Contributions of the Central Extended Amygdala to Fear and Anxiety

It is widely thought that phasic and sustained responses to threat reflect dissociable circuits centered on the central nucleus of the amygdala (Ce) and the bed nucleus of the stria terminalis (BST), the two major subdivisions of the central extended amygdala. Early versions of this hypothesis remain highly influential and have been incorporated into the National Institute of Mental Health Research Research Domain Criteria framework. However, new observations encourage a different perspective. Anatomical studies show that the Ce and BST form a tightly interconnected unit, where different kinds of threat-relevant information can be integrated and used to assemble states of fear and anxiety. Imaging studies in humans and monkeys show that the Ce and BST exhibit similar functional profiles. Both regions are sensitive to a range of aversive challenges, including uncertain or temporally remote threat; both covary with concurrent signs and symptoms of fear and anxiety; both show phasic responses to short-lived threat; and both show heightened activity during sustained exposure to diffusely threatening contexts. Mechanistic studies demonstrate that both regions can control the expression of fear and anxiety during sustained exposure to diffuse threat. These observations compel a reconsideration of the central extended amygdala's contributions to fear and anxiety and its role in neuropsychiatric disease.

Related papers:

title: Elevated responding to safe conditions as a specific risk factor for anxiety versus depressive disorders: evidence from a longitudinal investigation.
abstract: The current study evaluated the degree to which startle reflexes (SRs) in safe conditions versus danger conditions were predictive of the onset of anxiety disorders. Specificity of these effects to anxiety disorders was evaluated in comparison to unipolar depressive disorders and with consideration of level of neuroticism. A startle paradigm was administered at baseline to 132 nondisordered adolescents as part of a longitudinal study examining risk factors for emotional disorders. Participants underwent a repetition of eight safe-danger sequences and were told that delivery of an aversive stimulus leading to a muscle contraction of the arm would occur only in the late part of danger conditions. One aversive stimulus occurred midway in the safe-danger sequences. Participants were assessed for the onset of anxiety and unipolar depressive disorders annually over the next 3 to 4 years. Larger SR magnitude during safe conditions following delivery of the aversive stimulus predicted the subsequent first onset of anxiety disorders. Moreover, prediction of the onset of anxiety disorders remained significant above and beyond the effects of comorbid unipolar depression, neuroticism, and subjective ratings of intensity of the aversive stimulus. In sum, elevated responding to safe conditions following an aversive stimulus appears to be a specific, prospective risk factor for the first onset of anxiety disorders.

title: Rethinking the Fear Circuit: The Central Nucleus of the Amygdala Is Required for the Acquisition, Consolidation, and Expression of Pavlovian Fear Conditioning
abstract: In the standard model of pavlovian fear learning, sensory input from neutral and aversive stimuli converge in the lateral nucleus of the amygdala (LA), in which alterations in synaptic transmission encode the association. During fear expression, the LA is thought to engage the central nucleus of the amygdala (CE), which serves as the principal output nucleus for the expression of conditioned fear responses. In the present study, we reexamined the roles of LA and CE. Specifically, we asked whether CE, like LA, might also be involved in fear learning and memory consolidation. Using functional inactivation methods, we first show that CE is involved not only in the expression but also the acquisition of fear conditioning. Next, we show that inhibition of protein synthesis in CE after training impairs fear memory consolidation. These findings indicate that CE is not only involved in fear expression but, like LA, is also involved in the learning and consolidation of pavlovian fear conditioning.

title: Uncertainty and anticipation in anxiety: an integrated neurobiological and psychological perspective
abstract: Uncertainty about a possible future threat disrupts our ability to avoid it or to mitigate its negative impact and thus results in anxiety. Here, we focus the broad literature on the neurobiology of anxiety through the lens of uncertainty. We identify five processes that are essential for adaptive anticipatory responses to future threat uncertainty and propose that alterations in the neural instantiation of these processes result in maladaptive responses to uncertainty in pathological anxiety. This framework has the potential to advance the classification, diagnosis and treatment of clinical anxiety.

