conditions, displaying a pattern of attenuated recovery from the cue conditions signaling reward unavailability in the effortful arm. Control measures rule out an inability to discriminate the cue in either lesion group.

Dissociable effects of subtotal lesions within the macaque orbital prefrontal cortex on reward-guided behavior

The macaque orbital prefrontal cortex (PFo) has been implicated in a wide range of reward-guided behaviors essential for efficient foraging. The PFo, however, is not a homogeneous structure. Two major subregions, distinct by their cytoarchitecture and connections to other brain structures, compose the PFo. One subregion encompasses Walker's areas 11 and 13 and the other centers on Walker's area 14. Although it has been suggested that these subregions play dissociable roles in reward-guided behavior, direct neuropsychological evidence for this hypothesis is limited. To explore the independent contributions of PFo subregions to behavior, we studied rhesus monkeys (Macaca mulatta) with restricted excitotoxic lesions targeting either Walker's areas 11/13 or area 14. The performance of these two groups was compared to that of a group of unoperated controls on a series of reward-based tasks that has been shown to be sensitive to lesions of the PFo as a whole (Walker's areas 11, 13, and 14). Lesions of areas 11/13, but not area 14, disrupted the rapid updating of object value during selective satiation. In contrast, lesions targeting area 14, but not areas 11/13, impaired the ability of monkeys to learn to stop responding to a previously rewarded object. Somewhat surprisingly, neither lesion disrupted performance on a serial object reversal learning task, although aspiration lesions of the entire PFo produce severe deficits on this task. Our data indicate that anatomically defined subregions within macaque PFo make dissociable contributions to reward-guided behavior.

Contribution of the amygdala, but not orbitofrontal or medial prefrontal cortices, to the expression of flavour preferences in marmoset monkeys

The development of food preferences contributes to a balanced diet, and involves both innate and learnt factors. By associating flavour cues with the reinforcing properties of the food (i.e. postingestive nutrient cues and innately preferred tastes, such as sweetness), animals acquire individual preferences. How the brain codes and guides selection when the subject has to choose between different palatable foods is little understood. To investigate this issue, we trained common marmoset monkeys (Callithrix jacchus) to respond to abstract visual patterns on a touch-sensitive computer screen to gain access to four different flavoured juices. After preferences were stable, animals received excitotoxic lesions of either the amygdala, the orbitofrontal cortex or the medial prefrontal cortex. Neither the orbitofrontal nor the medial prefrontal cortex lesions affected pre-surgery-expressed flavour preferences or the expression of preferences for novel flavours post-surgery. In contrast, amygdala lesions caused a shift in the preferences for juices expressed pre-surgery such that, post-surgery, juices were chosen according to their overall carbohydrate (simple sugars) content or 'sweetness'. Subsequent tests revealed that amygdala-lesioned animals only expressed juice preferences if they differed in 'sweetness'. Unlike controls, orbitofrontal cortex-lesioned and medial prefrontal cortex-lesioned animals, they were unable to display preferences between juices matched for 'sweetness' i.e. 5% sucrose solutions aromatised with different essential oils. The most parsimonious explanation is that the amygdala contributes to the expression of food preferences based on learnt cues but not those based on an innate preference for sweetness.

Updating existing emotional memories involves the frontopolar/orbito-frontal cortex in ways that acquiring new emotional memories does not

In life, we must often learn new associations to people, places, or things we already know. The current fMRI study investigated the neural mechanisms underlying emotional memory updating. Nineteen participants first viewed negative and neutral pictures and learned associations between those pictures and other neutral stimuli, such as neutral objects and encoding tasks. This initial learning phase was followed by a memory updating phase, during which participants learned picture-location associations for old pictures (i.e., pictures previously associated with other neutral stimuli) and new pictures (i.e., pictures not seen in the first phase). There was greater frontopolar/orbito-frontal (OFC) activity when people learned picture-location associations for old negative pictures than for new negative pictures, but frontopolar OFC activity did not significantly differ during learning locations of old versus new neutral pictures. In addition, frontopolar activity was more negatively correlated with the amygdala when participants learned picture-location associations for old negative pictures than for new negative or old neutral pictures. Past studies revealed that the frontopolar OFC allows for updating the affective values of stimuli in reversal learning or extinction of conditioning [e.g., Izquierdo, A., & Murray, E. A. Opposing effects of amygdala and orbital PFC lesions on the extinction of instrumental responding in macaque monkeys. European Journal of Neuroscience, 22, 2341-2346, 2005]; our findings suggest that it plays a more general role in updating associations to emotional stimuli.

