Different types of fear-conditioned behaviour mediated by separate nuclei within amygdala

Fatal attraction: ventral striatum predicts costly choice errors in humans

Animals approach rewards and cues associated with reward, even when this behavior is irrelevant or detrimental to the attainment of these rewards. Motivated by these findings we study the biology of financially-costly approach behavior in humans. Our subjects passively learned to predict the occurrence of erotic rewards. We show that neuronal responses in ventral striatum during this Pavlovian learning task stably predict an individual's general tendency towards financially-costly approach behavior in an active choice task several months later. Our data suggest that approach behavior may prevent some individuals from acting in their own interests.

Amygdalostriatal projections in the neurocircuitry for motivation: a neuroanatomical thread through the career of Ann Kelley

In MacLean's triune brain, the amygdala putatively subserves motivated behavior by modulating the "reptilian" basal ganglia. Accordingly, Ann Kelley, with Domesick and Nauta, influentially showed that amygdalostriatal projections are much more extensive than were appreciated. They highlighted that amygdalar projections to the rostral ventromedial striatum converged with projections from the ventral tegmental area and cingulate cortex, forming a "limbic striatum". Caudal of the anterior commissure, the entire striatum receives afferents from deep basal nuclei of the amygdala. Orthologous topographic projections subsequently were observed in fish, amphibians, and reptiles. Subsequent functional studies linked acquired value to action via this neuroanatomical substrate. From Dr. Kelley's work evolved insights into components of the distributed, interconnected network that subserves motivated behavior, including the nucleus accumbens shell and core and the striatal-like extended amygdala macrostructure. These heuristic frameworks provide a neuroanatomical basis for adaptively translating motivation into behavior. The ancient amygdala-to-striatum pathways remain a current functional thread not only for stimulus-response valuation, but also for the psychopathological plasticity that underlies addiction-related memory, craving and relapse.

Conditioned flavor avoidance and conditioned gaping: rat models of conditioned nausea

Although rats are incapable of vomiting, they demonstrate profound avoidance of a flavor previously paired with an emetic drug. They also display conditioned gaping reactions during re-exposure to the flavor. This robust learning occurs in a single trial and with long delays (hours) between consumption of a novel flavor and the emetic treatment. However, conditioned flavor avoidance learning is not a selective measure of the emetic properties of drugs, because non-emetic treatments (even highly rewarding treatments) produce conditioned avoidance, and anti-emetic treatments are generally ineffective in suppressing conditioned avoidance produced by an emetic drug. On the other hand, conditioned gaping reactions are consistently produced by emetic drugs and are prevented by anti-emetic drugs, indicating that they may be a more selective measure of conditioned malaise in rats. Here we review the literature on the use of conditioned flavor avoidance and conditioned gaping reactions as rat measures of conditioned nausea, as well as the neuropharmacology and neuroanatomy of conditioned gaping reactions in rats.

Differential roles of the prefrontal cortical subregions and basolateral amygdala in compulsive cocaine seeking and relapse after voluntary abstinence in rats

Compulsive drug use and a persistent vulnerability to relapse are key features of addiction. Imaging studies have suggested that these features may result from deficits in prefrontal cortical structure and function, and thereby impaired top-down inhibitory control over limbic-striatal mechanisms of drug-seeking behaviour. We tested the hypothesis that selective damage to distinct subregions of the prefrontal cortex, or to the amygdala, after a short history of cocaine taking would: (i) result in compulsive cocaine seeking at a time when it would not usually be displayed; or (ii) facilitate relapse to drug seeking after abstinence. Rats with selective, bilateral excitotoxic lesions of the basolateral amygdala or anterior cingulate, prelimbic, infralimbic, orbitofrontal or anterior insular cortices were trained to self-administer cocaine under a seeking-taking chained schedule. Intermittent mild footshock punishment of the cocaine-seeking response was then introduced. No prefrontal cortical lesion affected the ability of rats to withhold their seeking responses. However, rats with lesions to the basolateral amygdala increased their cocaine-seeking responses under punishment and were impaired in their acquisition of conditioned fear. Following a 7-day abstinence period, rats were re-exposed to the drug-seeking environment for assessment of relapse in the absence of punishment or cocaine. Rats with prelimbic cortex lesions showed decreased seeking responses during relapse, whereas those with anterior insular cortex lesions showed an increase. Combined, these results show that acute impairment of prefrontal cortical function does not result in compulsive cocaine seeking after a short history of self-administering cocaine, but further implicates subregions of the prefrontal cortex in relapse.

The amygdala: an agent of change in adolescent neural networks

This article is part of a Special Issue "Puberty and Adolescence". A unique component of adolescent development is the need to master new developmental tasks in which peer interactions become primary (for the purposes of becoming autonomous from parents, forming intimate friendships, and romantic/sexual partnerships). Previously, it has been suggested that the ability to master these tasks requires an important re-organization in the relation between perceptual, motivational, affective, and cognitive systems in a very general and broad way that is fundamentally influenced by the infusion of sex hormones during pubertal development (Scherf et al., 2012). Herein, we extend this argument to suggest that the amygdala, which is vastly connected with cortical and subcortical regions and contains sex hormone receptors, may lie at the heart of this re-organization. We propose that during adolescent development there is a shift in the attribution of relevance to existing stimuli and contexts that is mediated by the amygdala (e.g., heightened relevance of peer faces, reduced relevance of physical distance from parents). As a result, amygdala inputs to existing stable neural networks are re-weighted (increased or decreased), which destabilizes the functional interactions among regions within these networks and allows for a critical restructuring of the network functional organization. This process of network re-organization enables processing of qualitatively new kinds of social information and the emergence of novel behaviors that support mastery of adolescent-specific developmental tasks.

Human amygdala volume is predicted by common DNA variation in the stathmin and serotonin transporter genes

Despite the relevance of changes in amygdala volume to psychiatric illnesses and its heritability in both health and disease, the influence of common genetic variation on amygdala morphology remains largely unexplored. In the present study, we investigated the influence of a number of novel genetic variants on amygdala volume in 139 neurologically healthy individuals of European descent. Amygdala volume was significantly associated with allelic variation in the stathmin (STMN1) and serotonin transporter (SLC6A4) genes, which have been linked to healthy and disordered affective processing. These results were replicated across both manual and automated methods of amygdala parcellation, although manual tracing showed stronger effects, providing a cautionary note to studies relying on automated parcellation methods. Future studies will need to determine whether amygdala volume mediates the impact of stathmin and serotonin transporter gene variants on normal and dysfunctional emotion processing.

