Human amygdala activation during conditioned fear acquisition and extinction: a mixed-trial fMRI study

Effects of Seizures on Autonomic and Cardiovascular Function

Parial and generalized seizures often affect autonomic function during seizures as well as during the interictal and postictal periods. Activation or inhibition of areas in the central autonomic network can cause cardiovascular, gastrointestinal, cutaneous, pupillary, urinary, and genital manifestations. Autonomic dysfunction during or after seizures may cause cardiac and pulmonary changes that contribute to sudden unexplained death in epilepsy.

Effects of cannabidiol (CBD) on regional cerebral blood flow

Animal and human studies have suggested that cannabidiol (CBD) may possess anxiolytic properties, but how these effects are mediated centrally is unknown. The aim of the present study was to investigate this using functional neuroimaging. Regional cerebral blood flow (rCBF) was measured at rest using (99m)Tc-ECD SPECT in 10 healthy male volunteers, randomly divided into two groups of five subjects. Each subject was studied on two occasions, 1 week apart. In the first session, subjects were given an oral dose of CBD (400 mg) or placebo, in a double-blind procedure. SPECT images were acquired 90 min after drug ingestion. The Visual Analogue Mood Scale was applied to assess subjective states. In the second session, the same procedure was performed using the drug that had not been administered in the previous session. Within-subject between-condition rCBF comparisons were performed using statistical parametric mapping (SPM). CBD significantly decreased subjective anxiety and increased mental sedation, while placebo did not induce significant changes. Assessment of brain regions where anxiolytic effects of CBD were predicted a priori revealed two voxel clusters of significantly decreased ECD uptake in the CBD relative to the placebo condition (p<0.001, uncorrected for multiple comparisons). These included a medial temporal cluster encompassing the left amygdala-hippocampal complex, extending into the hypothalamus, and a second cluster in the left posterior cingulate gyrus. There was also a cluster of greater activity with CBD than placebo in the left parahippocampal gyrus (p<0.001). These results suggest that CBD has anxiolytic properties, and that these effects are mediated by an action on limbic and paralimbic brain areas.

Integrated technology for evaluation of brain function and neural plasticity

The study of neural plasticity has expanded rapidly in the past decades and has shown the remarkable ability of the developing, adult, and aging brain to be shaped by environmental inputs in health and after a lesion. Robust experimental evidence supports the hypothesis that neuronal aggregates adjacent to a lesion in the sensorimotor brain areas can take over progressively the function previously played by the damaged neurons. It definitely is accepted that such a reorganization modifies sensibly the interhemispheric differences in somatotopic organization of the sensorimotor cortices. This reorganization largely subtends clinical recovery of motor performances and sensorimotor integration after a stroke. Brain functional imaging studies show that recovery from hemiplegic strokes is associated with a marked reorganization of the activation patterns of specific brain structures. To regain hand motor control, the recovery process tends over time to bring the bilateral motor network activation toward a more normal intensity/extent, while overrecruiting simultaneously new areas, perhaps to sustain this process. Considerable intersubject variability exists in activation/hyperactivation pattern changes over time. Some patients display late-appearing dorsolateral prefrontal cortex activation, suggesting the development of "executive" strategies to compensate for the lost function. The AH in stroke often undergoes a significant "remodeling" of sensory and motor hand somatotopy outside the "normal" areas, or enlargement of the hand representation. The UH also undergoes reorganization, although to a lesser degree. Although absolute values of the investigated parameters fluctuate across subjects, secondary to individual anatomic variability, variation is minimal with regards to interhemispheric differences, due to the fact that individual morphometric characters are mirrored in the two hemispheres. Excessive interhemispheric asymmetry of the sensorimotor hand areas seems to be the parameter with highest sensitivity in describing brain reorganization after a monohemispheric lesion, and mapping motor and somatosensory cortical areas through focal TMS, fMRI, PET, EEG, and MEG is useful in studying hand representation and interhemispheric asymmetries in normal and pathologic conditions. TMS and MEG allow the detection of sensorimotor areas reshaping, as a result of either neuronal reorganization or recovery of the previously damaged neural network. These techniques have the advantage of high temporal resolution but also have limitations. TMS provides only bidimensional scalp maps, whereas MEG, even if giving three-dimensional mapping of generator sources, does so by means of inverse procedures that rely on the choice of a mathematical model of the head and the sources. These techniques do not test movement execution and sensorimotor integration as used in everyday life. fMRI and PET may provide the ideal means to integrate the findings obtained with the other two techniques. This multitechnology combined approach is at present the best way to test the presence and amount of plasticity phenomena underlying partial or total recovery of several functions, sensorimotor above all. Dynamic patterns of recovery are emerging progressively from the relevant literature. Enhanced recruitment of the affected cortex, be it spared perilesional tissue, as in the case of cortical stroke, or intact but deafferented cortex, as in subcortical strokes, seems to be the rule, a mechanism especially important in early postinsult stages. The transfer over time of preferential activation toward contralesional cortices, as observed in some cases, seems, however, to reflect a less efficient type of plastic reorganization, with some aspects of maladaptive plasticity. Reinforcing the use of the affected side can cause activation to increase again in the affected side with a corresponding enhancement of clinical function. Activation of the UH MI may represent recruitment of direct (uncrossed) corticospinal tracts and relate more to mirror movements, but it more likely reflects activity redistribution within preexisting bilateral, large-scale motor networks. Finally, activation of areas not normally engaged in the dysfunctional tasks, such as the dorsolateral prefrontal cortex or the superior parietal cortex in motor paralysis, might reflect the implication of compensatory cognitive strategies. An integrated approach with technologies able to investigate functional brain imaging is of considerable value in providing information on the excitability, extension, localization, and functional hierarchy of cortical brain areas. Deepening knowledge of the mechanisms regulating the long-term recovery (even if partial), observed for most neurologic sequelae after neural damage, might prompt newer and more efficacious therapeutic and rehabilitative strategies for neurologic diseases.

Neuroimaging correlates of anxiety after pediatric traumatic brain injury

BACKGROUND

Anxiety disorders are common after traumatic brain injury (TBI). Data on the neural correlates of these conditions are lacking. This study examines the relationship between brain damage, particularly to the orbitofrontal cortex (OFC) and temporal lobe, and anxiety symptoms and disorders.

METHODS

Ninety-five children and adolescents were followed for one year postinjury. Preinjury and one-year postinjury anxiety status were obtained from the parent. Magnetic resonance imaging was performed to evaluate brain lesions. The primary analysis used regression models to determine relationships between brain lesions and anxiety outcomes. As a secondary analysis, previously reported posttraumatic stress disorder (PTSD) data were reanalyzed using similar methods for purposes of comparison.

RESULTS

The primary analysis showed that greater volume and number of OFC lesions correlated with decreased risk for anxiety, whereas lesions in other brain areas did not correlate with anxiety. Consistent with prior data, the secondary analysis showed an inverse correlation between OFC damage and PTSD; temporal lobe damage was positively correlated with PTSD.