title: Neural substrates of individual differences in human fear learning: Evidence from concurrent fMRI, fear-potentiated startle, and US-expectancy data
abstract: To provide insight into individual differences in fear learning, we examined the emotional and cognitive expressions of discriminative fear conditioning in direct relation to its neural substrates. Contrary to previous behavioral–neural (fMRI) research on fear learning—in which the emotional expression of fear was generally indexed by skin conductance—we used fear-potentiated startle, a more reliable and specific index of fear. While we obtained concurrent fear-potentiated startle, neuroimaging (fMRI), and US-expectancy data, healthy participants underwent a fear-conditioning paradigm in which one of two conditioned stimuli (CS+ but not CS–) was paired with a shock (unconditioned stimulus [US]). Fear learning was evident from the differential expressions of fear (CS+ > CS–) at both the behavioral level (startle potentiation and US expectancy) and the neural level (in amygdala, anterior cingulate cortex, hippocampus, and insula). We examined individual differences in discriminative fear conditioning by classifying participants (as conditionable vs. unconditionable) according to whether they showed successful differential startle potentiation. This revealed that the individual differences in the emotional expression of discriminative fear learning (startle potentiation) were reflected in differential amygdala activation, regardless of the cognitive expression of fear learning (CS–US contingency or hippocampal activation). Our study provides the first evidence for the potential of examining startle potentiation in concurrent fMRI research on fear learning.

title: A translational neuroscience approach to understanding the development of social anxiety disorder and its pathophysiology.
abstract: This review brings together recent research from molecular, neural circuit, animal model, and human studies to help understand the neurodevelopmental mechanisms underlying social anxiety disorder. Social anxiety disorder is common and debilitating, and it often leads to further psychopathology. Numerous studies have demonstrated that extremely behaviorally inhibited and temperamentally anxious young children are at marked risk of developing social anxiety disorder. Recent work in human and nonhuman primates has identified a distributed brain network that underlies early-life anxiety including the central nucleus of the amygdala, the anterior hippocampus, and the orbitofrontal cortex. Studies in nonhuman primates have demonstrated that alterations in this circuit are trait-like in that they are stable over time and across contexts. Notably, the components of this circuit are differentially influenced by heritable and environmental factors, and specific lesion studies have demonstrated a causal role for multiple components of the circuit. Molecular studies in rodents and primates point to disrupted neurodevelopmental and neuroplastic processes within critical components of the early-life dispositional anxiety neural circuit. The possibility of identifying an early-life at-risk phenotype, along with an understanding of its neurobiology, provides an unusual opportunity to conceptualize novel preventive intervention strategies aimed at reducing the suffering of anxious children and preventing them from developing further psychopathology.

title: Functional neuroimaging of major depressive disorder: a meta-analysis and new integration of base line activation and neural response data.
abstract: Functional neuroimaging investigations of major depressive disorder can advance both the neural theory and treatment of this debilitating illness. Inconsistency of neuroimaging findings and the use of region-of-interest approaches have hindered the development of a comprehensive, empirically informed neural model of major depression. In this context, the authors sought to identify reliable anomalies in baseline neural activity and neural response to affective stimuli in major depressive disorder.



The authors applied voxel-wise, whole-brain meta-analysis to neuroimaging investigations comparing depressed to healthy comparison groups with respect to baseline neural activity or neural response to positively and/or negatively valenced stimuli.



Relative to healthy subjects, those with major depression had reliably higher baseline activity, bilaterally, in the pulvinar nucleus. The analysis of neural response studies using negative stimuli showed greater response in the amygdala, insula, and dorsal anterior cingulate cortex and lower response in the dorsal striatum and dorsolateral prefrontal cortex in individuals with major depressive disorder than in healthy subjects.



The meta-analytic results support an elegant and neuroanatomically viable model of the salience of negative information in major depressive disorder. In this proposed model, high baseline pulvinar activity in depression first potentiates responding of the brain's salience network to negative information; next, and owing potentially to low striatal dopamine levels in depression, this viscerally charged information fails to propagate up the cortical-striatal-pallidalthalamic circuit to the dorsolateral prefrontal cortex for contextual processing and reappraisal.