The Contribution of the Amygdala to Aversive and Appetitive Pavlovian Processes

Pavlovian cues predict the occurrence of motivationally salient outcomes, thus serving as an important trigger of approach and avoidance behavior. The amygdala is a key substrate of Pavlovian conditioning, and the nature of its contribution varies by the motivational valence of unconditioned stimuli. The literature on aversive Pavlovian learning supports a serial-processing model of amygdalar function, while appetitive studies suggest that Pavlovian associations are processed through parallel circuits in the amygdala. It is proposed that serial and parallel forms of information processing can be attributed to differential recruitment of amygdalar nuclei, with emphasis placed on the lateral amygdala.

Anterior olfactory organ removal produces anxiety-like behavior and increases spontaneous neuronal firing rate in basal amygdala

Some chemical cues may produce signs of anxiety and fear mediated by amygdala nuclei, but unknown is the role of two anterior olfactory epithelial organs, the septal and vomeronasal organs (SO-VNOs). The effects of SO-VNO removal were explored in different groups of Wistar rats using two complementary approaches: (i) the assessment of neuronal firing rate in basal and medial amygdala nuclei and (ii) behavioral testing. Fourteen days after SO-VNO removal, spontaneous activity in basal and medial amygdala nuclei in one group was determined using single-unit extracellular recordings. A separate group of rats was tested in the elevated plus maze, social interaction test, and open field test. Compared with sham-operated and intact control rats, SO-VNO removal produced a higher neuronal firing rate in the basal amygdala but not medial amygdala. In the behavioral tests, SO-VNO removal increased signs of anxiety in the elevated plus maze, did not alter locomotion, and increased self-directed behavior, reflecting anxiety-like behavior. Histological analysis showed neuronal destruction in the accessory olfactory bulb but not anterior olfactory nucleus in the SO-VNO group. The present results suggest the participation of SO-VNO/accessory olfactory bulb/basal amygdala relationships in the regulation of anxiety through a process of disinhibition.

The role of the dorsoanterior striatum in implicit motivation: the case of the need for power

Implicit motives like the need for power (nPower) scale affective responses to need-specific rewards or punishments and thereby influence activity in motivational-brain structures. In this paper, we review evidence specifically supporting a role of the striatum in nPower. Individual differences in nPower predict (1) enhanced implicit learning accuracy, but not speed, on serial-response tasks that are reinforced by power-related incentives (e.g., winning or losing a contest; dominant or submissive emotional expressions) in behavioral studies and (2) activation of the anterior caudate in response to dominant emotional expressions in brain imaging research. We interpret these findings on the basis of Hikosaka et al.'s (2002a) model of central mechanisms of motor skill learning. The model assigns a critical role to the dorsoanterior striatum in dopamine-driven learning of spatial stimulus sequences. Based on this model, we suggest that the dorsoanterior striatum is the locus of nPower-dependent reinforcement. However, given the centrality of this structure in a wide range of motivational pursuits, we also propose that activity in the dorsoanterior striatum may not only reflect individual differences in nPower, but also in other implicit motives, like the need for achievement or the need for affiliation, provided that the proper incentives for these motives are present during reinforcement learning. We discuss evidence in support of such a general role of the dorsoanterior striatum in implicit motivation.

Forebrain networks and the control of feeding by environmental learned cues

The motivation to eat is driven by a complex sum of physiological and non-physiological influences computed by the brain. Physiological signals that inform the brain about energy and nutrient needs are the primary drivers, but environmental signals unrelated to energy balance also control appetite and eating. The two components could act in concert to support the homeostatic regulation of food intake. Often, however, environmental influences rival physiological control and stimulate eating irrespective of satiety, or inhibit eating irrespective of hunger. If persistent, such maladaptive challenges to the physiological system could lead to dysregulated eating and ultimately to eating disorders. Nevertheless, the brain mechanisms underlying environmental contribution in the control of food intake are poorly understood. This paper provides an overview in recent advances in deciphering the critical brain systems using rodent models for environmental control by learned cues. These models use associative learning to compete with the physiological control, and in one preparation food cues stimulate a meal despite satiety, while in another preparation fear cues stop a meal despite hunger. Thus far, four forebrain regions have been identified as part of the essential cue induced feeding circuitry. These are telencephalic areas critical for associative learning, memory encoding, and decision making, the amygdala, hippocampus and prefrontal cortex and the lateral hypothalamus, which functions to integrate feeding, reward, and motivation. This circuitry also engages two orexigenic peptides, ghrelin and orexin. A parallel amygdalar circuitry supports fear cue cessation of feeding. These findings illuminate the brain mechanisms underlying environmental control of food intake and might be also relevant to aspects of human appetite and maladaptive overeating and undereating.

Double dissociation of the requirement for GluN2B- and GluN2A-containing NMDA receptors in the destabilization and restabilization of a reconsolidating memory

Signaling at NMDA receptors (NMDARs) is known to be important for memory reconsolidation, but while most studies show that NMDAR antagonists prevent memory restabilization and produce amnesia, others have shown that GluN2B-selective NMDAR antagonists prevent memory destabilization, protecting the memory. These apparently paradoxical, conflicting data provide an opportunity to define more precisely the requirement for different NMDAR subtypes in the mechanisms underlying memory reconsolidation and to further understand the contribution of glutamatergic signaling to this process. Here, using rats with fully consolidated pavlovian auditory fear memories, we demonstrate a double dissociation in the requirement for GluN2B-containing and GluN2A-containing NMDARs within the basolateral amygdala in the memory destabilization and restabilization processes, respectively. We further show a double dissociation in the mechanisms underlying memory retrieval and memory destabilization, since AMPAR antagonism prevented memory retrieval while still allowing the destabilization process to occur. These data demonstrate that glutamatergic signaling mechanisms within the basolateral amygdala differentially and dissociably mediate the retrieval, destabilization, and restabilization of previously consolidated fear memories.