CONCLUSIONS

After pediatric TBI, greater damage to the OFC is associated with decreased risk for anxiety outcomes. Similar to adult data, these findings implicate OFC dysfunction in childhood anxiety. Temporal lobe damage did not correlate with anxiety, in contrast to the findings for PTSD.

Neural substrates mediating human delay and trace fear conditioning

Previous functional magnetic resonance imaging (fMRI) studies with human subjects have explored the neural substrates involved in forming associations in Pavlovian fear conditioning. Most of these studies used delay procedures, in which the conditioned stimulus (CS) and unconditioned stimulus (UCS) coterminate. Less is known about brain regions that support trace conditioning, a procedure in which an interval of time (trace interval) elapses between CS termination and UCS onset. Previous work suggests significant overlap in the neural circuitry supporting delay and trace fear conditioning, although trace conditioning requires recruitment of additional brain regions. In the present event-related fMRI study, skin conductance and continuous measures of UCS expectancy were recorded concurrently with whole-brain blood oxygenation level-dependent (BOLD) imaging during direct comparison of delay and trace discrimination learning. Significant activation was observed within the visual cortex for all CSs. Anterior cingulate and medial thalamic activity reflected associative learning common to both delay and trace procedures. Activations within the supplementary motor area (SMA), frontal operculum, middle frontal gyri, and inferior parietal lobule were specifically associated with trace interval processing. The hippocampus displayed BOLD signal increases early in training during all conditions; however, differences were observed in hippocampal response magnitude related to the accuracy of predicting UCS presentations. These results demonstrate overlapping patterns of activation within the anterior cingulate, medial thalamus, and visual cortex during delay and trace procedures, with additional recruitment of the hippocampus, SMA, frontal operculum, middle frontal gyrus, and inferior parietal lobule during trace conditioning. These data suggest that the hippocampus codes temporal information during trace conditioning, whereas brain regions supporting working memory processes maintain the CS-UCS representation during the trace interval.

Direct activation of the ventral striatum in anticipation of aversive stimuli

The brain "reward" system, centered on the limbic ventral striatum, plays a critical role in the response to pleasure and pain. The ventral striatum is activated in animal and human studies during anticipation of appetitive/pleasurable events, but its role in aversive/painful events is less clear. Here we present data from three human fMRI studies based on aversive conditioning using unpleasant cutaneous electrical stimulation and show that the ventral striatum is reliably activated. This activation is observed during anticipation and is not a consequence of relief after the aversive event. Further, the ventral striatum is activated in anticipation regardless of whether there is an opportunity to avoid the aversive stimulus or not. Our data suggest that the ventral striatum, a crucial element of the brain "reward" system, is directly activated in anticipation of aversive stimuli.

Evidence for preserved emotional memory in normal older persons

Emotion has been shown to have a modulatory effect on declarative memory. Normal aging is associated with a decline in declarative memory, but whether aging might affect the influence of emotion on memory has not been established. To investigate this, we administered a task that provides a detailed assessment of emotional memory to 80 neurologically normal adults ranging in age from 35 to 85 years. Across ages, memory performance was found to be modulated by the emotional significance of stimuli in a comparable manner (improved memory for gist, compromised memory for visual detail), despite an overall decline in memory performance with increasing age. The results raise the interesting possibility that aging has a differential effect on hippocampal versus amygdala function.

Stress impairs alpha(1A) adrenoceptor-mediated noradrenergic facilitation of GABAergic transmission in the basolateral amygdala

Intense or chronic stress can produce pathophysiological alterations in the systems involved in the stress response. The amygdala is a key component of the brain's neuronal network that processes and assigns emotional value to life's experiences, consolidates the memory of emotionally significant events, and organizes the behavioral response to these events. Clinical evidence indicates that certain stress-related affective disorders are associated with changes in the amygdala's excitability, implicating a possible dysfunction of the GABAergic system. An important modulator of the GABAergic synaptic transmission, and one that is also central to the stress response is norepinephrine (NE). In the present study, we examined the hypothesis that stress impairs the noradrenergic modulation of GABAergic transmission in the basolateral amygdala (BLA). In control rats, NE (10 microM) facilitated spontaneous, evoked, and miniature IPSCs in the presence of beta and alpha(2) adrenoceptor antagonists. The effects of NE were not blocked by alpha(1D) and alpha(1B) adrenoceptor antagonists, and were mimicked by the alpha(1A) agonist, A61603 (1 microM). In restrain/tail-shock stressed rats, NE or A61603 had no significant effects on GABAergic transmission. Thus, in the BLA, NE acting via presynaptic alpha(1A) adrenoceptors facilitates GABAergic inhibition, and this effect is severely impaired by stress. This is the first direct evidence of stress-induced impairment in the modulation of GABAergic synaptic transmission. The present findings provide an insight into possible mechanisms underlying the antiepileptogenic effects of NE in temporal lobe epilepsy, the hyperexcitability and hyper-responsiveness of the amygdala in certain stress-related affective disorders, and the stress-induced exacerbation of seizure activity in epileptic patients.

Amygdala and insular responses to emotionally valenced human faces in small animal specific phobia

BACKGROUND

Contemporary neurobiological models suggest that the amygdala plays an important role in the pathophysiology of anxiety disorders. However, it is not clear to what extent this concept applies across anxiety disorders. Several studies have examined brain function in specific phobias but did not demonstrate amygdala responses or use specific probes of the amygdala.

METHODS

Ten subjects with specific small animal phobia and 10 matched control subjects were studied with functional magnetic resonance imaging. Subjects viewed emotionally expressive and neutral faces, and amygdala blood oxygenation level dependent responses from each group were compared.

RESULTS

There was a significant response to the fearful versus neutral faces in the amygdala across both groups but no diagnosis x condition interaction. Post hoc analysis of the whole brain revealed a significantly greater response to the fearful versus neutral faces in the right insular cortex of the specific phobia group than in the control group.

CONCLUSIONS

Amygdala hyperresponsivity to emotional faces was not observed in subjects with small animal specific phobia, in contrast to findings in other anxiety disorders (e.g., posttraumatic stress disorder). This suggests a restricted role for the amygdala in specific phobia. The insular hyperresponsivity to fearful versus neutral faces in the subjects with specific phobias warrants further study.

Variations in maternal care alter GABA(A) receptor subunit expression in brain regions associated with fear

Maternal care influences the development of stress reactivity in the offspring. These effects are accompanied by changes in corticotropin-releasing factor (CRF) expression in brain regions that regulate responses to stress. However, such effects appear secondary to those involving systems that normally serve to inhibit CRF expression and release. Thus, maternal care over the first week of life alters GABA(A) (gamma-aminobutyric acid)(A) receptor mRNA subunit expression. The adult offspring of mothers that exhibit increased levels of pup licking/grooming and arched back-nursing (high LG-ABN mothers) show increased alpha1 mRNA levels in the medial prefrontal cortex, the hippocampus as well as the basolateral and central regions, of the amygdala and increased gamma2 mRNA in the amygdala. Western blot analyses confirm these effects at the level of protein. In contrast, the offspring of low LG-ABN mothers showed increased levels of alpha3 and alpha4 subunit mRNAs. The results of an adoption study showed that the biological offspring of low LG-ABN mothers fostered shortly after birth to high LG-ABN dams showed the increased levels of both alpha1 and gamma2 mRNA expression in the amygdala in comparison to peers fostered to other low LG-ABN mothers (the reverse was true for the biological offspring of high LG-ABN mothers). These findings are consistent with earlier reports of the effects of maternal care on GABA(A)/benzodiazepine receptor binding and suggest that maternal care can permanently alter the subunit composition of the GABA(A) receptor complex in brain regions that regulate responses to stress.