Impaired safety signal learning may be a biomarker of PTSD

A dysregulated fear response is one of the hallmark clinical presentations of patients suffering from posttraumatic stress disorder (PTSD). These patients show over-generalization of fear and in tandem an inability to inhibit fear responses in the presence of safety. Here, we summarize our recent findings using a conditional discrimination paradigm, which assesses safety signal processing (AX+/BX-) in combat and civilian PTSD populations. Overall, PTSD subjects demonstrate a lack of safety signal learning and an inability to modulate the fear responses with safety cues. We then review studies of the neurobiology of fear expression and inhibition in humans and non-humans, in order to provide a background for preliminary studies using reverse translation procedures in which the same AX+/BX- paradigm was used in rhesus macaques. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Brain connectivity in listening to affective stimuli: a functional magnetic resonance imaging (fMRI) study and implications for psychotherapy

To investigate the functional connectivity among amygdala, insula, and auditory cortex during affective auditory stimulation and its relevance for psychotherapy, the authors recorded, using functional magnetic resonance imaging (fMRI), the blood oxygenation level-dependent (BOLD) responses of these brain regions in 20 healthy adults while listening to affective sounds (laughing and crying). Their connectivity was analyzed by time-series panel analysis. The authors found significant positive associations among brain regions, with time-lagged associations generally directed from the right to the left hemisphere. Associations between amygdalar and cortical regions, however, were negative; specifically, activations of the left auditory cortex preceded decreases of the right amygdala. This suggested that affect regulation using cognitive control may have been achieved through active inhibition of amygdalar structures by the cortex. The authors discuss the implications of the findings for the change mechanisms inherent in psychotherapy.

Amygdala-frontal connectivity during emotion regulation

Successful control of affect partly depends on the capacity to modulate negative emotional responses through the use of cognitive strategies (i.e., reappraisal). Recent studies suggest the involvement of frontal cortical regions in the modulation of amygdala reactivity and the mediation of effective emotion regulation. However, within-subject inter-regional connectivity between amygdala and prefrontal cortex in the context of affect regulation is unknown. Here, using psychophysiological interaction analyses of functional magnetic resonance imaging data, we show that activity in specific areas of the frontal cortex (dorsolateral, dorsal medial, anterior cingulate, orbital) covaries with amygdala activity and that this functional connectivity is dependent on the reappraisal task. Moreover, strength of amygdala coupling with orbitofrontal cortex and dorsal medial prefrontal cortex predicts the extent of attenuation of negative affect following reappraisal. These findings highlight the importance of functional connectivity within limbic-frontal circuitry during emotion regulation.

Inactivation of the central but not the basolateral nucleus of the amygdala disrupts learning in response to overexpectation of reward

The amygdala is critical for associating predictive cues with primary rewarding and aversive outcomes. This is particularly evident in tasks in which information about expected outcomes is required for normal responding. Here we used a pavlovian overexpectation task to test whether outcome signaling by amygdala might also be necessary for changing those representations in the face of unexpected outcomes. Rats were trained to associate several different cues with a food reward. After learning, two of the cues were presented together, in compound, followed by the same reward. Before each compound training session, rats received infusions of 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide or saline into either the basolateral (ABL) or central nucleus (CeN) of amygdala. We found that infusions into CeN abolished the normal decline in responding to the compounded cue in a later probe test, whereas infusions into ABL had no effect. These results are inconsistent with the proposal that signaling of information about expected outcomes by ABL contributes to learning, at least in this setting, and instead implicate the CeN in this process, perhaps attributable to the hypothesized involvement of this area in attention and variations in stimulus processing.

Interactions between orbital prefrontal cortex and amygdala: advanced cognition, learned responses and instinctive behaviors

Recent research indicates that the orbital prefrontal cortex (PFo) represents stimulus valuations and that the amygdala updates these valuations. An exploration of how PFo and the amygdala interact could improve the understanding of both. PFo and the amygdala function cooperatively when monkeys choose objects associated with recently revalued foods. In other tasks, they function in opposition. PFo uses positive feedback to promote learning in object-reward reversal tasks, and PFo also promotes extinction learning. Amygdala function interferes with both kinds of learning. The amygdala underlies fearful responses to a rubber snake from the first exposure on, but PFo is necessary only after the initial exposure. The amygdala mediates an arousal response in anticipation of rewards, whereas PFo sometimes suppresses such arousal. A role for PFo in advanced cognition, for the amygdala in instinctive behavior, and for cortex-subcortex interactions in prioritizing behaviors provides one account for these findings.