2-Heptanone increases the firing rate of the basal amygdala: role of anterior olfactory epithelial organs

Wistar rats subjected to physical stress release a urine alarm pheromone (2-heptanone) that produces signs of anxiety and despair in receptor rats not subjected to physical stress. However, unknown are the effects of 2-heptanone on the firing rate of the basal amygdala, a structure that participates in the expression of fear, and the participation of anterior olfactory epithelial organs, namely the septal organ and vomeronasal organ (SO-VNO). We explored the effects of 2-heptanone applied near the nostrils on single-unit extracellular recordings from the basal amygdala in a sham-operated group and rats that underwent removal of the SO-VNO. The firing rate of basal amygdala neurons in the SO-VNO removal group was significantly higher than in the sham-operated group. In both groups, recordings were classified according to the responses to 2-heptanone (i.e., increased firing rate, decreased firing rate, and no response). SO-VNO removal was associated with an increased firing rate in the three types of neurons. A similar number of neurons increased their firing rate during and after 2-heptanone stimulation in both groups, but such an increase in firing rate was longer in the group of rats subjected to SO-VNO removal. The results indicate that the SO-VNO is not essential for the effect of 2-heptanone on the firing rate of basal amygdala neurons. SO-VNO ablation did not block but rather accentuated the response of amygdala neurons to 2-heptanone.

Generous economic investments after basolateral amygdala damage

Contemporary economic models hold that instrumental and impulsive behaviors underlie human social decision making. The amygdala is assumed to be involved in social-economic behavior, but its role in human behavior is poorly understood. Rodent research suggests that the basolateral amygdala (BLA) subserves instrumental behaviors and regulates the central-medial amygdala, which subserves impulsive behaviors. The human amygdala, however, typically is investigated as a single unit. If these rodent data could be translated to humans, selective dysfunction of the human BLA might constrain instrumental social-economic decisions and result in more impulsive social-economic choice behavior. Here we show that humans with selective BLA damage and a functional central-medial amygdala invest nearly 100% more money in unfamiliar others in a trust game than do healthy controls. We furthermore show that this generosity is not caused by risk-taking deviations in nonsocial contexts. Moreover, these BLA-damaged subjects do not expect higher returns or perceive people as more trustworthy, implying that their generous investments are not instrumental in nature. These findings suggest that the human BLA is essential for instrumental behaviors in social-economic interactions.

The biology of fear

Each of us has felt afraid, and we can all recognize fear in many animal species. Yet there is no consensus in the scientific study of fear. Some argue that 'fear' is a psychological construct rather than something discoverable through scientific investigation. Others argue that the term 'fear' cannot properly be applied to animals because we cannot know whether they feel afraid. Studies in rodents show that there are highly specific brain circuits for fear, whereas findings from human neuroimaging seem to make the opposite claim. Here, I review the field and urge three approaches that could reconcile the debates. For one, we need a broadly comparative approach that would identify core components of fear conserved across phylogeny. This also pushes us towards the second point of emphasis: an ecological theory of fear that is essentially functional. Finally, we should aim even to incorporate the conscious experience of being afraid, reinvigorating the study of feelings across species.

Long-term treatment with standardized extract of Ginkgo biloba L. enhances the conditioned suppression of licking in rats by the modulation of neuronal and glial cell function in the dorsal hippocampus and central amygdala

Our group previously demonstrated that short-term treatment with a standardized extract of Ginkgo biloba (EGb) changed fear-conditioned memory by modulating gene expression in the hippocampus, amygdaloid complex and prefrontal cortex. Although there are few controlled studies that support the long-term use of EGb for the prevention and/or treatment of memory impairment, the chronic use of Ginkgo is common. This study evaluated the effects of chronic treatment with EGb on the conditioned emotional response, assessed by the suppression of ongoing behavior and in the modulation of gene and protein expression. Male adult Wistar rats were treated over 28days and assigned to five groups (n=10) as follows: positive control (4mgkg(-1) Diazepam), negative control (12% Tween 80), EGb groups (0.5 and 1.0gkg(-1)) and the naïve group. The suppression of the licking response was calculated for each rat in six trials. Our results provide further evidence for the efficacy of EGb on memory. For the first time, we show that long-term treatment with the highest dose of EGb improves the fear memory and suggests that increased cAMP-responsive element-binding protein (CREB)-1 and glial fibrillary acidic protein (GFAP) mRNA and protein (P<0.001) in the dorsal hippocampus and amygdaloid complex and reduced growth and plasticity-associated protein 43 (GAP-43) (P<0.01) in the hippocampus are involved in this process. The fear memory/treatment-dependent changes observed in our study suggest that EGb might be effective for memory enhancement through its effect on the dorsal hippocampus and amygdaloid complex.

The biology of fear- and anxiety-related behaviors

Anxiety is a psychological, physiological, and behavioral state induced in animals and humans by a threat to well-being or survival, either actual or potential. It is characterized by increased arousal, expectancy, autonomic and neuroendocrine activation, and specific behavior patterns. The function of these changes is to facilitate coping with an adverse or unexpected situation. Pathological anxiety interferes with the ability to cope successfully with life challenges. Vulnerability to psychopathology appears to be a consequence of predisposing factors (or traits), which result from numerous gene-environment interactions during development (particularly during the perinatal period) and experience (life events), in this review, the biology of fear and anxiety will be examined from systemic (brain-behavior relationships, neuronal circuitry, and functional neuroanatomy) and cellular/molecular (neurotransmitters, hormones, and other biochemical factors) points of view, with particular reference to animal models. These models have been instrumental in establishing the biological correlates of fear and anxiety, although the recent development of noninvasive investigation methods in humans, such as the various neuroimaging techniques, certainly opens new avenues of research in this field. Our current knowledge of the biological bases of fear and anxiety is already impressive, and further progress toward models or theories integrating contributions from the medical, biological, and psychological sciences can be expected.

Serotonin modulates the effects of Pavlovian aversive predictions on response vigor

Updated theoretical accounts of the role of serotonin (5-HT) in motivation propose that 5-HT operates at the intersection of aversion and inhibition, promoting withdrawal in the face of aversive predictions. However, the specific cognitive mechanisms through which 5-HT modulates withdrawal behavior remain poorly understood. Behavioral inhibition in response to punishments reflects at least two concurrent processes: instrumental aversive predictions linking stimuli, responses, and punishments, and Pavlovian aversive predictions linking stimuli and punishments irrespective of response. In the current study, we examined to what extent 5-HT modulates the impact of instrumental vs Pavlovian aversive predictions on behavioral inhibition. We used acute tryptophan depletion to lower central 5-HT levels in healthy volunteers, and observed behavior in a novel task designed to measure the influence of Pavlovian and instrumental aversive predictions on choice (response bias) and response vigor (response latencies). After placebo treatment, participants were biased against responding on the button that led to punishment, and they were slower to respond in a punished context, relative to a non-punished context. Specifically, participants slowed their responses in the presence of stimuli predictive of punishments. Tryptophan depletion removed the bias against responding on the punished button, and abolished slowing in the presence of punished stimuli, irrespective of response. We suggest that this set of results can be explained by a role for 5-HT in Pavlovian aversive predictions. These findings suggest additional specificity for the influence of 5-HT on aversively motivated behavioral inhibition and extend recent models of the role of 5-HT in aversive predictions.

