Hemodynamic responses of the amygdala, the orbitofrontal cortex and the visual cortex during a fear conditioning paradigm

Electrocortical activity associated with movement-related fear: a methodological exploration of a threat-conditioning paradigm involving destabilising perturbations during quiet standing

Musculoskeletal trauma often leads to lasting psychological impacts stemming from concerns of future injuries. Often referred to as kinesiophobia or re-injury anxiety, such concerns have been shown to hinder return to physical activity and are believed to increase the risk for secondary injuries. Screening for re-injury anxiety is currently restricted to subjective questionnaires, which are prone to self-report bias. We introduce a novel approach to objectively identify electrocortical activity associated with the threat of destabilising perturbations. We aimed to explore its feasibility among non-injured persons, with potential future implementation for screening of re-injury anxiety. Twenty-three participants stood blindfolded on a translational balance perturbation platform. Consecutive auditory stimuli were provided as low (neutral stimulus [CS-]) or high (conditioned stimulus [CS+]) tones. For the main experimental protocol (Protocol I), half of the high tones were followed by a perturbation in one of eight unpredictable directions. A separate validation protocol (Protocol II) requiring voluntary squatting without perturbations was performed with 12 participants. Event-related potentials (ERP) were computed from electroencephalography recordings and significant time-domain components were detected using an interval-wise testing procedure. High-amplitude early contingent negative variation (CNV) waves were significantly greater for CS+ compared with CS- trials in all channels for Protocol I (> 521-800ms), most prominently over frontal and central midline locations (P ≤ 0.001). For Protocol II, shorter frontal ERP components were observed (541-609ms). Our test paradigm revealed electrocortical activation possibly associated with movement-related fear. Exploring the discriminative validity of the paradigm among individuals with and without self-reported re-injury anxiety is warranted.

Conscious expectancy rather than associative strength elicits brain activity during single-cue fear conditioning

The neurocognitive processes underlying Pavlovian conditioning in humans are still largely debated. The conventional view is that conditioned responses (CRs) emerge automatically as a function of the contingencies between a conditioned stimulus (CS) and an unconditioned stimulus (US). As such, the associative strength model asserts that the frequency or amplitude of CRs reflects the strength of the CS-US associations. Alternatively, the expectation model asserts that the presentation of the CS triggers conscious expectancy of the US, which is responsible for the production of CRs. The present study tested the hypothesis that there are dissociable brain networks related to the expectancy and associative strength theories using a single-cue fear conditioning paradigm with a pseudo-random intermittent reinforcement schedule during functional magnetic resonance imaging. Participants' (n = 21) trial-by-trial expectations of receiving shock displayed a significant linear effect consistent with the expectation model. We also found a positive linear relationship between the expectancy model and activity in frontoparietal brain areas including the dorsolateral prefrontal cortex (PFC) and dorsomedial PFC. While an exploratory analysis found a linear relationship consistent with the associated strength model in the insula and early visual cortex, our primary results are consistent with the view that conscious expectancy contributes to CRs.

Effects of fearful face presentation time and observer's eye movement on the gaze cue effect

BACKGROUND

There are many conflicting findings on the gaze cueing effect (GCE) of emotional facial expressions. This study aimed to investigate whether an averted gaze, accompanied by a fearful expression of different durations, could enhance attentional orientation, as measured by a participant's eye movements.

METHODS

Twelve participants (3 females) completed the gaze cue task, reacting to a target location after observing changes in the gaze and expression of a face illustrated on a computer screen. Meanwhile, participants' eye movements were monitored by electrooculography. The GCE was calculated by reaction time as an indicator of attention shift.

RESULTS

The analysis of the overall data did not find a significant effect of fearful facial expressions on the GCE. However, analysis of trial data that excluded a participant's eye movement data showed that brief (0, 100 ms) presentation of the fearful facial expression enhanced the GCE compared to that during a neutral facial expression, although when the presentation time of the fearful expression was increased to 200 or 400 ms, the GCE of the fearful expression was at the same level as when model showed a neutral expression.

CONCLUSIONS

The results suggest that the attention-enhancing effect of gaze cues induced by rapidly presented fearful expressions occurs only when the effect of eye movement trials is excluded. This effect may be mediated by reflexively neural circuits in the amygdala that process threatening stimuli. However, as the expression duration increased, the fearful expression's attention-enhancing effect decreased. We suggest that future studies on the emotion modulation of GCE should consider the negative effects of participants' saccades and blinks on the experimental results.