title: Fear Conditioning Potentiates Synaptic Transmission onto Long-Range Projection Neurons in the Lateral Subdivision of Central Amygdala
abstract: Recent studies indicate that the lateral subdivision of the central amygdala (CeL) is essential for fear learning. Specifically, fear conditioning induces cell-type-specific synaptic plasticity in CeL neurons that is required for the storage of fear memories. The CeL also controls fear expression by gating the activity of the medial subdivision of the central amygdala (CeM), the canonical amygdala output to areas that mediate defensive responses. In addition to the connection with CeM, the CeL sends long-range projections to innervate extra-amygdala areas. However, the long-range projection CeL neurons have not been well characterized, and their role in fear regulation is unknown. Here we show in mice that a subset of CeL neurons directly project to the midbrain periaqueductal gray (PAG) and the paraventricular nucleus of the thalamus, two brain areas implicated in defensive behavior. These long-range projection CeL neurons are predominantly somatostatin-positive (SOM+) neurons, which can directly inhibit PAG neurons, and some of which innervate both the PAG and paraventricular nucleus of the thalamus. Notably, fear conditioning potentiates excitatory synaptic transmission onto these long-range projection CeL neurons. Thus, our study identifies a subpopulation of SOM+ CeL neurons that may contribute to fear learning and regulate fear expression independent of CeM.

title: Knowing how much you don't know: a neural organization of uncertainty estimates
abstract: How we estimate uncertainty is important in decision neuroscience and has wide-ranging implications in basic and clinical neuroscience, from computational models of optimality to ideas on psychopathological disorders including anxiety, depression and schizophrenia. Empirical research in neuroscience, which has been based on divergent theoretical assumptions, has focused on the fundamental question of how uncertainty is encoded in the brain and how it influences behaviour. Here, we integrate several theoretical concepts about uncertainty into a decision-making framework. We conclude that the currently available evidence indicates that distinct neural encoding (including summary statistic-type representations) of uncertainty occurs in distinct neural systems.

title: Initial and sustained brain responses to contextual conditioned anxiety in humans
abstract: Contextual fear conditioning takes place if the occurrence of threat cannot be predicted by specific cues. As a consequence the context becomes the best predictor of the threat and later induces anxiety (sustained fear response). Previous studies suggest that both the amygdala and the hippocampus are crucial for contextual fear conditioning. First, we wanted to further elucidate the neuronal correlates of long-lasting contextual threat within a highly ecologically setting created in virtual reality (VR). Second, we wanted to distinguish between initial and sustained components of the anxiety response to a threatening situation. Twenty-four participants were guided through two virtual offices for 30s each. They received unpredictable electric stimuli (unconditioned stimulus, US) in one office (anxiety context, CXT+), but never in the second office (safety context, CXT-). Successful contextual fear conditioning was indexed by higher anxiety and enhanced US-expectancy ratings for CXT+ versus CXT-. Initial neural activity was assessed by modeling the onsets of both contexts, and sustained neural activity by considering the entire context duration (contrasts: CXT+ > CXT-). Amygdala and hippocampus revealed sustained activity. Initial and sustained activities were found in the middle temporal gyrus, and primary motor cortex (M1). Additional initial activity was obvious in orbitofrontal (OFC), dorsomedial (dmPFC), and dorsolateral prefrontal cortex (dlPFC). These results suggest that entering a threatening context initially induces conditioned fear reactions (M1), recall of contingency awareness (dlPFC), and explicit threat appraisal (dmPFC, OFC). While remaining in the threatening context might involve anxiety-like conditioned responses (amygdala, M1) and the generation of a spatial map to predict where and when a threatening event may occur (hippocampus). We conclude that in humans initial versus sustained anxiety responses triggered by a threat associated context are associated with distinguishable brain activation patterns involving a fear network and a "contingency-cognitive" network, respectively.

title: Activity in the human amygdala corresponds to early, rather than late period autonomic responses to a signal for shock.
abstract: Laboratory animal and human subject studies report that the amygdala is a critical brain structure that supports the acquisition and expression of conditional fear. Recent functional neuroimaging studies in humans have reported that activity in this region is closely related to the behavioral expression of conditional skin conductance responses (SCR). However, SCR waveforms following conditional stimulus (CS) presentation contain both early period and late period responses that may differ with respect to underlying central processes. It is not known whether amygdala activity corresponds to the expression of early conditional responses (CRs) that occur shortly following CS onset or late CRs that closely precede UCS onset. The present study used event-related functional magnetic resonance imaging and concurrent skin conductance measurements to determine whether amygdala activity is more closely related to the expression of early or late period CRs. Increased amygdala activity was detected during the formation of early, but not late period CRs. Additionally, this pattern of amygdala activity did not dissipate, but persisted into late stages of the experiment. These findings are consistent with the idea that amygdala responding is critically involved in the generation of CRs formed shortly following CS onset.