Within-event learning in rats with lesions of the basolateral amygdala

Rats with neurotoxic lesions of the basolateral amygdala were trained in procedures designed to assess the formation of within-event, taste-odor associations. In Experiments 1 and 2 the animals were given initial exposure to a taste-odor compound; the value of the taste was then modified, and the consequent change in responding to the odor was taken to indicate that an odor-taste association had been formed. In Experiment 1 the value of the taste (saline) was enhanced by means of salt-depletion procedure; in Experiment 2 the taste was devalued by aversive conditioning. In neither procedure did lesioned animals differ from sham-operated controls. Experiment 3 confirmed, however, that taste-potentiation of odor aversion learning (an effect thought to depend on the formation of a taste-odor association) is abolished by the lesion. Implications for the view that the amygdala is necessary for sensory-sensory associations between events in different modalities are considered.

The tyrosine phosphatase STEP constrains amygdala-dependent memory formation and neuroplasticity

STriatal-Enriched protein tyrosine Phosphatase (STEP; PTPN5) is expressed in brain regions displaying adult neuroplasticity. STEP modulates neurotransmission by dephosphorylating regulatory tyrosine residues on its substrates. In this way, STEP inactivates extracellular-signal-regulated kinase 1/2 (ERK1/2), limiting the duration and spatial distribution of ERK signaling. Two additional substrates, the tyrosine kinase Fyn and the NR2B subunit of the N-methyl-d-aspartic acid receptor, link STEP to glutamate receptor internalization in the synapse. Thus, STEP may act through parallel pathways to oppose the development of experience-dependent synaptic plasticity. We examined the hypothesis that the absence of STEP facilitates amygdala-dependent behavioral and synaptic plasticity (i.e., fear conditioning and long-term potentiation) using STEP-deficient mice (STEP KO). These mice show no detectable expression of STEP in the brain along with increases in Tyr phosphorylation of STEP substrates. Here we demonstrate that STEP KO mice also display augmented fear conditioning as measured by an enhancement in conditioned suppression of instrumental response when a fear-associated conditioned stimulus was presented. Deletion of STEP also increases long-term potentiation and ERK phosphorylation in the lateral amygdala. The current experiments demonstrate that deletion of STEP can enhance experience-induced neuroplasticity and memory formation and identifies STEP as a target for pharmacological treatment aimed at improving the formation of long-term memories.

An investigation of the structural, connectional, and functional subspecialization in the human amygdala

Although the amygdala complex is a brain area critical for human behavior, knowledge of its subspecialization is primarily derived from experiments in animals. We here employed methods for large‐scale data mining to perform a connectivity‐derived parcellation of the human amygdala based on whole‐brain coactivation patterns computed for each seed voxel. Voxels within the histologically defined human amygdala were clustered into distinct groups based on their brain‐wide coactivation maps. Using this approach, connectivity‐based parcellation divided the amygdala into three distinct clusters that are highly consistent with earlier microstructural distinctions. Meta‐analytic connectivity modelling then revealed the derived clusters' brain‐wide connectivity patterns, while meta‐data profiling allowed their functional characterization. These analyses revealed that the amygdala's laterobasal nuclei group was associated with coordinating high‐level sensory input, whereas its centromedial nuclei group was linked to mediating attentional, vegetative, and motor responses. The often‐neglected superficial nuclei group emerged as particularly sensitive to olfactory and probably social information processing. The results of this model‐free approach support the concordance of structural, connectional, and functional organization in the human amygdala and point to the importance of acknowledging the heterogeneity of this region in neuroimaging research. Hum Brain Mapp 34:3247–3266, 2013. © 2012 Wiley Periodicals, Inc.

Stress Transiently Affects Pavlovian-to-Instrumental Transfer

Stress has a strong impact in the brain, impairing decision-making processes as a result of changes in circuits involving the prefrontal and orbitofrontal cortices and the striatum. Given that these same circuits are key for action control and outcome encoding, we hypothesized that adaptive responses to which these are essential functions, could also be targeted by stress. To test this hypothesis we herein assessed the impact of chronic stress in a Pavlovian-to-instrumental transfer (PIT) paradigm, a model of an adaptive response in which a previously conditioned cue biases an instrumental goal-directed action. Data reveals that rats submitted to chronic unpredictable stress did not display deficits in pavlovian conditioning nor on the learning of the instrumental task, but were impaired in PIT; importantly, after a stress-free period the PIT deficits were no longer observed. These results are relevant to understand how stress biases multiple incentive processes that contribute to instrumental performance.

Differential roles of the dorsolateral and midlateral striatum in punished cocaine seeking

Continued instrumental drug seeking despite contingent punishment is a core phenotype of drug addiction. Although the neuroanatomical basis of punished drug seeking is unclear, we hypothesize that the sensorimotor striatum, a structure that mediates habitual drug seeking, also mediates punished cocaine seeking. Forelimb sensorimotor projections into the striatum of the rat extend from the dorsolateral to midlateral striatum. Here, we selectively inactivated the dorsolateral and midlateral striatum in rats responding for cocaine in a seeking-taking task. We inactivated both regions after the acquisition of cocaine seeking, after extended cocaine self-administration and finally after the introduction of intermittent, seeking-contingent foot shock. The results show that inactivation of the dorsolateral striatum selectively disrupted punished drug seeking but did not affect unpunished drug seeking, even after extended training. Inactivation of the midlateral striatum, on the other hand, disrupted drug seeking at all stages of training. The effect of inactivating the dorsolateral striatum under punishment conditions was present before delivery of the first shock in the session, and responding reverted to baseline the next day. Thus, inactivation of the dorsolateral striatum seems to enhance the influence of recalled threat of negative consequences of cocaine seeking. The proportional reduction in responding after inactivation of the dorsolateral striatum did not vary with the individual level of compulsivity. Together, these results suggest a novel differentiation of function in the sensorimotor striatum, where the dorsolateral striatum selectively mediates the rigidity of responding after overtraining, while the midlateral striatum mediates responding itself at all stages of training.