Emotion, cognition, and mental state representation in amygdala and prefrontal cortex

Neuroscientists have often described cognition and emotion as separable processes implemented by different regions of the brain, such as the amygdala for emotion and the prefrontal cortex for cognition. In this framework, functional interactions between the amygdala and prefrontal cortex mediate emotional influences on cognitive processes such as decision-making, as well as the cognitive regulation of emotion. However, neurons in these structures often have entangled representations, whereby single neurons encode multiple cognitive and emotional variables. Here we review studies using anatomical, lesion, and neurophysiological approaches to investigate the representation and utilization of cognitive and emotional parameters. We propose that these mental state parameters are inextricably linked and represented in dynamic neural networks composed of interconnected prefrontal and limbic brain structures. Future theoretical and experimental work is required to understand how these mental state representations form and how shifts between mental states occur, a critical feature of adaptive cognitive and emotional behavior.

Power spectrum scale invariance quantifies limbic dysregulation in trait anxious adults using fMRI: adapting methods optimized for characterizing autonomic dysregulation to neural dynamic time series

In a well-regulated control system, excitatory and inhibitory components work closely together with minimum lag; in response to inputs of finite duration, outputs should show rapid rise and, following the input's termination, immediate return to baseline. The efficiency of this response can be quantified using the power spectrum density's scaling parameter beta, a measure of self-similarity, applied to the first derivative of the raw signal. In this study, we adapted power spectrum density methods, previously used to quantify autonomic dysregulation (heart rate variability), to neural time series obtained via functional MRI. The negative feedback loop we investigated was the limbic system, using affect-valent faces as stimuli. We hypothesized that trait anxiety would be related to efficiency of regulation of limbic responses, as quantified by power-law scaling of fMRI time series. Our results supported this hypothesis, showing moderate to strong correlations of trait anxiety and beta (r=0.45-0.54) for the amygdala, orbitofrontal cortex, hippocampus, superior temporal gyrus, posterior insula, and anterior cingulate. Strong anticorrelations were also found between the amygdala's beta and wake heart rate variability (r=-0.61), suggesting a robust relationship between dysregulated limbic outputs and their autonomic consequences.

Orbitofrontal inactivation impairs reversal of Pavlovian learning by interfering with 'disinhibition' of responding for previously unrewarded cues

Orbitofrontal cortex (OFC) is critical for reversal learning. Reversal deficits are typically demonstrated in complex settings that combine Pavlovian and instrumental learning. Yet recent work has implicated the OFC specifically in behaviors guided by cues and the features of the specific outcomes they predict. To test whether the OFC is important for reversing such Pavlovian associations in the absence of confounding instrumental requirements, we trained rats on a simple Pavlovian task in which two auditory cues were presented, one paired with a food pellet reward and the other presented without reward. After learning, we reversed the cue-outcome associations. For half the rats, OFC was inactivated prior to each reversal session. Inactivation of OFC impaired the ability of the rats to reverse conditioned responding. This deficit reflected the inability of inactivated rats to develop normal responding for the previously unrewarded cue; inactivation of OFC had no impact on the ability of the rats to inhibit responding to the previously rewarded cue. These data show that OFC is critical to reversal of Pavlovian responding, and that the role of OFC in this behavior cannot be explained as a simple deficit in response inhibition. Furthermore, the contrast between the normal inhibition of responding, reported here, and impaired inhibition of responding during Pavlovian over-expectation, reported previously, suggests the novel hypothesis that OFC may be particularly critical for learning (or behavior) when it requires the subject to generate predictions about outcomes by bringing together or integrating disparate pieces of associative information.