title: The Rhesus Monkey Brain in Stereotaxic Coordinates
abstract: The Rhesus Monkey Brain in Stereotaxic Coordinates is the most comprehensive and accurate atlas of the monkey brain currently available. The second edition of this classic book is a complete revision, featuring many improvements and upgrades. Constructed by the established leaders in neuroanatomical atlas development, the new edition will again be the indispensable resource for all scientists working on the primate nervous system. * 151 coronal diagrams and 151 accompanying photographic plates spaced at 120 m intervals; diagrams completely revised * 60 photographic coronal plates of SMI immunoreactivity; delineations completely revised. New in this edition * DVD with all drawings in Adobe Acrobat (r) pdf format as well as eps files of photographic plates * Inclusion in the DVD of 3D reconstructions of the diagrammatic atlas done by two major teams headed by Rolf Kotter and Louis Collins * Linking of structure names from the atlas to the CoCoMac neuroinformatics database for online retrieval of additional information on partitioning schemes and connectivity * Inclusion of MR images at approximately the same levels as the coronal diagrams * This monkey brain atlas follows the same nomenclature and abbreviations conventions as the mouse, rat, chicken, and human brain atlases published under George Paxinos' leadership

title: The Rat Brain in Stereotaxic Coordinates

title: Overshadowed by the amygdala: the bed nucleus of the stria terminalis emerges as key to psychiatric disorders
abstract: The bed nucleus of the stria terminalis (BNST) is a center of integration for limbic information and valence monitoring. The BNST, sometimes referred to as the extended amygdala, is located in the basal forebrain and is a sexually dimorphic structure made up of between 12 and 18 sub-nuclei. These sub-nuclei are rich with distinct neuronal subpopulations of receptors, neurotransmitters, transporters and proteins. The BNST is important in a range of behaviors such as: the stress response, extended duration fear states and social behavior, all crucial determinants of dysfunction in human psychiatric diseases. Most research on stress and psychiatric diseases has focused on the amygdala, which regulates immediate responses to fear. However, the BNST, and not the amygdala, is the center of the psychogenic circuit from the hippocampus to the paraventricular nucleus. This circuit is important in the stimulation of the hypothalamic–pituitary–adrenal axis. Thus, the BNST has been largely overlooked with respect to its possible dysregulation in mood and anxiety disorders, social dysfunction and psychological trauma, all of which have clear gender disparities. In this review, we will look in-depth at the anatomy and projections of the BNST, and provide an overview of the current literature on the relevance of BNST dysregulation in psychiatric diseases.

title: Connectivity between the central nucleus of the amygdala and the bed nucleus of the stria terminalis in the non-human primate: neuronal tract tracing and developmental neuroimaging studies
abstract: The lateral division of the bed nucleus of the stria terminalis (BSTL) and central nucleus of the amygdala (Ce) form the two poles of the ‘central extended amygdala’, a theorized subcortical macrostructure important in threat-related processing. Our previous work in nonhuman primates, and humans, demonstrating strong resting fMRI connectivity between the Ce and BSTL regions, provides evidence for the integrated activity of these structures. To further understand the anatomical substrates that underlie this coordinated function, and to investigate the integrity of the central extended amygdala early in life, we examined the intrinsic connectivity between the Ce and BSTL in non-human primates using ex vivo neuronal tract tracing, and in vivo diffusion-weighted imaging and resting fMRI techniques. The tracing studies revealed that BSTL receives strong input from Ce; however, the reciprocal pathway is less robust, implying that the primate Ce is a major modulator of BSTL function. The sublenticular extended amygdala (SLEAc) is strongly and reciprocally connected to both Ce and BSTL, potentially allowing the SLEAc to modulate information flow between the two structures. Longitudinal early-life structural imaging in a separate cohort of monkeys revealed that extended amygdala white matter pathways are in place as early as 3 weeks of age. Interestingly, resting functional connectivity between Ce and BSTL regions increases in coherence from 3 to 7 weeks of age. Taken together, these findings demonstrate a time period during which information flow between Ce and BSTL undergoes postnatal developmental changes likely via direct Ce → BSTL and/or Ce ↔ SLEAc ↔ BSTL projections.