Neural components of social evaluation

Evaluative responses appear to involve 2 seemingly distinct sets of processes: those that are automatically activated and others that are more consciously controlled. Using functional magnetic resonance imaging, the authors investigated the brain systems associated with automatic and controlled evaluative processing. Participants made either evaluative (good-bad) or nonevaluative (past-present) judgments about famous names. Greater amygdala activity was observed for names rated as "bad" relative to those rated as "good," regardless of whether the task directly involved an evaluative judgment (good-bad) or not (past-present). Good-bad judgments resulted in greater medial and ventrolateral prefrontal cortex (PFC) activity than past-present judgments. Furthermore, there was greater ventrolateral PFC activity in good-bad judgments marked by greater ambivalence. Together, these findings indicate a neural distinction between processes engaged for automatic and controlled evaluation. Whereas automatic processes are sensitive to simple valence, controlled processes are sensitive to attitudinal complexity.

Neurobiology of emotion perception I: The neural basis of normal emotion perception

There is at present limited understanding of the neurobiological basis of the different processes underlying emotion perception. We have aimed to identify potential neural correlates of three processes suggested by appraisalist theories as important for emotion perception: 1) the identification of the emotional significance of a stimulus; 2) the production of an affective state in response to 1; and 3) the regulation of the affective state. In a critical review, we have examined findings from recent animal, human lesion, and functional neuroimaging studies. Findings from these studies indicate that these processes may be dependent upon the functioning of two neural systems: a ventral system, including the amygdala, insula, ventral striatum, and ventral regions of the anterior cingulate gyrus and prefrontal cortex, predominantly important for processes 1 and 2 and automatic regulation of emotional responses; and a dorsal system, including the hippocampus and dorsal regions of anterior cingulate gyrus and prefrontal cortex, predominantly important for process 3. We suggest that the extent to which a stimulus is identified as emotive and is associated with the production of an affective state may be dependent upon levels of activity within these two neural systems.

Amygdala and anterior cingulate cortex activation during affective startle modulation: a PET study of fear

The human startle response is modulated by emotional experiences, with startle potentiation associated with negative affect. We used positron emission tomography with 15O-water to study neural networks associated with startle modulation by phobic fear in a group of subjects with specific snake or spider phobia, but not both, during exposure to pictures of their feared and non-feared objects, paired and unpaired with acoustic startle stimuli. Measurement of eye electromyographic activity confirmed startle potentiation during the phobic as compared with the non-phobic condition. Employing a factorial design, we evaluated brain correlates of startle modulation as the interaction between startle and affect, using the double subtraction contrast (phobic startle vs. phobic alone) vs. (non-phobic startle vs. non-phobic alone). As a result of startle potentiation, a significant increase in regional cerebral blood flow was found in the left amygdaloid-hippocampal region, and medially in the affective division of the anterior cingulate cortex (ACC). These results provide evidence from functional brain imaging for a modulatory role of the amygdaloid complex on startle reactions in humans. They also point to the involvement of the affective ACC in the processing of startle stimuli during emotionally aversive experiences. The co-activation of these areas may reflect increased attention to fear-relevant stimuli. Thus, we suggest that the amygdaloid area and the ACC form part of a neural system dedicated to attention and orientation to danger, and that this network modulates startle during negative affect.

Encoding predictive reward value in human amygdala and orbitofrontal cortex

Adaptive behavior is optimized in organisms that maintain flexible representations of the value of sensory-predictive cues. To identify central representations of predictive reward value in humans, we used reinforcer devaluation while measuring neural activity with functional magnetic resonance imaging. We presented two arbitrary visual stimuli, both before and after olfactory devaluation, in a paradigm of appetitive conditioning. In amygdala and orbitofrontal cortex, responses evoked by a predictive target stimulus were decreased after devaluation, whereas responses to the nondevalued stimulus were maintained. Thus, differential activity in amygdala and orbitofrontal cortex encodes the current value of reward representations accessible to predictive cues.

Selection of voxel size and slice orientation for fMRI in the presence of susceptibility field gradients: application to imaging of the amygdala

The impact of voxel geometry on the blood oxygenation level-dependent (BOLD) signal detectability in the presence of field inhomogeneity is assessed and a quantitative approach to selecting appropriate voxel geometry is developed in this report. Application of the developed technique to BOLD sensitivity improvement of the human amygdala is presented. Field inhomogeneity was measured experimentally at 1.5 T and 3 T and the dominant susceptibility field gradient in the human amygdala was observed approximately along the superior-inferior direction. Based on the field mapping studies, an optimal selection for the slice orientation would be an oblique pseudo-coronal plane with its frequency-encoding direction parallel to the field gradient measured from each subject. Experimentally this was confirmed by comparing the normalized standard deviation of time-series echo-planar imaging signals acquired with different slice orientations, in the absence of a functional stimulus. A further confirmation with a carefully designed functional magnetic resonance imaging study is needed. Although the BOLD sensitivity may generally be improved by a voxel size commensurable with the activation volume, our quantitative analysis shows that the optimal voxel size also depends on the susceptibility field gradient and is usually smaller than the activation volume. The predicted phenomenon is confirmed with a hybrid simulation, in which the functional activation was mathematically added to the experimentally acquired rest-period echo-planar imaging data.

Lateralized impairment of the emotional enhancement of verbal memory in patients with amygdala-hippocampus lesion

This study investigated amygdala-hippocampus's functional asymmetry in the emotional modulation of memory for stories. Thirty-nine, right-handed, drug-resistant epilepsy patients who had been submitted to unilateral temporal lobectomy (19 left and 20 right) watched either an arousing or neutral version of a story presented audio-visually. The slide sequence was the same in the neutral and arousing version, the narratives were matched for structure and comprehensibility. The set and order of the 11 slide sequence were identical in both conditions. Free recall and recognition measures were taken 2h after story presentation. Subjects in the TLE group who watched the arousing version recalled more details than the subjects who watched the neutral version (t(37)=3.4,p<.001). The group who watched the arousing version recalled more details of the phase 2 of the story (t(37)=6.76,p<.001). Scores in both conditions did not differ between control subjects and temporal lobectomy patients. When the right and left lesioned groups' results were analyzed separately, it was observed that the two groups did not differ in their recall of the neutral version. The right lesioned group recalled more items of the arousal than the neutral version (Z=-3.55,p<.001). However the left lesioned group did not show the memory enhancement for the emotional version, in this group it was only found an enhanced recall of the more pictorial emotional segment of the narrative (Z=-3.11,p<.001). This illustrates that the right amygdala can influence retention of complex emotional stimuli with verbal and pictorial arousing properties. We concluded that an intact left amygdala-hippocampus is important for enhancement of memory related to emotionally arousing verbal material.