Brain responses in aggression-prone individuals: A systematic review and meta-analysis of functional magnetic resonance imaging (fMRI) studies of anger- and aggression-eliciting tasks

Reactive aggression in response to perceived threat or provocation is part of humans' adaptive behavioral repertoire. However, high levels of aggression can lead to the violation of social and legal norms. Understanding brain function in individuals with high levels of aggression as they process anger- and aggression-eliciting stimuli is critical for refining explanatory models of aggression and thereby improving interventions. Three neurobiological models of reactive aggression - the limbic hyperactivity, prefrontal hypoactivity, and dysregulated limbic-prefrontal connectivity models - have been proposed. However, these models are based on neuroimaging studies involving mainly non-aggressive individuals, leaving it unclear which model best describes brain function in those with a history of aggression. We conducted a systematic literature search (PubMed and Psycinfo) and Multilevel Kernel Density meta-analysis (MKDA) of nine functional magnetic resonance imaging (fMRI) studies (eight included in the between-group analysis [i.e., aggression vs. control groups], five in the within-group analysis). Studies examined brain responses to tasks putatively eliciting anger and aggression in individuals with a history of aggression alone and relative to controls. Individuals with a history of aggression exhibited greater activity in the superior temporal gyrus and in regions comprising the cognitive control and default mode networks (right posterior cingulate cortex, precentral gyrus, precuneus, right inferior frontal gyrus) during reactive aggression relative to baseline conditions. Compared to controls, individuals with a history of aggression exhibited increased activity in limbic regions (left hippocampus, left amygdala, left parahippocampal gyrus) and temporal regions (superior, middle, inferior temporal gyrus), and reduced activity in occipital regions (left occipital cortex, left calcarine cortex). These findings lend support to the limbic hyperactivity model in individuals with a history of aggression, and further indicate altered temporal and occipital activity in anger- and aggression-eliciting conditions involving face and speech processing.

Altered dynamic brain activity and its association with memory decline after night shift-related sleep deprivation in nurses

AIMS AND OBJECTIVES

To investigate, for the first time, aberrant time-varying local brain activity in nurses following night shift-related sleep deprivation (SD) and its association with memory decline.

BACKGROUND

Prior studies have elucidated alterations in static local brain activity resulting from SD in the occupations outside medical profession.

DESIGN

A longitudinal study followed the STROBE recommendations.

METHODS

Twenty female nurses underwent resting-state functional magnetic resonance imaging and memory function assessment (by Complex Figure Test (CFT) and the California Verbal Learning Test, Second Edition (CVLT-II)) twice, once in a rested wakefulness (RW) state and another after SD. By combining the sliding-window approach and amplitude of low-frequency fluctuation (ALFF) analysis, the dynamic ALFF (dALFF) variability was calculated to reflect the characteristics of dynamic local brain activity.

RESULTS

Poor performance on the CFT and CVLT-II was observed in nurses with night shift-related SD. Reduced dALFF variability was found in a set of cognition-related brain regions (including the medial/middle/superior frontal gyrus, anterior/posterior cingulate gyrus, precuneus, angular gyrus, orbitofrontal and subgenual areas, and posterior cerebellum lobe), while increased dALFF variability was observed in the somatosensory-related, visual and auditory regions. SD-related dALFF variability alterations correlated with changes in subjects' performance on the CFT and CVLT-II.

CONCLUSIONS

Night shift-related SD disturbed dynamic brain activity in high cognitive regions and induced compensatory reactions in primary perceptual cortex. Identifying dALFF variability abnormalities may broaden our understanding of neural substrates underlying SD-related cognitive alterations, especially memory dysfunction.

RELEVANCE TO CLINICAL PRACTICE

Night shift-related SD is as an important occupational hazard affecting brain function in nurses. The effective countermeasure addressing the adverse outcomes of SD should be advocated for nurses.

PATIENT OR PUBLIC CONTRIBUTION

Patients or public were not involved in the design and implementation of the study or the analysis and interpretation of the data.

Mental imagery can generate and regulate acquired differential fear conditioned reactivity

Mental imagery is an important tool in the cognitive control of emotion. The present study tests the prediction that visual imagery can generate and regulate differential fear conditioning via the activation and prioritization of stimulus representations in early visual cortices. We combined differential fear conditioning with manipulations of viewing and imagining basic visual stimuli in humans. We discovered that mental imagery of a fear-conditioned stimulus compared to imagery of a safe conditioned stimulus generated a significantly greater conditioned response as measured by self-reported fear, the skin conductance response, and right anterior insula activity (experiment 1). Moreover, mental imagery effectively down- and up-regulated the fear conditioned responses (experiment 2). Multivariate classification using the functional magnetic resonance imaging data from retinotopically defined early visual regions revealed significant decoding of the imagined stimuli in V2 and V3 (experiment 1) but significantly reduced decoding in these regions during imagery-based regulation (experiment 2). Together, the present findings indicate that mental imagery can generate and regulate a differential fear conditioned response via mechanisms of the depictive theory of imagery and the biased-competition theory of attention. These findings also highlight the potential importance of mental imagery in the manifestation and treatment of psychological illnesses.

Imaging of Functional Brain Circuits during Acquisition and Memory Retrieval in an Aversive Feedback Learning Task: Single Photon Emission Computed Tomography of Regional Cerebral Blood Flow in Freely Behaving Rats

Active avoidance learning is a complex form of aversive feedback learning that in humans and other animals is essential for actively coping with unpleasant, aversive, or dangerous situations. Since the functional circuits involved in two-way avoidance (TWA) learning have not yet been entirely identified, the aim of this study was to obtain an overall picture of the brain circuits that are involved in active avoidance learning. In order to obtain a longitudinal assessment of activation patterns in the brain of freely behaving rats during different stages of learning, we applied single-photon emission computed tomography (SPECT). We were able to identify distinct prefrontal cortical, sensory, and limbic circuits that were specifically recruited during the acquisition and retrieval phases of the two-way avoidance learning task.