Opposing effects of 5,7-DHT infusions into the orbitofrontal cortex and amygdala on flexible responding

Central serotonin is implicated in a variety of emotional and behavioral control processes. Serotonin depletion can lead to exaggerated aversive processing and deficient response inhibition, effects that have been linked to serotonin's actions in the amygdala and orbitofrontal cortex (OFC), respectively. However, a direct comparison of serotonin manipulations within the OFC and amygdala in the same experimental context has not been undertaken. This study compared the effects of infusing the serotonin neurotoxin, 5,7-dihydroxytryptamine into the OFC and amygdala of marmosets performing an appetitive test of response inhibition. Marmosets had to learn to inhibit a prepotent response tendency to choose a box containing high-incentive food and instead choose a box containing low-incentive food, to obtain reward. OFC infusions caused long-lasting reductions in serotonin tissue levels, as revealed at postmortem, and exaggerated prepotent responses. In contrast, the significantly reduced prepotent responses following amygdala infusions occurred at a time when serotonin tissue levels had undergone considerable recovery, but there remained residual reductions in extracellular serotonin, in vivo. These opposing behavioral effects of serotonin manipulations in the same experimental context may be understood in terms of the top-down regulatory control of the amygdala by the OFC.

Involvement of the lateral orbitofrontal cortex in drug context-induced reinstatement of cocaine-seeking behavior in rats

Orbitofrontal cortex (OFC) damage produces impaired decision-making, impulsivity and perseveration and potentially contributes to compulsive drug seeking in cocaine users. To further explore this phenomenon, we assessed the role of the lateral OFC (lOFC) in drug context-induced cocaine-seeking behavior in the reinstatement model of drug relapse. Rats were trained to lever press for intravenous cocaine infusions in a distinct environmental context (cocaine-paired context) followed by extinction training in a different context (extinction-paired context). Reinstatement of cocaine seeking (non-reinforced lever presses) was assessed in the cocaine context in the absence of response-contingent stimuli. In Experiment 1, we evaluated whether acute inhibition of lOFC output alters context-induced cocaine-seeking behavior by infusing the GABA(B + A) agonists (baclofen + muscimol) or vehicle into the lOFC immediately before exposure to the cocaine-paired context. In Experiments 2 and 3, we assessed how prolonged loss of lOFC output affects drug context-induced cocaine seeking by administering bilateral N-methyl-d-aspartic acid or sham lesions of the lOFC either before or after self-administration and extinction training. Remarkably, IOFC functional inactivation attenuated, post-training lesions failed to alter and pre-training lesions potentiated drug context-induced cocaine seeking without altering responding in the extinction context. These results suggest that neural activity in the lOFC promotes context-induced cocaine-seeking behavior. However, prolonged loss of lOFC output enhances the motivational salience of cocaine-paired contextual stimuli probably by eliciting compensatory neuroadaptations, with the effects of post-training lOFC lesions reflecting an intermediate state of compensatory neuroplasticity. Overall, these findings support the idea that OFC dysfunction may promote cue reactivity and enhance relapse propensity in cocaine users.

Structure-function relationships in the processing of regret in the orbitofrontal cortex

The influence of counterfactual thinking and regret on choice behavior has been widely acknowledged in economic science (Bell in Oper Res 30:961-981, 1982; Kahneman and Tversky in Judgment under uncertainty: heuristics and biases. Cambridge University Press, Cambridge, pp 201-210, 1982; Loomes and Sugden in Econ J 92:805-824, 1982). Neuroimaging studies have only recently begun to explore the neural correlates of this psychological factor and orbitofrontal cortex (OFC) activity was observed in several of them depending of the exact characteristics of the employed paradigm. This selective OFC involvement and, moreover, a consistently found dissociation of medial and lateral OFC activity clusters allow inferences to the function of this structure in counterfactual thinking and regret. Vice versa, the differential contribution of OFC subregions to these processes also adds evidence to the current debate on the function of this cortical structure in decision-making that attracted increasing attention in recent years.

The orbitofrontal cortex and ventral tegmental area are necessary for learning from unexpected outcomes

Humans and other animals change their behavior in response to unexpected outcomes. The orbitofrontal cortex (OFC) is implicated in such adaptive responding, based on evidence from reversal tasks. Yet these tasks confound using information about expected outcomes with learning when those expectations are violated. OFC is critical for the former function; here we show it is also critical for the latter. In a Pavlovian overexpectation task, inactivation of OFC prevented learning driven by unexpected outcomes, even when performance was assessed later. We propose this reflects a critical contribution of outcome signaling by OFC to encoding of reward prediction errors elsewhere. In accord with this proposal, we report that signaling of reward predictions by OFC neurons was related to signaling of prediction errors by dopamine neurons in ventral tegmental area (VTA). Furthermore, bilateral inactivation of VTA or contralateral inactivation of VTA and OFC disrupted learning driven by unexpected outcomes.