Which cue to 'want'? Opioid stimulation of central amygdala makes goal-trackers show stronger goal-tracking, just as sign-trackers show stronger sign-tracking

Pavlovian cues that have been paired with reward can gain incentive salience. Drug addicts find drug cues motivationally attractive and binge eaters are attracted by food cues. But the level of incentive salience elicited by a cue re-encounter still varies across time and brain states. In an animal model, cues become attractive and 'wanted' in an 'autoshaping' paradigm, where different targets of incentive salience emerge for different individuals. Some individuals (sign-trackers) find a predictive discrete cue attractive while others find a reward contiguous goal cue more attractive (location where reward arrives: goal-trackers). Here we assessed whether central amygdala mu opioid receptor stimulation enhances the phasic incentive salience of the goal-cue for goal-trackers during moments of predictive cue presence (expressed in both approach and consummatory behaviors to goal cue), just as it enhances the attractiveness of the predictive cue target for sign-trackers. Using detailed video analysis we measured the approaches, nibbles, sniffs, and bites directed at their preferred target for both sign-trackers and goal-trackers. We report that DAMGO microinjections in central amygdala made goal-trackers, like sign-trackers, show phasic increases in appetitive nibbles and sniffs directed at the goal-cue expressed selectively whenever the predictive cue was present. This indicates enhancement of incentive salience attributed by both goal trackers and sign-trackers, but attributed in different directions: each to their own target cue. For both phenotypes, amygdala opioid stimulation makes the individual's prepotent cue into a stronger motivational magnet at phasic moments triggered by a CS that predicts the reward UCS.

Hypervigilance for fear after basolateral amygdala damage in humans

Recent rodent research has shown that the basolateral amygdala (BLA) inhibits unconditioned, or innate, fear. It is, however, unknown whether the BLA acts in similar ways in humans. In a group of five subjects with a rare genetic syndrome, that is, Urbach-Wiethe disease (UWD), we used a combination of structural and functional neuroimaging, and established focal, bilateral BLA damage, while other amygdala sub-regions are functionally intact. We tested the translational hypothesis that these BLA-damaged UWD-subjects are hypervigilant to facial expressions of fear, which are prototypical innate threat cues in humans. Our data indeed repeatedly confirm fear hypervigilance in these UWD subjects. They show hypervigilant responses to unconsciously presented fearful faces in a modified Stroop task. They attend longer to the eyes of dynamically displayed fearful faces in an eye-tracked emotion recognition task, and in that task recognize facial fear significantly better than control subjects. These findings provide the first direct evidence in humans in support of an inhibitory function of the BLA on the brain's threat vigilance system, which has important implications for the understanding of the amygdala's role in the disorders of fear and anxiety.

Orexin 1 receptors are a novel target to modulate panic responses and the panic brain network

BACKGROUND

Although the hypothalamic orexin system is known to regulate appetitive behaviors and promote wakefulness and arousal (Sakurai, 2007 [56]), this system may also be important in adaptive and pathological anxiety/stress responses (Suzuki et al., 2005 [4]). In a recent study, we demonstrated that CSF orexin levels were significantly higher in patients experiencing panic attacks compared to non-panicking depressed subjects (Johnson et al., 2010 [9]). Furthermore, genetically silencing orexin synthesis or blocking orexin 1 receptors attenuated lactate-induced panic in an animal model of panic disorder. Therefore, in the present study, we tested if orexin (ORX) modulates panic responses and brain pathways activated by two different panicogenic drugs.

METHODS

We conducted a series of pharmacological, behavioral, physiological and immunohistochemical experiments to study the modulation by the orexinergic inputs of anxiety behaviors, autonomic responses, and activation of brain pathways elicited by systemic injections of anxiogenic/panicogenic drugs in rats.

RESULTS

We show that systemic injections of two different anxiogenic/panicogenic drugs (FG-7142, an inverse agonist at the benzodiazepine site of the GABA(A) receptor, and caffeine, a nonselective competitive adenosine receptor antagonist) increased c-Fos induction in a specific subset of orexin neurons located in the dorsomedial/perifornical (DMH/PeF) but not the lateral hypothalamus. Pretreating rats with an orexin 1 receptor antagonist attenuated the FG-7142-induced anxiety-like behaviors, increased heart rate, and neuronal activation in key panic pathways, including subregions of the central nucleus of the amygdala, bed nucleus of the stria terminalis, periaqueductal gray and in the rostroventrolateral medulla.

CONCLUSION

Overall, the data here suggest that the ORX neurons in the DMH/PeF region are critical to eliciting coordinated panic responses and that ORX1 receptor antagonists constitute a potential novel treatment strategy for panic and related anxiety disorders. The neural pathways through which ORX1 receptor antagonists attenuate panic responses involve the extended amygdala, periaqueductal gray, and medullary autonomic centers.

Role of amygdala central nucleus in aversive learning produced by shock or by unexpected omission of food

Many psychological learning theories have noted commonalities between aversive states produced by presentation of negative reinforcers, such as electric shock, and the omission of expected positive reinforcers, such as food. Here, three groups of rats received training with one auditory cue paired with shock and another with the omission of expected food, a shock-paired cue and a food-omission control cue, or a food-omission cue and a shock control cue. Food-omission cues were established by contrast with food delivery; after extensive light-food pairings, the light was followed by the food-omission cue instead of food. Aversiveness of the food-omission cue was assessed with a conditioned punishment procedure, in which presentation of that cue was made contingent on performance of one previously trained instrumental response, whereas a second response had no consequences. We found that rats with lesions of amygdala central nucleus (CeA) showed impaired acquisition of freezing to the cue paired with shock and no evidence for acquisition of aversive properties by the cue that accompanied the omission of expected food. Furthermore, analyses of Arc and Homer1a mRNAs after rats were exposed to a two-epoch test procedure that allowed assessment of gene expression produced by two different test stimuli showed that both food-omission and shock-paired cues generated more neuronal activity in CeA than appropriate control cues. However, the number of neurons that were activated by both shock and food-omission cues was not significantly greater than expected by chance. Thus, under these test conditions, different subsets of CeA neurons represented these two aversive states.