Sensing the invisible: differential sensitivity of visual cortex and amygdala to traumatic context

To what extent does emotional traumatic context affect sensory processing in the brain? A striking example of emotional impact on sensation is manifested in posttraumatic stress disorder (PTSD), in which a severe emotional trauma produces recurrent and vivid unpleasant sensory recollections. Here we report on an fMRI study exploring the sensory processing of trauma-related pictures in the visual cortex and amygdala in respect to PTSD. The impact of traumatic experience on brain responses was tested in relation to stimuli content and its level of recognition in a parametric factorial design. Twenty combat veterans, 10 with and 10 without PTSD, viewed backward-masked images of combat and noncombat content, presented at below, near, and above recognition thresholds. The response to combat content evoked more activation in the visual cortex in PTSD subjects than in non-PTSD subjects, only when images were presented at below recognition threshold. By contrast, the amygdala demonstrated increased activation in PTSD subjects irrespective of content and recognition threshold of the images. These intriguing findings are compatible with the notion that in PTSD, emotional traumatic experience could modify visual processing already at the preattentive level. On the other hand, lack of content specificity in the amygdala point to a possible predisposed mechanism for pathological processing of traumatic experience. The differential sensitivity of the amygdala and visual cortex to traumatic context implies distinct roles of limbic and sensory regions in the registration and recollection of emotional experience in the brain.

Neuropsychiatric and memory issues in epilepsy

Epilepsy is an extremely complex disorder characterized by marked variability in clinical presentation, etiology, diagnostic certainty, and therapeutic options. Neuropsychiatric and cognitive concomitant disorders are equally diverse and complex. Depression and anxiety, for example, may be preexisting conditions, occur only in peri-ictal or ictal states, or persist as constant interictal phenomena; both place additional burden on memory functions, which are further taxed by the effects of recurrent seizures, temporal lobe insult, and antiseizure medications. Such factors present considerable clinical challenges, particularly in outpatient settings. This article provides an overview of major psychiatric features of epilepsy and of issues regarding the nature of memory deficits in this neurologic population. The importance of identifying and treating potentially reversible causes of memory impairment and related forms of cognitive impairment is emphasized.

Differential amygdalar response to novel versus newly familiar neutral faces: a functional MRI probe developed for studying inhibited temperament

BACKGROUND

As a prelude to future studies of subjects with different temperaments, we sought to develop a probe to measure differential amygdalar responses to novel versus familiar stimuli. Prior neuroimaging studies of the amygdala in humans to date have focused principally on responses to emotional stimuli, primarily aversive, rather than to novelty per se.

METHODS

Eight normal subjects aged 22.4 +/- 1.3 years were scanned using functional magnetic resonance imaging (fMRI) during passive viewing of novel and familiar faces.

RESULTS

Using this newly developed paradigm, we found greater fMRI blood oxygenation level dependent (BOLD) signal response within the right amygdala to novel versus familiar faces--all with neutral expression. Furthermore, although a new facial identity was always presented in the novel condition, signal in the amygdala declined over time as it did for the familiar condition.

CONCLUSIONS

These results suggest that at least one primary function of the amygdala is to detect and process unexpected or unfamiliar events that have potential biological import, of which stimuli symbolic of fear or threat are but one possible example. We propose that this experimental paradigm will be useful for examining brain responses to novelty in different temperamental groups, as well as various psychiatric disorders.

Audition of laughing and crying leads to right amygdala activation in a low-noise fMRI setting

Adequate behavioral responses to socially relevant stimuli are often impaired after lesions of the amygdala. These impaired behavioral responses in particular concern the recognition of facial, and sometimes vocal, expressions of fear. Using low-noise functional magnetic resonance imaging (fMRI) in combination with controlled sound delivery, we investigated how the amygdala, insula and auditory cortex are involved in the processing of affective non-verbal vocalizations (laughing, crying) in healthy humans. The same samples of male and female laughing and crying were presented in two different experimental conditions: self-induction of the corresponding emotions while listening, and detection of artificial pitch shifts in the same stimuli. Both conditions led to bilateral activation of the amygdala, insula and auditory cortex with a right-hemisphere advantage in the amygdala, and larger activation during laughing than crying in the auditory cortex with a slight right-hemisphere advantage for laughing, both likely due to acoustic stimulus features. The results show that amygdala activation by emotionally meaningful sounds like laughing and crying is independent of the emotional involvement, suggesting the pattern recognition aspect of these sounds is crucial for this activation. This aspect was revealed by a low-noise fMRI protocol which presumably minimized confounding effects of stressful high-noise fMRI.

GABA-A and 5-HT1A receptor agonists block expression of fear-potentiated startle in mice

The present experiments characterized the acquisition of fear-potentiated startle (FPS) and determined the sensitivity of FPS to anxiolytic compounds in DBA/1J mice. A light (30 s) conditioned stimulus (CS) and mild footshock (0.14 mA, 0.5 s) unconditioned stimulus (US) were used. First, acquisition of FPS was examined by presenting the acoustic startle probe during and after each CS-US pairing trial, allowing for a trial-by-trial measurement of experience-dependent startle plasticity. In this novel protocol, mice showed robust acquisition (larger acoustic startle reflex in the presence of the CS) of FPS after as few as eight CS-US pairings. FPS was significantly greater when the CS and US were paired explicitly (light-paired) as compared to when both the US and CS were presented randomly (unpaired), or when the CS was presented alone (no shock), indicating pairing-dependent learning of the CS. Second, the present study assessed the sensitivity of FPS in mice to anxiolytic drugs. The GABA-A receptor agonists diazepam (3 and 6 mg/kg) and chlordiazepoxide (10 mg/kg) significantly reduced the expression of FPS post-training, as did the serotonin 1A receptor partial agonist buspirone (5 and 10 mg/kg). Furthermore, all three anxiolytic drugs reduced startle responding in a cue-specific manner and without significant changes in baseline responding. These data demonstrate a novel method of studying acquisition of FPS, and support the predictive validity of the FPS model of anxiolytic drug action in mice.