Neural substrates of appetitive and aversive prediction error

Prediction error, defined by the discrepancy between real and expected outcomes, lies at the core of associative learning. Behavioural investigations have provided evidence that prediction error up- and down-regulates associative relationships, and allocates attention to stimuli to enable learning. These behavioural advances have recently been followed by investigations into the neurobiological substrates of prediction error. In the present paper, we review neuroscience data obtained using causal and recording neural methods from a variety of key behavioural designs. We explore the neurobiology of both appetitive (reward) and aversive (fear) prediction error with a focus on the mesolimbic dopamine system, the amygdala, ventrolateral periaqueductal gray, hippocampus, cortex and locus coeruleus noradrenaline. New questions and avenues for research are considered.

Cannabinoid modulation of corticolimbic activation to threat in trauma-exposed adults: a preliminary study

RATIONALE

Excessive fear and anxiety, coupled with corticolimbic dysfunction, are core features of stress- and trauma-related psychopathology, such as posttraumatic stress disorder (PTSD). Interestingly, low doses of ∆9-tetrahydrocannabinol (THC) can produce anxiolytic effects, reduce threat-related amygdala activation, and enhance functional coupling between the amygdala and medial prefrontal cortex and adjacent rostral cingulate cortex (mPFC/rACC) during threat processing in healthy adults. Together, these findings suggest the cannabinoid system as a potential pharmacological target in the treatment of excess fear and anxiety. However, the effects of THC on corticolimbic functioning in response to threat have not be investigated in adults with trauma-related psychopathology.

OBJECTIVE

To address this gap, the present study tests the effects of an acute low dose of THC on corticolimbic responses to threat in three groups of adults: (1) non-trauma-exposed healthy controls (HC; n = 25), (2) trauma-exposed adults without PTSD (TEC; n = 27), and (3) trauma-exposed adults with PTSD (n = 19).

METHODS

Using a randomized, double-blind, placebo-controlled, between-subjects design, 71 participants were randomly assigned to receive either THC or placebo (PBO) and subsequently completed a well-established threat processing paradigm during functional magnetic resonance imaging.

RESULTS

In adults with PTSD, THC lowered threat-related amygdala reactivity, increased mPFC activation during threat, and increased mPFC-amygdala functional coupling.

CONCLUSIONS

These preliminary data suggest that THC modulates threat-related processing in trauma-exposed individuals with PTSD, which may prove advantageous as a pharmacological approach to treating stress- and trauma-related psychopathology.

Anticipatory Threat Responding: Associations With Anxiety, Development, and Brain Structure

BACKGROUND

While translational theories link neurodevelopmental changes in threat learning to pathological anxiety, findings from studies in patients inconsistently support these theories. This inconsistency may reflect difficulties in studying large patient samples with wide age ranges using consistent methods. A dearth of imaging data in patients further limits translational advances. We address these gaps through a psychophysiology and structural brain imaging study in a large sample of patients across the lifespan.

METHODS

A total of 351 participants (8-50 years of age; 209 female subjects; 195 healthy participants and 156 medication-free, treatment-seeking patients with anxiety) completed a differential threat conditioning and extinction paradigm that has been validated in pediatric and adult populations. Skin conductance response indexed psychophysiological response to conditioned (CS+, CS-) and unconditioned threat stimuli. Structural magnetic resonance imaging data were available for 250 participants. Analyses tested anxiety and age associations with psychophysiological response in addition to associations between psychophysiology and brain structure.

RESULTS

Regardless of age, patients and healthy comparison subjects demonstrated comparable differential threat conditioning and extinction. The magnitude of skin conductance response to both conditioned stimulus types differentiated patients from comparison subjects and covaried with dorsal prefrontal cortical thickness; structure-response associations were moderated by anxiety and age in several regions. Unconditioned responding was unrelated to anxiety and brain structure.

CONCLUSIONS

Rather than impaired threat learning, pathological anxiety involves heightened skin conductance response to potential but not immediately present threats; this anxiety-related potentiation of anticipatory responding also relates to variation in brain structure. These findings inform theoretical considerations by highlighting anticipatory response to potential threat in anxiety.

Lateral orbitofrontal cortex partitions mechanisms for fear regulation and alcohol consumption

Anxiety disorders and alcohol use disorder are highly comorbid, yet identifying neural dysfunction driving comorbidity has been challenging. Lateral orbitofrontal cortex (lOFC) dysfunction has been independently observed in each disorder. Here we tested the hypothesis that the lOFC is essential to partition mechanisms for fear regulation and alcohol consumption. Specifically, the capacity to regulate fear and the propensity to consume alcohol are unrelated when lOFC is intact, but become linked through lOFC dysfunction. Male Long Evans rats received bilateral, neurotoxic lOFC lesions or sham surgery. Fear regulation was determined by establishing discrimination to danger, uncertainty, and safety cues then shifting the shock probability of the uncertainty cue. Alcohol consumption was assessed through voluntary, intermittent access to 20% ethanol. The neurotoxic lesion approach ensured lOFC dysfunction spanned testing in fear regulation and alcohol consumption. LOFC-lesioned rats demonstrated maladaptive fear generalization during probability shifts, inverting normal prediction error assignment, and subsequently consumed more alcohol. Most novel, fear regulation and alcohol consumption were inextricably linked only in lOFC-lesioned rats: extreme fear regulation predicted excessive alcohol consumption. The results reveal the lOFC is essential to partition mechanisms for fear regulation and alcohol consumption and uncover a plausible source of neural dysfunction contributing to comorbid anxiety disorders and alcohol use disorder.