Distorted expectancy coding in problem gambling: is the addictive in the anticipation?

BACKGROUND

Pathologic gamblers are known to have abnormal neural responses associated with experiencing monetary wins and losses. However, neural responsiveness during reward and loss expectations in pathologic gamblers has not yet been investigated.

METHODS

We used a functional magnetic resonance imaging paradigm that allowed us to investigate the dissociable reward- and loss-related expectancies with various probabilities of winning or losing different amounts of money in 15 patients with problem gambling (PRGs) and 16 healthy control subjects (HCs).

RESULTS

Compared with HCs, PRGs showed stronger activation in the bilateral ventral striatum to 5 euro than to 1 euro trials. PRGs also showed more activation of the bilateral ventral striatum and left orbitofrontal cortex associated with gain-related expected value than HCs. In addition, regression analyses indicated a highly significant negative correlation between gambling severity scores and right amygdala activation associated with gain-related expected value coding. There were no group differences in brain activation for loss-related expected value.

CONCLUSIONS

PRGs show higher activity in the reward system during reward expectation than HCs, whereas we observed no difference between PRGs and HC in the loss value system. Furthermore, the negative relation between gambling severity and amygdala activation in gain expected value coding suggests that more severe PRGs are less likely to be risk aversive during gambling. Our study provides evidence that PRGs are characterized by abnormally increased reward expectancy coding, which may render them overoptimistic with regard to gambling outcomes.

The role of the lateral amygdala in the retrieval and maintenance of fear-memories formed by repeated probabilistic reinforcement

The lateral nucleus of the amygdala (LA) is a key element in the neural circuit subserving Pavlovian fear-conditioning, an animal model of fear and anxiety. Most studies have focused on the role of the LA in fear acquisition and extinction, i.e., how neural plasticity results from changing contingencies between a neutral conditioned stimulus (CS) (e.g., a tone) and an aversive unconditioned stimulus (US) (e.g., a shock). However, outside of the lab, fear-memories are often the result of repeated and unpredictable experiences. Examples include domestic violence, child abuse or combat. To better understand the role of the LA in the expression of fear resulting from repeated and uncertain reinforcement, rats experienced a 30% partial reinforcement (PR) fear-conditioning schedule four days a week for four weeks. Rats reached asymptotic levels of conditioned-fear expression after the first week. We then manipulated LA activity with drug (or vehicle) (VEH) infusions once a week, for the next three weeks, before the training session. LA infusions of muscimol (MUSC), a GABA-A agonist that inhibits neural activity, reduced CS evoked fear-behavior to pre-conditioning levels. LA infusions of pentagastrin (PENT), a cholecystokinin-2 (CCK) agonist that increases neural excitability, resulted in CS-evoked fear-behavior that continued past the offset of the CS. This suggests that neural activity in the LA is required for the retrieval of fear memories that stem from repeated and uncertain reinforcement, and that CCK signaling in the LA plays a role in the recovery from fear after the removal of the fear-evoking stimulus.

Central, but not basolateral, amygdala involvement in the anxiolytic-like effects of midazolam in rats in the elevated plus maze

The role of the amygdala in the mediation of fear and anxiety has been extensively investigated. However, how the amygdala functions during the organization of the anxiety-like behaviors generated in the elevated plus maze (EPM) is still under investigation. The basolateral (BLA) and the central (CeA) nuclei are the main input and output stations of the amygdala. In the present study, we ethopharmacologically analyzed the behavior of rats subjected to the EPM and the tissue content of the monoamines dopamine (DA) and serotonin (5-HT) and their metabolites in the nucleus accumbens (NAc), dorsal hippocampus (DH), and dorsal striatum (DS) of animals injected with saline or midazolam (20 and 30 nmol/0.2 µL) into the BLA or CeA. Injections of midazolam into the CeA, but not BLA, caused clear anxiolytic-like effects in the EPM. These treatments did not cause significant changes in 5-HT or DA contents in the NAc, DH, or DS of animals tested in the EPM. The data suggest that the anxiolytic-like effects of midazolam in the EPM also appear to rely on GABA-benzodiazepine mechanisms in the CeA, but not BLA, and do not appear to depend on 5-HT and DA mechanisms prevalent in limbic structures.

Amygdala microcircuits mediating fear expression and extinction

This review summarizes the latest developments in our understanding of amygdala networks that support classical fear conditioning, the experimental paradigm most commonly used to study learned fear in the laboratory. These recent advances have considerable translational significance as congruent findings from studies of fear learning in animals and humans indicate that anxiety disorders result from abnormalities in the mechanisms that normally regulate conditioned fear. Because of the introduction of new techniques and the continued use of traditional approaches, it is becoming clear that conditioned fear involves much more complex networks than initially believed, including coordinated interactions between multiple excitatory and inhibitory circuits within the amygdala.

The persistence of maladaptive memory: addiction, drug memories and anti-relapse treatments

Addiction is a chronic, relapsing disorder, characterised by the long-term propensity of addicted individuals to relapse. A major factor that obstructs the attainment of abstinence is the persistence of maladaptive drug-associated memories, which can maintain drug-seeking and taking behaviour and promote unconscious relapse of these habits. Thus, addiction can be conceptualised as a disorder of aberrant learning of the formation of strong instrumental memories linking actions to drug-seeking and taking outcomes that ultimately are expressed as persistent stimulus-response habits; of previously neutral environmental stimuli that become associated with drug highs (and/or withdrawal states) through pavlovian conditioning, and of the subsequent interactions between pavlovian and instrumental memories to influence relapse behaviour. Understanding the psychological, neurobiological and molecular basis of these drug memories may produce new methods of pro-abstinence, anti-relapse treatments for addiction.