Role of the amygdala in decision-making

The somatic marker hypothesis proposes that both the amygdala and the orbitofrontal cortex are parts of a neural circuit critical for judgment and decision-making. Although both structures couple exteroceptive sensory information with interoceptive information concerning somatic/emotional states, they do so at different levels, thus making different contributions to the process. We define "primary inducers" as stimuli that unconditionally, or through learning (e.g., conditioning and semantic knowledge), can (perceptually or subliminally) produce states that are pleasurable or aversive. Encountering a fear object (e.g., a snake), a stimulus predictive of a snake, or semantic information such as winning or losing a large sum of money are all examples of primary inducers. "Secondary inducers" are entities generated by the recall of a personal or hypothetical emotional event or perceiving a primary inducer that generates "thoughts" and "memories" about the inducer, all of which, when they are brought to memory, elicit a somatic state. The episodic memory of encountering a snake, losing a large sum of money, imagining the gain of a large sum of money, or hearing or looking at primary inducers that bring to memory "thoughts" pertaining to an emotional event are all examples of secondary inducers. We present evidence in support of the hypothesis that the amygdala is a critical substrate in the neural system necessary for triggering somatic states from primary inducers. The ventromedial cortex is a critical substrate in the neural system necessary for the triggering of somatic states from secondary inducers. The amygdala system is a priori a necessary step for the normal development of the orbitofrontal system for triggering somatic states from secondary inducers. However, once this orbitofrontal system is developed, the induction of somatic states by secondary inducers via the orbitofrontal system is less dependent on the amygdala system. Perhaps the amygdala is equivalent to the hippocampus with regard to emotions, that is, necessary for acquiring new emotional attributes (anterograde emotions), but not for retrieving old emotional attributes (retrograde emotions). Given the numerous lesion and functional neuroimaging studies illustrating the involvement of the amygdala in complex cognitive and behavioral functions, including "social cognition," we suggest that this involvement is a manifestation of a more fundamental function mediated by the amygdala, which is to couple stimuli/entities with their emotional attributes, that is, the processing of somatic states from primary inducers.

Neuroimaging studies of amygdala function in anxiety disorders

Neuroimaging research has helped to advance neurobiological models of anxiety disorders. The amygdala is known to play an important role in normal fear conditioning and is implicated in the pathophysiology of anxiety disorders. The amygdala may also be a target for the beneficial effects of cognitive-behavioral and medication treatments for anxiety disorders. In the current paper, we review neuroimaging research pertaining to the role of the amygdala in anxiety disorders and their treatment. Moreover, we discuss the development of new neuroimaging paradigms for measuring aspects of amygdala function, as well as the function of related brain regions. We conclude that such tools hold great promise for facilitating progress in relevant basic neuroscience as well as clinical research domains.

The amygdalar circuit that acquires taste aversion memory differs from the circuit that extinguishes it

Experimental extinction is the decline in the frequency or intensity of a conditioned behaviour resulting from repetitive performance of the behaviour in the absence of the unconditioned stimulus or reinforcer (Pavlov, 1927). Ample behavioural evidence indicates that experimental extinction does not reflect unlearning of the original trace, but rather a relearning process, in which the new association of the conditioned stimulus with the absence of the original reinforcer comes to control behaviour (Rescorla, 1996). If experimental extinction is indeed learning rather than forgetting, are the neuronal circuits that subserve learning and extinction identical? We address this question by double dissociation analysis of the role of the central (CeA) and the basolateral (BLA) nuclei of the rat's amygdala in the acquisition and extinction, respectively, of conditioned taste aversion (CTA). Whereas local blockade of protein synthesis or beta-adrenergic receptors in the CeA blocks acquisition but not extinction of CTA, a similar intervention in the BLA blocks extinction but not acquisition. Hence, the amygdalar circuit that acquires taste aversion memory differs functionally from the circuit that extinguishes it.

Brain imaging studies in mood and anxiety disorders: special emphasis on the amygdala

Human studies attempting to elucidate brain functioning in health and disease are crucial for our understanding of neuropsychiatric disorders. In the past, scientists relied heavily on neurological lesion studies to understand the functional roles of brain areas. In the last few decades, brain imaging research has made it possible to investigate the molecular and synaptic neuronal events as well as the functioning of neuronal networks in vivo, in patients with neuropsychiatric illnesses. In this context, the functional role of the amygdala has been a focus of neuroimaging studies by leading researchers. Several of these researchers presented papers at a conference, entitled The Amygdala in Brain Function: Basic and Clinical Approaches, that provided the basis for this volume. These papers follow this review in the current volume. The present paper briefly summarizes the highlights of the different presentations, focusing on the functional diversity of the amygdala and its role in different neuropsychiatric disorders; reviews the various brain imaging technologies currently available; and discusses the major findings on the pathophysiology and treatment of depression, bipolar disorder, and anxiety disorders.

Amygdaloid regional cerebral blood flow and subjective fear during symptom provocation in anxiety disorders

Whether the amygdala is involved predominantly in emotional perception or in the generation of emotional states has been debated. We reviewed and reanalyzed data from our laboratory, indicating that subjective feelings of fear and distress are correlated with regional cerebral blood flow (rCBF) in the right but not the left amygdala during anxiety provocation in individuals with social anxiety disorder, specific phobias. and posttraumatic stress disorder. Positron emission tomography is a correlative technique, and casual inferences cannot be drawn. However, because studies demonstrate that treatment of social anxiety disorder with cognitive behavior therapy and selective serotonin reuptake inhibitors results in reduced rCBF in the amygdaloid complex and prospective studies reveal that treatment-induced alterations in amygdala rCBF can predict 1 year follow-up status in social anxiety disorder data support the notion that the amygdala, at least in part, seem casually involved in generating the subjective experience of fear.

Spatio-temporal dynamics of brain mechanisms in aversive classical conditioning: high-density event-related potential and brain electrical tomography analyses

Social cognition, including complex social judgments and attitudes, is shaped by individual learning experiences, where affect often plays a critical role. Aversive classical conditioning-a form of associative learning involving a relationship between a neutral event (conditioned stimulus, CS) and an aversive event (unconditioned stimulus, US)-represents a well-controlled paradigm to study how the acquisition of socially relevant knowledge influences behavior and the brain. Unraveling the temporal unfolding of brain mechanisms involved appears critical for an initial understanding about how social cognition operates. Here, 128-channel ERPs were recorded in 50 subjects during the acquisition phase of a differential aversive classical conditioning paradigm. The CS+ (two fearful faces) were paired 50% of the time with an aversive noise (CS upward arrow + /Paired), whereas in the remaining 50% they were not (CS upward arrow + /Unpaired); the CS- (two different fearful faces) were never paired with the noise. Scalp ERP analyses revealed differences between CS upward arrow + /Unpaired and CS- as early as approximately 120 ms post-stimulus. Tomographic source localization analyses revealed early activation modulated by the CS+ in the ventral visual pathway (e.g. fusiform gyrus, approximately 120 ms), right middle frontal gyrus (approximately 176 ms), and precuneus (approximately 240 ms). At approximately 120 ms, the CS- elicited increased activation in the left insula and left middle frontal gyrus. These findings not only confirm a critical role of prefrontal, insular, and precuneus regions in aversive conditioning, but they also suggest that biologically and socially salient information modulates activation at early stages of the information processing flow, and thus furnish initial insight about how affect and social judgments operate.