Neural correlates of subjective CS/UCS association in appetitive conditioning

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

Altered reward learning and hippocampal connectivity following psychosocial stress

Acute stress has a profound influence on learning, as has been demonstrated in verbal learning or fear conditioning. However, its effect on appetitive conditioning is still unclear. Fear conditioning research suggests the possibility of overgeneralization of conditioning to the CS- under acute stress due to its effect on prefrontal and hippocampal processing. In this study, participants (N = 56 males) were subjected to the Trier Social Stress Test or a placebo version. After that, all participants underwent an appetitive conditioning paradigm in the fMRI, in which one neutral cue (CS+) was repeatedly paired with reward, while another (CS-) was not. Importantly, the stress-group revealed overgeneralization of conditioning to the CS- on the behavioral level. On the neural level, stressed participants showed increased connectivity between the hippocampus and amygdala, vACC, and OFC, which maintain specificity of conditioning and also showed reduced differential activation. The results indicate overgeneralization of appetitive conditioning promoted by maladaptive balancing of pattern separation and pattern completion in the hippocampus under acute stress and are discussed with respect to clinical implications.

Don't fear 'fear conditioning': Methodological considerations for the design and analysis of studies on human fear acquisition, extinction, and return of fear

The so-called 'replicability crisis' has sparked methodological discussions in many areas of science in general, and in psychology in particular. This has led to recent endeavours to promote the transparency, rigour, and ultimately, replicability of research. Originating from this zeitgeist, the challenge to discuss critical issues on terminology, design, methods, and analysis considerations in fear conditioning research is taken up by this work, which involved representatives from fourteen of the major human fear conditioning laboratories in Europe. This compendium is intended to provide a basis for the development of a common procedural and terminology framework for the field of human fear conditioning. Whenever possible, we give general recommendations. When this is not feasible, we provide evidence-based guidance for methodological decisions on study design, outcome measures, and analyses. Importantly, this work is also intended to raise awareness and initiate discussions on crucial questions with respect to data collection, processing, statistical analyses, the impact of subtle procedural changes, and data reporting specifically tailored to the research on fear conditioning.

Multimodal Imaging Evidence for a Frontoparietal Modulation of Visual Cortex during the Selective Processing of Conditioned Threat

Emotionally salient cues are detected more readily, remembered better, and evoke greater visual cortical responses compared with neutral stimuli. The current study used concurrent EEG-fMRI recordings to identify large-scale network interactions involved in the amplification of visual cortical activity when viewing aversively conditioned cues. To generate a continuous neural signal from pericalcarine visual cortex, we presented rhythmic (10/sec) phase-reversing gratings, the orientation of which predicted the presence (CS+) or absence (CS-) of a cutaneous electric shock (i.e., the unconditioned stimulus). The resulting single trial steady-state visual evoked potential (ssVEP) amplitude was regressed against the whole-brain BOLD signal, resulting in a measure of ssVEP-BOLD coupling. Across all trial types, ssVEP-BOLD coupling was observed in both primary and extended visual cortical regions, the rolandic operculum, as well as the thalamus and bilateral hippocampus. For CS+ relative to CS- trials during the conditioning phase, BOLD-alone analyses showed CS+ enhancement at the occipital pole, superior temporal sulci, and the anterior insula bilaterally, whereas ssVEP-BOLD coupling was greater in the pericalcarine cortex, inferior parietal cortex, and middle frontal gyrus. Dynamic causal modeling analyses supported connectivity models in which heightened activity in pericalcarine cortex for threat (CS+) arises from cortico-cortical top-down modulation, specifically from the middle frontal gyrus. No evidence was observed for selective pericalcarine modulation by deep cortical structures such as the amygdala or anterior insula, suggesting that the heightened engagement of pericalcarine cortex for threat stimuli is mediated by cortical structures that constitute key nodes of canonical attention networks.

Emotional Experience and Awareness of Self: Functional MRI Studies of Depersonalization Disorder

This paper presents functional MRI work on emotional processing in depersonalization disorder (DPD). This relatively neglected disorder is hallmarked by a disturbing change in the quality of first-person experience, almost invariably encompassing a diminished sense of self and an alteration in emotional experience such that the sufferer feels less emotionally reactive, with emotions experienced as decreased or “damped down,” so that emotional life seems to lack spontaneity and subjective validity. Here we explored responses to emotive visual stimuli to examine the functional neuroanatomy of emotional processing in DPD before and after pharmacological treatment. We also employed concurrent skin conductance measurement as an index of autonomic arousal. In common with previous studies we demonstrated that in DPD, there is attenuated psychophysiological response to emotional material, reflected in altered patterns of (i) regional brain response, (ii) autonomic responses. By scanning participants before and after treatment we were able to build on previous findings by examining the changes in functional MRI response in patients whose symptoms had improved at time 2. The attenuation of emotional experience was associated with reduced activity of the insula, whereas clinical improvement in DPD symptoms was associated with increased insula activity. The insula is known to be implicated in interoceptive awareness and the generation of feeling states. In addition an area of right ventrolateral prefrontal cortex emerged as particularly implicated in what may be “top-down” inhibition of emotional responses. The relevance of these findings to the wider study of emotion, self-related processes, and interoception is discussed.