title: BNST neurocircuitry in humans
abstract: Anxiety and addiction disorders are two of the most common mental disorders in the United States, and are typically chronic, disabling, and comorbid. Emerging evidence suggests the bed nucleus of the stria terminalis (BNST) mediates both anxiety and addiction through connections with other brain regions, including the amygdala and nucleus accumbens. Although BNST structural connections have been identified in rodents and a limited number of structural connections have been verified in non-human primates, BNST connections have yet to be described in humans. Neuroimaging is a powerful tool for identifying structural and functional circuits in vivo. In this study, we examined BNST structural and functional connectivity in a large sample of humans. The BNST showed structural and functional connections with multiple subcortical regions, including limbic, thalamic, and basal ganglia structures, confirming structural findings in rodents. We describe two novel connections in the human brain that have not been previously reported in rodents or non-human primates, including a structural connection with the temporal pole, and a functional connection with the paracingulate gyrus. The findings of this study provide a map of the BNST's structural and functional connectivity across the brain in healthy humans. In large part, the BNST neurocircuitry in humans is similar to the findings from rodents and non-human primates; however, several connections are unique to humans. Future explorations of BNST neurocircuitry in anxiety and addiction disorders have the potential to reveal novel mechanisms underlying these disabling psychiatric illnesses.

title: Resting state connectivity of the bed nucleus of the stria terminalis at ultra‐high field
abstract: The bed nucleus of the stria terminalis (BNST), a portion of the “extended amygdala,” is implicated in the pathophysiology of anxiety and addiction disorders. Its small size and connection to other small regions prevents standard imaging techniques from easily capturing it and its connectivity with confidence. Seed‐based resting state functional connectivity is an established method for mapping functional connections across the brain from a region of interest. We, therefore, mapped the BNST resting state network with high spatial resolution using 7 Tesla fMRI, demonstrating the in vivo reproduction of many human BNST connections previously described only in animal research. We identify strong BNST functional connectivity in amygdala, hippocampus and thalamic subregions, caudate, periaqueductal gray, hypothalamus, and cortical areas such as the medial PFC and precuneus. This work, which demonstrates the power of ultra‐high field for mapping functional connections in the human, is an important step toward elucidating cortical and subcortical regions and subregions of the BNST network.  Brain Mapp 36:4076–4088, 2015.

title: Interactions between transient and sustained neural signals support the generation and regulation of anxious emotion.
abstract: Anxious emotion can manifest on brief (threat response) and/or persistent (chronic apprehension and arousal) timescales, and prior work has suggested that these signals are supported by separable neural circuitries. This fMRI study utilized a mixed block-event-related emotional provocation paradigm in 55 healthy participants to simultaneously measure brief and persistent anxious emotional responses, testing the specificity of, and interactions between, these potentially distinct systems. Results indicated that components of emotional processing networks were uniquely sensitive to transient and sustained anxious emotion. Whereas the amygdala and midbrain showed only transient responses, the ventral basal forebrain and anterior insula showed sustained activity during extended emotional contexts that tracked positively with task-evoked anxiety. States of lesser anxiety were associated with greater sustained activity in the ventromedial prefrontal cortex. Furthermore, ventromedial prefrontal recruitment was lower in individuals with higher scores on intolerance of uncertainty measures, and this hyporecruitment predicted greater transient amygdala responding to potential threat cues. This work demonstrates how brain circuitries interact across temporal scales to support brief and persistent anxious emotion and suggests potentially divergent mechanisms of dysregulation in clinical syndromes marked by brief versus persistent symptoms of anxiety.

title: Contextual startle responses moderate the relation between behavioral inhibition and anxiety in middle childhood.
abstract: Behavioral inhibition (BI), a temperament characterized in early childhood by wariness and avoidance of novelty, is a risk factor for anxiety disorders. An enhanced startle response has been observed in adolescents characterized with BI in childhood, particularly when they also manifest concurrent symptoms of anxiety. However, no prior study has examined relations among BI, startle responsivity, and anxiety in a prospective manner. Data for the present study were from a longitudinal study of infant temperament. Maternal reports and observations of BI were assessed at ages 2 and 3. At age 7, participants completed a startle procedure, while electromyography was collected, where participants viewed different colors on a screen that were associated with either the delivery of an aversive stimulus (i.e., puff of air to the larynx; threat cue) or the absence of the aversive stimulus (i.e., safety cue). Parental reports of child anxiety were collected when children were 7 and 9 years of age. Results revealed that startle responses at age 7 moderated the relation between early BI and 9-year anxiety. These findings provide insight into one potential mechanism that may place behaviorally inhibited children at risk for anxiety.