Age-related differences in brain activation during emotional face processing

Advancing age is associated with significant declines on neurobehavioral tasks that demand substantial mental effort. Functional imaging studies of mental abilities indicate that older adults faced with cognitive challenges tend to activate more regions, particularly frontal, than their younger counterparts, and that this recruitment of additional regions may reflect an attempt to compensate for inefficiency in cortical networks. The neural basis of emotion processing in aging has received little attention, and the goal of the present study was to use functional magnetic resonance imaging (fMRI) to examine the influence of age on facial emotion processing and activation in cortical and limbic regions. Participants (eight old and eight young adults) viewed facial displays of happiness, sadness, anger, fear, disgust, and neutrality in alternating blocks of emotion and age discrimination. We predicted that in response to an emotion discrimination task, older adults would demonstrate increased use of frontal regions relative to younger adults, perhaps combined with diminished use of regions recruited by younger adults, such as temporo-limbic regions. During the emotion discrimination task, young participants activated, visual, frontal and limbic regions, whereas older participants activated parietal, temporal and frontal regions. A direct comparison between emotion and age discrimination revealed that while younger adults activated the amygdala and surrounding temporo-limbic regions, older adults activated left frontal regions. The results of this study suggest that older adults may rely on different cortical networks to perceive emotional facial expressions than do their younger counterparts.

Hippocampal place cells acquire location-specific responses to the conditioned stimulus during auditory fear conditioning

We recorded neurons from the hippocampus of freely behaving rats during an auditory fear conditioning task. Rats received either paired or unpaired presentations of an auditory conditioned stimulus (CS) and an electric shock unconditioned stimulus (US). Hippocampal neurons (place and theta cells) acquired responses to the auditory CS in the paired but not in the unpaired group. After CS-US pairing, rhythmic firing of theta cells became synchronized to the onset of the CS. Conditioned responses of place cells were gated by their location-specific firing, so that after CS-US pairing, place cells responded to the CS only when the rat was within the cell's place field. These findings may help to elucidate how the hippocampus contributes to context-specific memory formation during associative learning.

Working memory and fear conditioning

Previous studies of associative learning implicate higher-level cognitive processes in some forms of classical conditioning. An ongoing debate is concerned with the extent to which attention and awareness are necessary for trace but not delay eye-blink conditioning [Clark, R. E. & Squire, L. R. (1998) Science 280, 77-81; Lovibond, P. F. & Shanks, D. (2002) J. Exp. Psychol. Anim. Behav. Processes 28, 38-42]. In trace conditioning, a short interval is interposed between the termination of the conditioned stimulus (CS) and the onset of the unconditioned stimulus (US). In delay conditioning, the CS and US overlap. We here investigate the extent to which human classical fear conditioning depends on working memory. Subjects had to carry out an n-back task, requiring tracking an item 1 or 2 back in a sequentially presented list of numbers, while simultaneously being tested for their ability to associate auditory cues with shocks under a variety of conditions (single-cue versus differential; delay versus trace; no task versus 0-, 1-, and 2-back). Differential delay conditioning proved to be more resilient than differential trace conditioning but does show a reduction due to task interference similar in slope to that found in trace conditioning. Explicit knowledge of the stimulus contingency facilitates but does not guarantee trace conditioning. Only the single-cue delay protocol shows conditioning during the more difficult working memory task. Our findings suggest that the larger the cognitive demands on the system, the less likely conditioning occurs. A postexperimental questionnaire showed a positive correlation between conditioning and awareness for differential trace conditioning extinction.

Functional MRI of human amygdala activity during Pavlovian fear conditioning: stimulus processing versus response expression

Although laboratory animal studies have shown that the amygdala plays multiple roles in conditional fear, less is known about the human amygdala. Human subjects were trained in a Pavlovian fear conditioning paradigm during functional magnetic resonance imaging (fMRI). Brain activity maps correlated with reference waveforms representing the temporal pattern of visual conditional stimuli (CSs) and subject-derived autonomic responses were compared. Subjects receiving paired CS-shock presentations showed greater amygdala activity than subjects receiving unpaired CS-shock presentations when their brain activity was correlated with a waveform generated from their behavioral responses. Stimulus-based waveforms revealed learning differences in the visual cortex, but not in the amygdala. These data support the view that the amygdala is important for the expression of learned behavioral responses during Pavlovian fear conditioning.

Appetitive and aversive olfactory learning in humans studied using event-related functional magnetic resonance imaging

We combined event-related functional magnetic resonance imaging (fMRI) with olfactory classical conditioning to differentiate the neural responses evoked during appetitive and aversive olfactory learning. Three neutral faces [the conditioned stimuli (CS+)] were repetitively paired with pleasant, neutral, or unpleasant odors [the unconditioned stimuli (UCS)] in a partial reinforcement schedule. A fourth face was never paired to odor [the nonconditioned stimulus (CS-)]. Learning-related neural activity, comparing unpaired (face only) CS+ stimuli with CS-, showed valence-independent activations in rostral and caudal orbitofrontal cortex (OFC). Medial OFC responded to the appetitive (app) CS+, whereas lateral OFC responded to the aversive (av) CS+. Within nucleus accumbens, neural responses showed divergent activation profiles that increased with time in response to the appCS+ but decreased in response to the avCS+. In posterior amygdala, responses were elicited by the appCS+, which habituated over time. In temporal piriform cortex, neural responses were evoked by the avCS+, which progressively increased with time. These results highlight regional and temporal dissociations during olfactory learning and imply that emotionally salient odors can engender cross-modal associative learning. Moreover, the findings suggest that the role of human primary (piriform) and secondary olfactory cortices transcends their function as mere intermediaries of chemosensory information processing.

Affective analgesia following the administration of morphine into the amygdala of rats

The amygdala processes stimuli that threaten the individual and organizes the execution of affective behaviors that permit the individual to cope with the threat. The prototypical threat to an individual is exposure to a noxious stimulus. The present study evaluated the contribution of the amygdala in modulating the affective response of rats to noxious stimulation. Vocalization afterdischarges (VADs) are a validated model of the affective response of rats to noxious tailshock. The antinociceptive action of morphine microinjected into the amygdala on VAD thresholds was compared to its effect on the thresholds of other tailshock-elicited responses (vocalizations during shock, VDS and spinal motor reflexes, SMRs). Whereas VADs are organized within the forebrain, VDSs and SMRs are organized at medullary and spinal levels of the neuraxis, respectively. The bilateral administration of morphine into the basolateral complex of the amygdala (BLC) produced dose-dependent increases in VAD and VDS thresholds, although increases in VAD thresholds were significantly greater than increases in VDS thresholds. Administration of morphine into BLC was ineffective in elevating SMR thresholds. Morphine-induced increases in vocalization thresholds were reversed in a dose-dependent manner by microinjection of the opiate receptor antagonist methylnaloxonium into BLC. Microinjection of morphine in the vicinity to the BLC did not alter vocalization thresholds. The present results provide further evidence for the preferential involvement of the amygdala in modulation of the affective component of the pain experience.