Neural signatures of human fear conditioning: an updated and extended meta-analysis of fMRI studies

Classical Pavlovian fear conditioning remains the most widely employed experimental model of fear and anxiety, and continues to inform contemporary pathophysiological accounts of clinical anxiety disorders. Despite its widespread application in human and animal studies, the neurobiological basis of fear conditioning remains only partially understood. Here we provide a comprehensive meta-analysis of human fear-conditioning studies carried out with functional magnetic resonance imaging (fMRI), yielding a pooled sample of 677 participants from 27 independent studies. As a distinguishing feature of this meta-analysis, original statistical brain maps were obtained from the authors of 13 of these studies. Our primary analyses demonstrate that human fear conditioning is associated with a consistent and robust pattern of neural activation across a hypothesized genuine network of brain regions resembling existing anatomical descriptions of the 'central autonomic-interoceptive network'. This finding is discussed with a particular emphasis on the neural substrates of conscious fear processing. Our associated meta-analysis of functional deactivations-a scarcely addressed dynamic in fMRI fear-conditioning studies-also suggests the existence of a coordinated brain response potentially underlying the 'safety signal' (that is, non-threat) processing. We attempt to provide an integrated summary on these findings with the view that they may inform ongoing studies of fear-conditioning processes both in healthy and clinical populations, as investigated with neuroimaging and other experimental approaches.

Individual Differences in Anticipatory Somatosensory Cortex Activity for Shock is Positively Related with Trait Anxiety and Multisensory Integration

Anxiety is associated with an exaggerated expectancy of harm, including overestimation of how likely a conditioned stimulus (CS+) predicts a harmful unconditioned stimulus (US). In the current study we tested whether anxiety-associated expectancy of harm increases primary sensory cortex (S1) activity on non-reinforced (i.e., no shock) CS+ trials. Twenty healthy volunteers completed a differential-tone trace conditioning task while undergoing fMRI, with shock delivered to the left hand. We found a positive correlation between trait anxiety and activity in right, but not left, S1 during CS+ versus CS− conditions. Right S1 activity also correlated with individual differences in both primary auditory cortices (A1) and amygdala activity. Lastly, a seed-based functional connectivity analysis demonstrated that trial-wise S1 activity was positively correlated with regions of dorsolateral prefrontal cortex (dlPFC), suggesting that higher-order cognitive processes contribute to the anticipatory sensory reactivity. Our findings indicate that individual differences in trait anxiety relate to anticipatory reactivity for the US during associative learning. This anticipatory reactivity is also integrated along with emotion-related sensory signals into a brain network implicated in fear-conditioned responding.

A Stress-Induced Shift From Trace to Delay Conditioning Depends on the Mineralocorticoid Receptor

BACKGROUND

Fear learning in stressful situations is highly adaptive for survival by steering behavior in subsequent situations, but fear learning can become disproportionate in vulnerable individuals. Despite the potential clinical significance, the mechanism by which stress modulates fear learning is poorly understood. Memory theories state that stress can cause a shift away from more controlled processing depending on the hippocampus toward more reflexive processing supported by the amygdala and striatum. This shift may be mediated by activation of the mineralocorticoid receptor (MR) for cortisol. We investigated how stress shifts processes underlying cognitively demanding learning versus less demanding fear learning using a combined trace and delay fear conditioning paradigm.

METHODS

In a pharmacological functional magnetic resonance imaging study, we tested 101 healthy men probing the effects of stress (socially evaluated cold pressor vs. control procedure) and MR-availability (400 mg spironolactone vs. placebo) in a randomized, placebo-controlled, full-factorial, between-subjects design.

RESULTS

Effective stress induction and successful conditioning were confirmed by subjective, physiologic, and somatic data. In line with a stress-induced shift, stress enhanced later recall of delay compared with trace conditioning in the MR-available groups as indexed by skin conductance responses. During learning, this was accompanied by a stress-induced reduction of learning-related hippocampal activity for trace conditioning. The stress-induced shift in fear and neural processing was absent in the MR-blocked groups.

CONCLUSIONS

Our results are in line with a stress-induced shift in fear learning, mediated by the MR, resulting in a dominance of cognitively less demanding amygdala-based learning, which might be particularly prominent in individuals with high MR sensitivity.

Disruption of Memory Reconsolidation Erases a Fear Memory Trace in the Human Amygdala: An 18-Month Follow-Up

Fear memories can be attenuated by reactivation followed by disrupted reconsolidation. Using functional magnetic resonance imaging we recently showed that reactivation and reconsolidation of a conditioned fear memory trace in the basolateral amygdala predicts subsequent fear expression over two days, while reactivation followed by disrupted reconsolidation abolishes the memory trace and suppresses fear. In this follow-up study we demonstrate that the behavioral effect persists over 18 months reflected in superior reacquisition after undisrupted, as compared to disrupted reconsolidation, and that neural activity in the basolateral amygdala representing the initial fear memory predicts return of fear. We conclude that disrupting reconsolidation have long lasting behavioral effects and may permanently erase the fear component of an amygdala-dependent memory.