Orexin, stress, and anxiety/panic states

A panic response is an adaptive response to deal with an imminent threat and consists of an integrated pattern of behavioral (aggression, fleeing, or freezing) and increased cardiorespiratory and endocrine responses that are highly conserved across vertebrate species. In the 1920s and 1940s, Philip Bard and Walter Hess, respectively, determined that the posterior regions of the hypothalamus are critical for a "fight-or-flight" reaction to deal with an imminent threat. Since the 1940s it was determined that the posterior hypothalamic panic area was located dorsal (perifornical hypothalamus: PeF) and dorsomedial (dorsomedial hypothalamus: DMH) to the fornix. This area is also critical for regulating circadian rhythms and in 1998, a novel wake-promoting neuropeptide called orexin (ORX)/hypocretin was discovered and determined to be almost exclusively synthesized in the DMH/PeF perifornical hypothalamus and adjacent lateral hypothalamus. The most proximally emergent role of ORX is in regulation of wakefulness through interactions with efferent systems that mediate arousal and energy homeostasis. A hypoactive ORX system is also linked to narcolepsy. However, ORX role in more complex emotional responses is emerging in more recent studies where ORX is linked to depression and anxiety states. Here, we review data that demonstrates ORX ability to mobilize a coordinated adaptive panic/defense response (anxiety, cardiorespiratory, and endocrine components), and summarize the evidence that supports a hyperactive ORX system being linked to pathological panic and anxiety states.

Evidence for a role of inhibition of orexinergic neurons in the anxiolytic and sedative effects of diazepam: A c-Fos study

The classical benzodiazepine diazepam (DZ) induces anxiolysis at low doses and sedation and hypnosis at higher doses. Different brain areas and neuronal populations most likely mediate these different behavioral effects. We used c-Fos immunohistochemistry as an indirect way to study neuronal activation or inhibition induced by DZ at anxiolytic and sedative doses (0.5 and 5mg/kg, respectively) in various brain areas involved in anxiety, arousal, sedation and addiction in C57BL/6J mice. We also focused on the two neuronal populations, orexinergic and dopaminergic neuronal populations, with the help of double-immunohistochemistry using c-Fos and orexin-A antibodies and c-Fos and tyrosine hydroxylase antibodies. We found that different brain areas of unhabituated mice reacted differently to the mild stress induced by vehicle injection. Also the response to anxiolytic or sedative doses of DZ differed between the areas, suggesting that distinct brain areas mediate the behavioral effects of low and high DZ doses. Our findings propose a role for inhibition of orexin neurons in the anxiolytic and sleep-promoting effects of DZ. In addition, the activation of central amygdala neurons by DZ treatment was associated with anxiolytic and sedative effects. On the other hand, the ventral hippocampus, basolateral amygdala, ventral tegmental area and prefrontal cortex were sensitive even to the mild injection stress, but not to the anxiolytic dose of DZ.

Repeated amphetamine exposure disrupts dopaminergic modulation of amygdala-prefrontal circuitry and cognitive/emotional functioning

Repeated exposure to psychostimulants such as amphetamine (AMPH) disrupts cognitive and behavioral processes mediated by the medial prefrontal cortical (mPFC) and basolateral amygdala (BLA). The present study investigated the effects of repeated AMPH exposure on the neuromodulatory actions of dopamine (DA) on BLA-mPFC circuitry and cognitive/emotional processing mediated by these circuits. Rats received five AMPH (2 mg/kg) or saline injections (controls) over 10 d, followed by 2-4 week drug washout. In vivo neurophysiological extracellular recordings in urethane-anesthetized rats were used to obtain data from mPFC neurons that were either inhibited or excited by BLA stimulation. In controls, acute AMPH attenuated BLA-evoked inhibitory or excitatory responses; these effects were mimicked by selective D(2) or D(1) agonists, respectively. However, in AMPH-treated rats, the ability of these dopaminergic manipulations to modulate BLA-driven decreases/increases in mPFC activity was abolished. Repeated AMPH also blunted the excitatory effects of ventral tegmental area stimulation on mPFC neural firing. Behavioral studies assessed the effect of repeated AMPH on decision making with conditioned punishment, a process mediated by BLA-mPFC circuitry and mesocortical DA. These treatments impaired the ability of rats to use conditioned aversive stimuli (footshock-associated cue) to guide the direction of instrumental responding. Collectively, these data suggest that repeated AMPH exposure can lead to persistent disruption of dopaminergic modulation of BLA-mPFC circuitry, which may underlie impairments in cognitive/emotional processing observed in stimulant abusers. Furthermore, they suggest that impairments in decision making guided by aversive stimuli observed in stimulant abusers may be the result of repeated drug exposure.

Personality influences the neural responses to viewing facial expressions of emotion

Cognitive research has long been aware of the relationship between individual differences in personality and performance on behavioural tasks. However, within the field of cognitive neuroscience, the way in which such differences manifest at a neural level has received relatively little attention. We review recent research addressing the relationship between personality traits and the neural response to viewing facial signals of emotion. In one section, we discuss work demonstrating the relationship between anxiety and the amygdala response to facial signals of threat. A second section considers research showing that individual differences in reward drive (behavioural activation system), a trait linked to aggression, influence the neural responsivity and connectivity between brain regions implicated in aggression when viewing facial signals of anger. Finally, we address recent criticisms of the correlational approach to fMRI analyses and conclude that when used appropriately, analyses examining the relationship between personality and brain activity provide a useful tool for understanding the neural basis of facial expression processing and emotion processing in general.

Animal models of neuropsychiatric disorders

We survey the utility of animal models of mental illness, based on the identification of possible neurocognitive or neurobehavioral endophenotypes. Three broad clusters of neuropsychiatric disorder are discussed: (a) impulsive-compulsive syndromes, comprising drug addiction, attention deficit/hyperactivity disorder, gambling, obsessive-compulsive disorder, and compulsive eating; (b) disorders at the cognitive-emotional interface, comprising anxiety, depression, and schizophrenia; and (c) disorders purely of cognition, which contribute to the third cluster, cognitive disorders. The emphasis is thus on modeling symptoms rather than disorders per se. We also distinguish between two main aspects of any validated model: the precise neurobehavioral or neurocognitive processes implicated from detailed study of the clinical phenotype, and the perturbations, whether typically genetic, environmental, pharmacological, or neurodevelopmental, that are designed to simulate relevant neural, neurochemical, or molecular aspects of particular neuropsychiatric disorders.