Conflicting processes in the extinction of conditioned taste aversion: behavioral and molecular aspects of latency, apparent stagnation, and spontaneous recovery

The study of experimental extinction and of the spontaneous recovery of the extinguished memory could cast light on neurobiological mechanisms by which internal representations compete to control behavior. In this work, we use a combination of behavioral and molecular methods to dissect subprocesses of experimental extinction of conditioned taste aversion (CTA). Extinction of CTA becomes apparent only 90 min after the extinction trial. This latency is insensitive to muscarinic and beta-adrenergic modulation and to protein synthesis inhibition in the insular cortex (IC). Immediately afterwards, however, the extinguishing trace becomes sensitive to beta-adrenergic blockade and protein synthesis inhibition. The subsequent kinetics and magnitude of extinction depend on whether a spaced or massed extinction protocol is used. A massed protocol is highly effective in the short run, but results in apparent stagnation of extinction in the long-run, which conceals fast spontaneous recovery of the preextinguished trace. This recovery can be truncated by a beta-adrenergic agonist or a cAMP analog in the insular cortex, suggesting that spontaneous overtaking of the behavioral control by the original association is regulated at least in part by beta-adrenergic input, probably operating via the cAMP cascade, long after the offset of the conditioned stimulus. Hence, the performance of the subject in experimental extinction is the sum total of multiple, sometimes conflicting, time-dependent processes.

The human amygdala and the emotional evaluation of sensory stimuli

A wealth of animal data implicates the amygdala in aspects of emotional processing. In recent years, functional neuroimaging and neuropsychological studies have begun to refine our understanding of the functions of the amygdala in humans. This literature offers insights into the types of stimuli that engage the amygdala and the functional consequences that result from this engagement. Specific conclusions and hypotheses include: (1) the amygdala activates during exposure to aversive stimuli from multiple sensory modalities; (2) the amygdala responds to positively valenced stimuli, but these responses are less consistent than those induced by aversive stimuli; (3) amygdala responses are modulated by the arousal level, hedonic strength or current motivational value of stimuli; (4) amygdala responses are subject to rapid habituation; (5) the temporal characteristics of amygdala responses vary across stimulus categories and subject populations; (6) emotionally valenced stimuli need not reach conscious awareness to engage amygdala processing; (7) conscious hedonic appraisals do not require amygdala activation; (8) activation of the amygdala is associated with modulation of motor readiness, autonomic functions, and cognitive processes including attention and memory; (9) amygdala activations do not conform to traditional models of the lateralization of emotion; and (10) the extent and laterality of amygdala activations are related to factors including psychiatric status, gender and personality. The strengths and weakness of these hypotheses and conclusions are discussed with reference to the animal literature.

The emerging dialogue between psychoanalysis and neuroscience: neuroimaging perspectives

Current progress in the cognitive neurosciences is highly relevant to the development of psychoanalytic theory and practice. Neuroscience is today becoming mature enough to provide empirical biological approaches for the investigation of psychoanalytic models and observations. The current state of functional neuroimaging techniques is reviewed, selected paradigms and findings relevant to psychotherapy research are presented, and ways to pursue the dialogue between psychoanalysts and neuroscientists are discussed, as are some related obstacles and pitfalls. The emerging dialogue between psychoanalysts and neuroscientists may help not only to reestablish a solid position of psychodynamic theory and treatment in contemporary medicine, but also to bridge the division between "psychological" and "somatic" treatments, and gain important insights into the mind-brain relationship.

Exposure to a retrieval cue in rats induces changes in regional brain glucose metabolism in the amygdala and other related brain structures

Pre-test exposure to training-related cues is known to improve subsequent retention performance. To identify brain regions engaged in processes promoted by retrieval cues, a brain imaging approach using the [6-14C]glucose autoradiographic technique was used. Sprague-Dawley rats trained in a brightness discrimination avoidance task were submitted to different cueing conditions after a 1- or a 21-day training-to-test interval (TTI). Animals were either non-cued, cued with a box, or cued with a box and the light that served as a discriminative stimulus. Effects of the different cueing conditions on retention performance or on metabolic activity in 58 different brain regions were investigated. Rats cued with the light exhibited a subsequent improvement of their retention performance relative to controls, when tested at the 1- but not 21-days TTI, confirming our previous results. At the 1-day retention interval, a comparison between rats cued with the box and rats cued with the box and the light showed that the light cue significantly increased glucose uptake in a neuronal network composed of the lateral, basal, and central nuclei of the amygdala, the anterior and suprachiasmatic hypothalamic nuclei, the nucleus accumbens, the medial septum, and the insular cortex. In contrast, at the 21-day retention interval, both groups demonstrated similar cerebral metabolic activity. The present results indicate that exposure to a light cue increased metabolic activity in the previously mentioned brain structures only when the light acted as an effective retrieval cue, suggesting an involvement of this network in the processes triggered by a retrieval cue. Arguments are provided supporting the notion that the amygdala may play a key role in these processes. Whether the amygdala is a part of a neural network involved in retrieval processes or in neuromodulating systems that favour the efficacy of retrieval processes is also discussed.

Human models as tools in the development of psychotropic drugs

Despite the growing means devoted to research and development (R α D) and refinements in the preclinical stages, the efficiency of central nervous system (CMS) drug development is disappointing. Many drugs reach patient studies with an erroneous therapeutic indication andlor in incorrect doses. Apart from the first clinical studies, which are conducted in healthy volunteers and focus only on safety, iolerability, and pharmacokinetics, drug development mostly relies on patient studies. Psychiatric disorders are characterized by heterogeneity and a high rate of comorbidity. It is becoming increasingly difficult to recruit patients for clinical trials and there are many confounding factors in this population, for example, those related to treatments. In order to keep patient exposure and financial expenditure to a minimum, it is important to avoid ill-designed and inconclusive studies. This risk could be minimized by gathering pharmacodynamic data earlier in development and considering that the goal of a phase 1 plan is to reach patient studies with clear ideas about the compound's pharmacodynamic profile, its efficacy in the putative indication (proof of concept), and pharmacokinetic/pharmacodynamic relationships, in addition to safety, tolerability, and pharmacokinetics. Human models in healthy volunteers may be useful tools for this purpose, but their use necessitates a global adaptation of the phase scheme, favoring pharmacodynamic assessments without neglecting safety. We are engaged in an R α D program aimed to adapt existing models and develop new paradigms suitable for early proof of concept substantiation.

Neural response to emotional faces with and without awareness: event-related fMRI in a parietal patient with visual extinction and spatial neglect

This study examined whether differential neural responses are evoked by emotional stimuli with and without conscious perception, in a patient with visual neglect and extinction. Stimuli were briefly shown in either right, left, or both fields during event-related fMRI. On bilateral trials, either a fearful or neutral left face appeared with a right house, and it could either be extinguished from awareness or perceived. Seen faces in left visual field (LVF) activated primary visual cortex in the damaged right-hemisphere and bilateral fusiform gyri. Extinguished left faces increased activity in striate and extrastriate cortex, compared with right houses only. Critically, fearful faces activated the left amygdala and extrastriate cortex both when seen and when extinguished; as well as bilateral orbitofrontal and intact right superior parietal areas. Comparison of perceived versus extinguished faces revealed no difference in amygdala for fearful faces. Conscious perception increased activity in fusiform, parietal and prefrontal areas of the left-hemisphere, irrespective of emotional expression; while a differential emotional response to fearful faces occurring specifically with awareness was found in bilateral parietal, temporal, and frontal areas. These results demonstrate that amygdala and orbitofrontal cortex can be activated by emotional stimuli even without awareness after parietal damage; and that substantial unconscious residual processing can occur within spared brain areas well beyond visual cortex, despite neglect and extinction.