Impact of COMT Val158Met-polymorphism on appetitive conditioning and amygdala/prefrontal effective connectivity

Appetitive conditioning is an important mechanism for the development, maintenance, and treatment of psychiatric disorders like substance abuse. Therefore, it is important to identify genetic variations, which impact appetitive conditioning. It has been suggested that the Val(158) Met-polymorphism in the Catechol-O-Methyl-Transferase (COMT) is associated with the alteration of neural processes of appetitive conditioning due to the central role of the dopaminergic system in reward processing. However, no study has so far investigated the relationship between variations in the COMT Val(158) Met-polymorphism and appetitive conditioning. In this fMRI study, an appetitive conditioning paradigm was applied, in which one neutral stimulus (CS+) predicted appetitive stimuli (UCS) while a second neutral stimulus (CS-) was never paired with the UCS. As a main result, we observed a significant association between the COMT Val(158) Met-genotype and appetitive conditioning: skin conductance responses (SCRs) revealed a significant difference between CS+ and CS- in Val/Val-allele carriers but not in the other genotype groups. Val/Val-allele carriers showed increased hemodynamic responses in the amygdala compared with the Met/Met-allele group in the contrast CS+ > CS-. In addition, psychophysiological-interaction analysis revealed increased effective amygdala/ventromedial prefrontal cortex connectivity in Met/Met-allele carriers. The increased amygdala activity points to facilitated appetitive conditioning in Val/Val-allele carriers while the amygdala/prefrontal connectivity results could be regarded as a marker for altered emotion regulation during conditioning, which potentially impacts appetitive learning sensitivity. The SCRs finding indicates a stronger conditioned response in the Val/Val-allele group and dovetails with the neural differences between the groups. These findings contribute to the current research on COMT in emotional processing.

Equal pain-Unequal fear response: enhanced susceptibility of tooth pain to fear conditioning

Experimental fear conditioning in humans is widely used as a model to investigate the neural basis of fear learning and to unravel the pathogenesis of anxiety disorders. It has been observed that fear conditioning depends on stimulus salience and subject vulnerability to fear. It is further known that the prevalence of dental-related fear and phobia is exceedingly high in the population. Dental phobia is unique as no other body part is associated with a specific phobia. Therefore, we hypothesized that painful dental stimuli exhibit an enhanced susceptibility to fear conditioning when comparing to equal perceived stimuli applied to other body sites. Differential susceptibility to pain-related fear was investigated by analyzing responses to an unconditioned stimulus (UCS) applied to the right maxillary canine (UCS-c) vs. the right tibia (UCS-t). For fear conditioning, UCS-c and USC-t consisted of painful electric stimuli, carefully matched at both application sites for equal intensity and quality perception. UCSs were paired to simple geometrical forms which served as conditioned stimuli (CS+). Unpaired CS+ were presented for eliciting and analyzing conditioned fear responses. Outcome parameter were (1) skin conductance changes and (2) time-dependent brain activity (BOLD responses) in fear-related brain regions such as the amygdala, anterior cingulate cortex, insula, thalamus, orbitofrontal cortex, and medial prefrontal cortex. A preferential susceptibility of dental pain to fear conditioning was observed, reflected by heightened skin conductance responses and enhanced time-dependent brain activity (BOLD responses) in the fear network. For the first time, this study demonstrates fear-related neurobiological mechanisms that point toward a superior conditionability of tooth pain. Beside traumatic dental experiences our results offer novel evidence that might explain the high prevalence of dental-related fears in the population.

Are you gonna leave me? Separation anxiety is associated with increased amygdala responsiveness and volume

The core feature of separation anxiety is excessive distress when faced with actual or perceived separation from people to whom the individual has a strong emotional attachment. So far little is known about the neurobiological underpinnings of separation anxiety. Therefore, we investigated functional (amygdala responsiveness and functional connectivity during threat-related emotion processing) and structural (grey matter volume) imaging markers associated with separation anxiety as measured with the Relationship Scale Questionnaire in a large sample of healthy adults from the Münster Neuroimaging Cohort (N = 320). We used a robust emotional face-matching task and acquired high-resolution structural images for morphometric analyses using voxel-based morphometry. The main results were positive associations of separation anxiety scores with amygdala reactivity to emotional faces as well as increased amygdala grey matter volumes. A functional connectivity analysis revealed positive associations between separation anxiety and functional coupling of the amygdala with areas involved in visual processes and attention, including several occipital and somatosensory areas. Taken together, the results suggest a higher emotional involvement in subjects with separation anxiety while watching negative facial expressions, and potentially secondary neuro-structural adaptive processes. These results could help to understand and treat (adult) separation anxiety.