title: Functional atlas of emotional faces processing: a voxel-based meta-analysis of 105 functional magnetic resonance imaging studies.
abstract: Most of our social interactions involve perception of emotional information from the faces of other people. Furthermore, such emotional processes are thought to be aberrant in a range of clinical disorders, including psychosis and depression. However, the exact neurofunctional maps underlying emotional facial processing are not well defined.



Two independent researchers conducted separate comprehensive PubMed (1990 to May 2008) searches to find all functional magnetic resonance imaging (fMRI) studies using a variant of the emotional faces paradigm in healthy participants. The search terms were: "fMRI AND happy faces," "fMRI AND sad faces," "fMRI AND fearful faces," "fMRI AND angry faces," "fMRI AND disgusted faces" and "fMRI AND neutral faces." We extracted spatial coordinates and inserted them in an electronic database. We performed activation likelihood estimation analysis for voxel-based meta-analyses.



Of the originally identified studies, 105 met our inclusion criteria. The overall database consisted of 1785 brain coordinates that yielded an overall sample of 1600 healthy participants. Quantitative voxel-based meta-analysis of brain activation provided neurofunctional maps for 1) main effect of human faces; 2) main effect of emotional valence; and 3) modulatory effect of age, sex, explicit versus implicit processing and magnetic field strength. Processing of emotional faces was associated with increased activation in a number of visual, limbic, temporoparietal and prefrontal areas; the putamen; and the cerebellum. Happy, fearful and sad faces specifically activated the amygdala, whereas angry or disgusted faces had no effect on this brain region. Furthermore, amygdala sensitivity was greater for fearful than for happy or sad faces. Insular activation was selectively reported during processing of disgusted and angry faces. However, insular sensitivity was greater for disgusted than for angry faces. Conversely, neural response in the visual cortex and cerebellum was observable across all emotional conditions.



Although the activation likelihood estimation approach is currently one of the most powerful and reliable meta-analytical methods in neuroimaging research, it is insensitive to effect sizes.



Our study has detailed neurofunctional maps to use as normative references in future fMRI studies of emotional facial processing in psychiatric populations. We found selective differences between neural networks underlying the basic emotions in limbic and insular brain regions.

title: TOWARD AN ACCOUNT OF CLINICAL ANXIETY PREDICATED ON BASIC, NEURALLY MAPPED MECHANISMS OF PAVLOVIAN FEAR‐LEARNING: THE CASE FOR CONDITIONED OVERGENERALIZATION
abstract: The past two decades have brought dramatic progress in the neuroscience of anxiety due, in no small part, to animal findings specifying the neurobiology of Pavlovian fear‐conditioning. Fortuitously, this neurally mapped process of fear learning is widely expressed in humans, and has been centrally implicated in the etiology of clinical anxiety. Fear‐conditioning experiments in anxiety patients thus represent a unique opportunity to bring recent advances in animal neuroscience to bear on working, brain‐based models of clinical anxiety. The current presentation details the neural basis and clinical relevance of fear conditioning, and highlights generalization of conditioned fear to stimuli resembling the conditioned danger cue as one of the more robust conditioning markers of clinical anxiety. Studies testing such generalization across a variety of anxiety disorders (panic, generalized anxiety disorder, and social anxiety disorder) with systematic methods developed in animals will next be presented. Finally, neural accounts of overgeneralization deriving from animal and human data will be described with emphasis given to implications for the neurobiology and treatment of clinical anxiety.

title: Subgenual Prefrontal Cortex Activity Predicts Individual Differences in Hypothalamic-Pituitary-Adrenal Activity Across Different Contexts
abstract: Hypothalamic-pituitary-adrenal (HPA) system activation is adaptive in response to stress, and HPA dysregulation occurs in stress-related psychopathology. It is important to understand the mechanisms that modulate HPA output, yet few studies have addressed the neural circuitry associated with HPA regulation in primates and humans. Using high-resolution F-18-fluorodeoxyglucose positron emission tomography (FDG-PET) in rhesus monkeys, we assessed the relation between individual differences in brain activity and HPA function across multiple contexts that varied in stressfulness.