Circuits and systems in stress. II. Applications to neurobiology and treatment in posttraumatic stress disorder

This paper follows the preclinical work on the effects of stress on neurobiological and neuroendocrine systems and provides a comprehensive working model for understanding the pathophysiology of posttraumatic stress disorder (PTSD). Studies of the neurobiology of PTSD in clinical populations are reviewed. Specific brain areas that play an important role in a variety of types of memory are also preferentially affected by stress, including hippocampus, amygdala, medial prefrontal cortex, and cingulate. This review indicates the involvement of these brain systems in the stress response, and in learning and memory. Affected systems in the neural circuitry of PTSD are reviewed (hypothalamic-pituitary-adrenal axis (HPA-axis), catecholaminergic and serotonergic systems, endogenous benzodiazepines, neuropeptides, hypothalamic-pituitary-thyroid axis (HPT-axis), and neuro-immunological alterations) as well as changes found with structural and functional neuroimaging methods. Converging evidence has emphasized the role of early-life trauma in the development of PTSD and other trauma-related disorders. Current and new targets for systems that play a role in the neural circuitry of PTSD are discussed. This material provides a basis for understanding the psychopathology of stress-related disorders, in particular PTSD.

Electrophysiological responses in the human amygdala discriminate emotion categories of complex visual stimuli

The human amygdala has been shown to participate in processing emotionally salient stimuli related to threat, danger, and aversion, data that have come primarily from functional imaging and lesion studies. Recording intracranial field potentials from five amygdalas in four patients with chronically implanted depth electrodes, we analyzed responses in the gamma frequency range, a region of the power spectrum thought to reflect especially the contribution of neuronal activity to cognitive processes. Significant changes in the power amplitude of responses were obtained selectively to visual images judged to look aversive but not to those judged to look pleasant or neutral. Several possible confounds were addressed: all four patients had been carefully selected so that the amygdalas from which recordings were obtained were distal to epileptogenic foci, making it likely that we recorded from healthy tissue, and the observed responses could not be attributed to luminance or color differences between the stimuli. A further analysis of differences in power between the high and low gamma bands revealed an additional structure that discriminated those stimuli related to bodily injury from those related to disgust. Despite the increased power amplitude in the gamma range, there was no stimulus-locked phase coherence. The observed responses in the gamma frequency range may reflect the role of the amygdala in binding perceptual representations of the stimuli with memory, emotional response, and modulation of ongoing cognition, on the basis of the emotional significance of the stimuli.

Phobias and preparedness: the selective, automatic, and encapsulated nature of fear

We describe evidence for an evolved module for fear elicitation and fear learning with four primary characteristics. First, it is preferentially activated by stimuli related to survival threats in evolutionary history. Thus, fear-relevant stimuli lead to superior conditioning of aversive associations compared with fear-irrelevant stimuli. Second, the module is automatically activated by fear-relevant stimuli, meaning that fear activation occurs before conscious cognitive analysis of the stimulus can occur. Third, the fear module is relatively impenetrable to conscious cognitive control, and fear conditioning with fear-relevant stimuli can occur even with subliminal conditioned stimuli. Fourth, the amygdala seems to be the central brain area dedicated to the fear module. Finally, we propose that there are two levels of fear conditioning, with an emotional level that is relatively independent of the cognitive contingency level, each mediated by different brain areas.

Emotion, cognition, and behavior

Emotion is central to the quality and range of everyday human experience. The neurobiological substrates of human emotion are now attracting increasing interest within the neurosciences motivated, to a considerable extent, by advances in functional neuroimaging techniques. An emerging theme is the question of how emotion interacts with and influences other domains of cognition, in particular attention, memory, and reasoning. The psychological consequences and mechanisms underlying the emotional modulation of cognition provide the focus of this article.

Cerebellar responses during anticipation of noxious stimuli in subjects recovered from depression. Functional magnetic resonance imaging study

BACKGROUND

Subjects recovered from depression have a substantial risk for recurrence of depression, suggesting persistent abnormalities in brain activity.

AIMS

To test whether women recovered from depression show abnormal brain activity in functional magnetic resonance imaging (fMRI) during a conditioning paradigm with a noxious pain stimulus.

METHOD

Ten unmedicated women who had recovered from major depression and eight healthy control women each received either noxious hot or non-noxious warm stimuli, the onset of which was signalled by a specific coloured light during 3-tesla echo planar imaging-based fMRI.

RESULTS

Similar patterns of brain activation were found during painful stimulation for both patients and healthy controls. However, relative to healthy controls, subjects recovered from depression showed a reduced response in the cerebellum during anticipation of the noxious stimulus compared with anticipation of the non-noxious stimulus.

CONCLUSIONS

Our data suggest that abnormal cerebellar function could be a marker of vulnerability to recurrent depression. This could provide a new target for therapeutic interventions.

Impaired fear conditioning in Alzheimer's disease

Classical conditioning of the fear response is a basic form of nondeclarative (nonconscious) memory that mediates both normal and pathological responses to aversive stimuli. Because fear conditioning critically depends on the amygdala, a medial temporal lobe structure that frequently undergoes significant pathological changes early in the course of Alzheimer's disease (AD), we hypothesized that fear conditioning would be impaired in patients with mild to moderate AD. We examined simple classical fear conditioning in a group of 10 patients with probable AD and 14 demographically matched, neurologically intact elderly controls. During conditioning, one stimulus (e.g. a green rectangle, the conditioned stimulus (CS+)), was paired with an aversive stimulus (a loud noise, the unconditioned stimulus (US)) using a partial reinforcement conditioning schedule. The opponent color (e.g. red rectangle), the CS-, was never paired with the US. The elderly controls acquired robust fear responses as demonstrated by their differential skin-conductance responses to the CS+ and CS-. In contrast, the AD group showed a marked impairment in conditioning, failing to exhibit significant conditioned fear responses. This failure to acquire conditioned responses could not be attributed to diminished responding by patients, relative to controls, to the aversive US. The results indicate that fear conditioning, an amygdala-dependent form of memory, is impaired in AD. These findings complement previous reports of impairments in declarative emotional memory in AD by demonstrating that a basic form of nondeclarative emotional memory is also impaired in AD.

Right-sided human prefrontal brain activation during acquisition of conditioned fear

This H2(15)O positron emission tomography (PET) study reports on relative regional cerebral blood flow (rCBF) alterations during fear conditioning in humans. In the PET scanner, subjects viewed a TV screen with either visual white noise or snake videotapes displayed alone, then with electric shocks, followed by final presentations of white noise and snakes. Autonomic nervous system responses confirmed fear conditioning only to snakes. To reveal neural activation during acquisition, while equating sensory stimulation, scans during snakes with shocks and white noise alone were contrasted against white noise with shocks and snakes alone. During acquisition, rCBF increased in the right medial frontal gyrus, supporting a role for the prefrontal cortex in fear conditioning to unmasked evolutionary fear-relevant stimuli.