Correlation Between Activation of the Prelimbic Cortex, Basolateral Amygdala, and Agranular Insular Cortex During Taste Memory Formation

Conditioned taste aversion (CTA) is a well-established learning paradigm, whereby animals associate tastes with subsequent visceral illness. The prelimbic cortex (PL) has been shown to be involved in the association of events separated by time. However, the nature of PL activity and its functional network in the whole brain during CTA learning remain unknown. Here, using awake functional magnetic resonance imaging and fiber tracking, we analyzed functional brain connectivity during the association of tastes and visceral illness. The blood oxygen level-dependent (BOLD) signal significantly increased in the PL after tastant and lithium chloride (LiCl) infusions. The BOLD signal in the PL significantly correlated with those in the amygdala and agranular insular cortex (IC), which we found were also structurally connected to the PL by fiber tracking. To precisely examine these data, we then performed double immunofluorescence with a neuronal activity marker (c-Fos) and an inhibitory neuron marker (GAD67) combined with a fluorescent retrograde tracer in the PL. During CTA learning, we found an increase in the activity of excitatory neurons in the basolateral amygdala (BLA) or agranular IC that project to the PL. Taken together, these findings clearly identify a role of synchronized PL, agranular IC, and BLA activity in CTA learning.

Potentiation of the early visual response to learned danger signals in adults and adolescents

The reinforcing effects of aversive outcomes on avoidance behaviour are well established. However, their influence on perceptual processes is less well explored, especially during the transition from adolescence to adulthood. Using electroencephalography, we examined whether learning to actively or passively avoid harm can modulate early visual responses in adolescents and adults. The task included two avoidance conditions, active and passive, where two different warning stimuli predicted the imminent, but avoidable, presentation of an aversive tone. To avoid the aversive outcome, participants had to learn to emit an action (active avoidance) for one of the warning stimuli and omit an action for the other (passive avoidance). Both adults and adolescents performed the task with a high degree of accuracy. For both adolescents and adults, increased N170 event-related potential amplitudes were found for both the active and the passive warning stimuli compared with control conditions. Moreover, the potentiation of the N170 to the warning stimuli was stable and long lasting. Developmental differences were also observed; adolescents showed greater potentiation of the N170 component to danger signals. These findings demonstrate, for the first time, that learned danger signals in an instrumental avoidance task can influence early visual sensory processes in both adults and adolescents.

Role of the hippocampus and orbitofrontal cortex during the disambiguation of social cues in working memory

Human social interactions are complex behaviors requiring the concerted effort of multiple neural systems to track and monitor the individuals around us. Cognitively, adjusting our behavior on the basis of changing social cues such as facial expressions relies on working memory and the ability to disambiguate, or separate, the representations of overlapping stimuli resulting from viewing the same individual with different facial expressions. We conducted an fMRI experiment examining the brain regions contributing to the encoding, maintenance, and retrieval of overlapping identity information during working memory using a delayed match-to-sample task. In the overlapping condition, two faces from the same individual with different facial expressions were presented at sample. In the nonoverlapping condition, the two sample faces were from two different individuals with different expressions. fMRI activity was assessed by contrasting the overlapping and nonoverlapping conditions at sample, delay, and test. The lateral orbitofrontal cortex showed increased fMRI signal in the overlapping condition in all three phases of the delayed match-to-sample task and increased functional connectivity with the hippocampus when encoding overlapping stimuli. The hippocampus showed increased fMRI signal at test. These data suggest that lateral orbitofrontal cortex helps encode and maintain representations of overlapping stimuli in working memory, whereas the orbitofrontal cortex and hippocampus contribute to the successful retrieval of overlapping stimuli. We suggest that the lateral orbitofrontal cortex and hippocampus play a role in encoding, maintaining, and retrieving social cues, especially when multiple interactions with an individual need to be disambiguated in a rapidly changing social context in order to make appropriate social responses.

The scent of salience--is there olfactory-trigeminal conditioning in humans?

Pavlovian fear conditioning has been thoroughly studied in the visual, auditory and somatosensory domain, but evidence is scarce with regard to the chemosensory modality. Under the assumption that Pavlovian conditioning relies on the supra-modal mechanism of salience attribution, the present study was set out to attest the existence of chemosensory aversive conditioning in humans as a specific instance of salience attribution. fMRI was performed in 29 healthy subjects during a differential aversive conditioning paradigm. Two odors (rose, vanillin) served as conditioned stimuli (CS), one of which (CS+) was intermittently coupled with intranasally administered CO2. On the neural level, a robust differential response to the CS+ emerged in frontal, temporal, occipito-parietal and subcortical brain regions, including the amygdala. These changes were paralleled by the development of a CS+-specific connectivity profile of the anterior midcingulate cortex (aMCC), which is a key structure for processing salience information in order to guide adaptive response selection. Increased coupling could be found between key nodes of the salience network (anterior insula, neo-cerebellum) and sensorimotor areas, representing putative input and output structures of the aMCC for exerting adaptive motor control. In contrast, behavioral and skin conductance responses did not show significant effects of conditioning, which has been attributed to contingency unawareness. These findings imply substantial similarities of conditioning involving chemosensory and other sensory modalities, and suggest that salience attribution and adaptive control represent a general, modality-independent principle underlying Pavlovian conditioning.