Using a logical AND conjunctions analysis, we assessed cortisol and brain metabolic activity with FDG-PET in 35 adolescent rhesus monkeys exposed to two threat and two home-cage conditions. To test the robustness of our findings, we used similar methods in an archival data set. In this data set, brain metabolic activity and cortisol were assessed in 17 adolescent male rhesus monkeys that were exposed to three stress-related contexts.



Results from the two studies revealed that subgenual prefrontal cortex (PFC) metabolism (Brodmann's area 25/24) consistently predicted individual differences in plasma cortisol concentrations regardless of the context in which brain activity and cortisol were assessed.



These findings suggest that activation in subgenual PFC may be related to HPA output across a variety of contexts (including familiar settings and novel or threatening situations). Individuals prone to elevated subgenual PFC activity across multiple contexts may be individuals who consistently show heightened cortisol and may be at risk for stress-related HPA dysregulation.

title: Human Amygdala Activation during Conditioned Fear Acquisition and Extinction: a Mixed-Trial fMRI Study
abstract: Echoplanar functional magnetic resonance imaging (fMRI) was used in normal human subjects to investigate the role of the amygdala in conditioned fear acquisition and extinction. A simple discrimination procedure was employed in which activation to a visual cue predicting shock (CS+) was compared with activation to another cue presented alone (CS-). CS+ and CS- trial types were intermixed in a pseudorandom order. Functional images were acquired with an asymmetric spin echo pulse sequence from three coronal slices centered on the amygdala. Activation of the amygdala/periamygdaloid cortex was observed during conditioned fear acquisition and extinction. The extent of activation during acquisition was significantly correlated with autonomic indices of conditioning in individual subjects. Consistent with a recent electrophysiological recording study in the rat (Quirk et al., 1997), the profile of the amygdala response was temporally graded, although this dynamic was only statistically reliable during extinction. These results provide further evidence for the conservation of amygdala function across species and implicate an amygdalar contribution to both acquisition and extinction processes during associative emotional learning tasks.

title: Dorsomedial Prefrontal Cortex Mediates the Impact of Serotonin Transporter Linked Polymorphic Region Genotype on Anticipatory Threat Reactions
abstract: Excessive anticipatory reactions to potential future adversity are observed across a range of anxiety disorders, but the neurogenetic mechanisms driving interindividual differences are largely unknown. We aimed to discover and validate a gene-brain-behavior pathway by linking presumed genetic risk for anxiety-related psychopathology, key neural activity involved in anxious anticipation, and resulting aversive emotional states.



The functional neuroanatomy of aversive anticipation was probed through functional magnetic resonance imaging in two independent samples of healthy subjects (n = 99 and n = 69), and we studied the influence of genetic variance in the serotonin transporter linked polymorphic region (5-HTTLPR). Skin conductance and startle data served as objective psychophysiological indices of the intensity of individuals' anticipatory responses to potential threat.



Threat cues signaling risk of future electrical shock activated the dorsomedial prefrontal cortex (dmPFC), anterior insula, bed nucleus of the stria terminalis, thalamus, and midbrain consistently across both samples. Threat-related dmPFC activation was enhanced in 5-HTTLPR short allele carriers in sample 1 and this effect was validated in sample 2. Critically, we show that this region mediates the increase in anticipatory psychophysiological reactions in short allele carriers indexed by skin conductance (experiment 1) and startle reactions (experiment 2).



The converging results from these experiments demonstrate that innate 5-HTTLPR linked variation in dmPFC activity predicts psychophysiological responsivity to pending threats. Our results reveal a neurogenetic pathway mediating interindividual variability in anticipatory responses to threat and yield a novel mechanistic account for previously reported associations between genetic variability in serotonin transporter function and stress-related psychopathology.