Role of amygdala-prefrontal cortex circuitry in regulating the expression of contextual fear memory

The basolateral amygdala (BLA) and medial prefrontal cortex (mPFC) are inter-connected regions involved in fear memory expression. The reciprocal nature of projections between these areas differs along the rostrocaudal extent of BLA. This study investigated the role of functional interactions between BLA and the prelimbic (PL) subregion of mPFC in mediating contextual fear memory. Freezing served as the measure of conditioned fear. Experiments 1-3 examined the effects of left, right or bilateral infusion of bupivacaine into anterior BLA (aBLA), posterior BLA (pBLA) or PL on fear memory expression. Reversible inactivation of left, right or bilateral aBLA impaired fear memory expression. Bilateral inactivation of pBLA or PL also disrupted the expression of fear memory, although left or right inactivation alone had no significant effects in either region. Experiment 4 examined the effects of functionally disconnecting pBLA and PL on contextual fear memory by infusing bupivacaine unilaterally into pBLA and PL in the ipsilateral or contralateral hemisphere. Fear memory expression was impaired by asymmetric inactivation of pBLA and PL; however, a similar effect was also observed with symmetric inactivation of these regions. Bupivacaine infusion did not affect behavior in the open field, likely ruling out non-specific effects of inactivation on innate fear and locomotor activity. These results demonstrate different roles for rostral and caudal BLA in mediating the expression of contextual fear memory. They also raise the possibility that pBLA-PL circuitry is involved in subserving fear memory expression via complex processing mechanisms, although further research is needed to confirm this preliminary finding.

Differentiable contributions of human amygdalar subregions in the computations underlying reward and avoidance learning

To understand how the human amygdala contributes to associative learning, it is necessary to differentiate the contributions of its subregions. However, major limitations in the techniques used for the acquisition and analysis of functional magnetic resonance imaging (fMRI) data have hitherto precluded segregation of function with the amygdala in humans. Here, we used high-resolution fMRI in combination with a region-of-interest-based normalization method to differentiate functionally the contributions of distinct subregions within the human amygdala during two different types of instrumental conditioning: reward and avoidance learning. Through the application of a computational-model-based analysis, we found evidence for a dissociation between the contributions of the basolateral and centromedial complexes in the representation of specific computational signals during learning, with the basolateral complex contributing more to reward learning, and the centromedial complex more to avoidance learning. These results provide unique insights into the computations being implemented within fine-grained amygdala circuits in the human brain.

Lesions of the basolateral amygdala and orbitofrontal cortex differentially affect acquisition and performance of a rodent gambling task

Risky decision making on the Iowa Gambling Task (IGT) has been observed in several psychiatric disorders, including substance abuse, schizophrenia, and pathological gambling. Such deficits are often attributed to impaired processing within the orbitofrontal cortex (OFC) because patients with damage to this area or to the amygdala, which is strongly interconnected with the OFC, can likewise show enhanced choice of high-risk options. However, whether damage to the OFC or amygdala impairs subjects' ability to learn the task, or actually affects the decision-making process itself, is currently unclear. To address these issues, rats were trained to perform a rodent gambling task (rGT) either before or after bilateral excitotoxic lesions to the basolateral amygdala (BLA) or OFC. Maximum profits in both the rGT and IGT are obtained by favoring smaller rewards associated with lower penalties, and avoiding the tempting, yet ultimately disadvantageous, large reward options. Lesions of the OFC or BLA made before task acquisition initially impaired animals' ability to determine the optimal strategy, but did not disrupt decision making in the long term. In contrast, lesions of the BLA, but not the OFC, made after the task had been acquired increased risky choice. These results suggest that, although both regions contribute to the development of appropriate choice behavior under risk, the BLA maintains a more fundamental role in guiding these decisions. The maladaptive choice pattern observed on the IGT in patients with OFC lesions could therefore partially reflect a learning deficit, whereas amygdala damage may give rise to a more robust decision-making impairment.

Basolateral amygdala responds robustly to social calls: spiking characteristics of single unit activity

Vocalizations emitted within a social context can trigger call-specific changes in the emotional and physiological/autonomic state of the receiver. The amygdala is implicated in mediating these changes, but its role in call perception remains relatively unexplored. We examined call and pitch selectivity of single neurons within the basolateral amygdala (BLA) by recording spiking activity in response to 5 pitch variants of each of 14 species-specific calls presented to awake, head-restrained mustached bats, Pteronotus parnellii. A response-wise analysis across neurons revealed seven types of temporal response patterns based on the timing and duration of spiking. Roughly half of the responses to different call types were significantly affected by changes in call pitch. A neuron-wise analysis revealed that ∼ 12% (8/69) of the neurons preferred the same pitch across all call types. Ninety-three percent (93/100) of neurons were excited by at least one call type and 76% exhibited either complete or transient suppression to one or more call types. The majority of neurons preferred fewer than half of the 14 different simple-syllabic calls. A call-wise analysis of spiking activity revealed that call types signaling either threat or fear most consistently evoked increases in the spike rate. In contrast, calls emitted during appeasement tended to evoke spike suppression. Our data suggest that BLA neurons participate in the processing of multiple call types and exhibit a rich variety of temporal response patterns that are neither neuron nor call specific.

Conceptual similarity promotes generalization of higher order fear learning

We tested the hypothesis that conceptual similarity promotes generalization of conditioned fear. Using a sensory preconditioning procedure, three groups of subjects learned an association between two cues that were conceptually similar, unrelated, or mismatched. Next, one of the cues was paired with a shock. The other cue was then reintroduced to test for fear generalization, as measured by the skin conductance response. Results showed enhanced fear generalization that correlated with trait anxiety levels in the group that learned an association between conceptually similar stimuli. These findings suggest that conceptual representations of conditional stimuli influence human fear learning processes.

A cation-π interaction at a phenylalanine residue in the glycine receptor binding site is conserved for different agonists

Cation-π interactions have been demonstrated to play a major role in agonist-binding in Cys-loop receptors. However, neither the aromatic amino acid contributing to this interaction nor its location is conserved among Cys-loop receptors. Likewise, it is not clear how many different agonists of a given receptor form a cation-π interaction or, if they do, whether it is with the same aromatic amino acid as the major physiological agonist. We demonstrated previously that Phe159 in the glycine receptor (GlyR) α1 subunit forms a strong cation-π interaction with the principal agonist, glycine. In the current study, we investigated whether the lower efficacy agonists of the human GlyR β-alanine and taurine also form cation-π interactions with Phe159. By incorporating a series of unnatural amino acids, we found cation-π interactions between Phe159 and the amino groups of β-alanine and taurine. The strengths of these interactions were significantly weaker than for glycine. Modeling studies suggest that β-alanine and taurine are orientated subtly differently in the binding pocket, with their amino groups further from Phe159 than that of glycine. These data therefore show that similar agonists can have similar but not identical orientations and interactions in the binding pocket and provide a possible explanation for the lower potencies of β-alanine and taurine.