title: The 3-second auditory conditioned stimulus is a more effective stressor than the 20-second auditory conditioned stimulus in male rats
abstract: Using fear-conditioning model, we have used a 3-s auditory conditioned stimulus (CS) as a stressor and observed fear and stress responses during a specific experimental period regardless of the presence or absence of the CS. Because the CS was extremely short compared with the experimental period, we observed responses primarily in the absence of the CS. In contrast, most studies in the literature have analyzed responses in the presence of the CS. Therefore, the characteristics of fear and stress responses in the absence of the CS remain to be clarified. To clarify this, we compared the characteristics of fear and stress responses elicited by a 3-s auditory CS with those observed during a 20-s auditory CS. The basolateral complex of the amygdala (BLA), but not the bed nucleus of the stria terminalis (BNST), participated in the fear response elicited by the 3-s CS, whereas both the BLA and BNST were involved in the response observed during the 20-s CS. Additional analyses revealed that the BNST participated in the fear response during the 20-s CS when the CS was paired with a 0.75-mA, but not with a 0.9-mA, foot shock, and to the contextual CS. In addition, the fear response elicited by the 3-s CS was more resistant to extinction than that during the 20-s CS. Finally, the 3-s CS produced more intense freezing and corticosterone secretion than the 20-s CS. On the basis of these characteristics, we conclude that the 3-s auditory CS is a more effective stressor than the 20-s auditory CS. Our findings also suggest that foot shock intensity is an additional determinant in the type of fear response induced by the CS.

title: Segregating the significant from the mundane on a moment-to-moment basis via direct and indirect amygdala contributions
abstract: If the amygdala is involved in shaping perceptual experience when affectively significant visual items are encountered, responses in this structure should be correlated with both visual cortex responses and behavioral reports. Here, we investigated how affective significance shapes visual perception during an attentional blink paradigm combined with aversive conditioning. Behaviorally, following aversive learning, affectively significant scenes (CS+) were better detected than neutral (CS−) ones. In terms of mean brain responses, both amygdala and visual cortical responses were stronger during CS+ relative to CS− trials. Increased brain responses in these regions were associated with improved behavioral performance across participants and followed a mediation-like pattern. Importantly, the mediation pattern was observed in a trial-by-trial analysis, revealing that the specific pattern of trial-by-trial variability in brain responses was closely related to single-trial behavioral performance. Furthermore, the influence of the amygdala on visual cortical responses was consistent with a mediation, although partial, via frontal brain regions. Our results thus suggest that affective significance potentially determines the fate of a visual item during competitive interactions by enhancing sensory processing through both direct and indirect paths. In so doing, the amygdala helps separate the significant from the mundane.

title: Mouse defensive behaviors: pharmacological and behavioral assays for anxiety and panic
abstract: The natural defensive behaviors of laboratory mice have been evaluated in both seminatural and highly structured situations; and characterized in terms of eliciting stimuli, response to pharmacological agents, behavior patterns, and outcome or effect on the social and physical environment. The defense patterns of laboratory mice and rats are generally similar, but mice show risk assessment on initial exposure to highly threatening stimuli while rats do not, while rats display alarm vocalizations, missing in mice. Quantitative differences in freezing and flight for laboratory mice and rats appear to largely reflect domestication effects, with wild mice and rats more similar to each other. This nexus of detailed within-species and comparative data on defense patterns makes it possible to reliably elicit specific defenses in mice or rats in an experimental context, providing well-validated assays of the natural defensive behaviors themselves, as opposed to 'models' of defense. The mouse--rat comparisons indicate considerable cross-species generality for these defense patterns, as does a scattered but considerable literature on other mammalian species, generally involving field studies and typically focusing on those aspects of defensive behavior that are visible at a distance, such as vigilance, or flight. Although potential homologies between normal mouse and human defense systems should ideally involve all four pattern components (stimulus, organismic factors, response characteristics, outcome), predictive validity in terms of response to drugs active against specific defensive psychopathology is the most extensively investigated of these. Flight, as measured in the Mouse Defense Test Battery shows a consistently appropriate response to panicolytic, panicogenic, and panic-neutral drugs, while some other predictive 'panic models' (dPAG-stimulation; DMH-inhibition; possibly conditioned suppression of drinking paradigms) also elicit and (indirectly) measure behaviors potentially related to flight. Models unrelated to flight (e.g. ultrasonic vocalization to conditioned stimuli); or for which flight elements may a relatively minor contributor to the behavior measured (Elevated T-maze) are less predictive of panicolytic or panicogenic action. These findings indicate that natural defensive behaviors provide a well-characterized pattern for analysis of effects of genetic or other physiological manipulations in the mouse, and may also serve as a model for analysis of defense-related human psychopathology.