Fear conditioning in an abdominal pain model: neural responses during associative learning and extinction in healthy subjects

Fear conditioning is relevant for elucidating the pathophysiology of anxiety, but may also be useful in the context of chronic pain syndromes which often overlap with anxiety. Thus far, no fear conditioning studies have employed aversive visceral stimuli from the lower gastrointestinal tract. Therefore, we implemented a fear conditioning paradigm to analyze the conditioned response to rectal pain stimuli using fMRI during associative learning, extinction and reinstatement.

In N = 21 healthy humans, visual conditioned stimuli (CS⁺) were paired with painful rectal distensions as unconditioned stimuli (US), while different visual stimuli (CS⁻) were presented without US. During extinction, all CSs were presented without US, whereas during reinstatement, a single, unpaired US was presented. In region-of-interest analyses, conditioned anticipatory neural activation was assessed along with perceived CS-US contingency and CS unpleasantness.

Fear conditioning resulted in significant contingency awareness and valence change, i.e., learned unpleasantness of a previously neutral stimulus. This was paralleled by anticipatory activation of the anterior cingulate cortex, the somatosensory cortex and precuneus (all during early acquisition) and the amygdala (late acquisition) in response to the CS⁺. During extinction, anticipatory activation of the dorsolateral prefrontal cortex to the CS⁻ was observed. In the reinstatement phase, a tendency for parahippocampal activation was found.

Fear conditioning with rectal pain stimuli is feasible and leads to learned unpleasantness of previously neutral stimuli. Within the brain, conditioned anticipatory activations are seen in core areas of the central fear network including the amygdala and the anterior cingulate cortex. During extinction, conditioned responses quickly disappear, and learning of new predictive cue properties is paralleled by prefrontal activation. A tendency for parahippocampal activation during reinstatement could indicate a reactivation of the old memory trace. Together, these findings contribute to our understanding of aversive visceral learning and memory processes relevant to the pathophysiology of chronic abdominal pain.

Hemodynamic responses in amygdala and hippocampus distinguish between aversive and neutral cues during Pavlovian fear conditioning in behaving rats

Lesion and electrophysiological studies in rodents have identified the amygdala and hippocampus (HPC) as key structures for Pavlovian fear conditioning, but human functional neuroimaging studies have not consistently found activation of these structures. This could be because hemodynamic responses cannot detect the sparse neuronal activity proposed to underlie conditioned fear. Alternatively, differences in experimental design or fear levels could account for the discrepant findings between rodents and humans. To help distinguish between these alternatives, we used tissue oxygen amperometry to record hemodynamic responses from the basolateral amygdala (BLA), dorsal HPC (dHPC) and ventral HPC (vHPC) in freely-moving rats during the acquisition and extinction of conditioned fear. To enable specific comparison with human studies we used a discriminative paradigm, with one auditory cue [conditioned stimulus (CS)+] that was always followed by footshock, and another auditory cue (CS-) that was never followed by footshock. BLA tissue oxygen signals were significantly higher during CS+ than CS- trials during training and early extinction. In contrast, they were lower during CS+ than CS- trials by the end of extinction. dHPC and vHPC tissue oxygen signals were significantly lower during CS+ than CS- trials throughout extinction. Thus, hemodynamic signals in the amygdala and HPC can detect the different patterns of neuronal activity evoked by threatening vs. neutral stimuli during fear conditioning. Discrepant neuroimaging findings may be due to differences in experimental design and/or fear levels evoked in participants. Our methodology offers a way to improve translation between rodent models and human neuroimaging.

Common brain activations for painful and non-painful aversive stimuli

BACKGROUND

Identification of potentially harmful stimuli is necessary for the well-being and self-preservation of all organisms. However, the neural substrates involved in the processing of aversive stimuli are not well understood. For instance, painful and non-painful aversive stimuli are largely thought to activate different neural networks. However, it is presently unclear whether there is a common aversion-related network of brain regions responsible for the basic processing of aversive stimuli. To help clarify this issue, this report used a cross-species translational approach in humans (i.e. meta-analysis) and rodents (i.e. systematic review of functional neuroanatomy).

RESULTS

Animal and human data combined to show a core aversion-related network, consisting of similar cortical (i.e. MCC, PCC, AI, DMPFC, RTG, SMA, VLOFC; see results section or abbreviation section for full names) and subcortical (i.e. Amyg, BNST, DS, Hab, Hipp/Parahipp, Hyp, NAc, NTS, PAG, PBN, raphe, septal nuclei, Thal, LC, midbrain) regions. In addition, a number of regions appeared to be more involved in pain-related (e.g. sensory cortex) or non-pain-related (e.g. amygdala) aversive processing.

CONCLUSIONS

This investigation suggests that aversive processing, at the most basic level, relies on similar neural substrates, and that differential responses may be due, in part, to the recruitment of additional structures as well as the spatio-temporal dynamic activity of the network. This network perspective may provide a clearer understanding of why components of this circuit appear dysfunctional in some psychiatric and pain-related disorders.

Neuronal correlates of extinction learning are modulated by sex hormones

In emotional learning tasks, sex differences, stress effects and an interaction of these two moderators have often been observed. The sex hormones estradiol (E2) and progesterone (P4) vary over the menstrual cycle. We tested groups with different sex hormone status: 39 men, 30 women in the luteal phase (LU, high E2+P4) and 29 women taking oral contraceptives (OC, low E2+P4). They received either 30 mg cortisol or placebo prior to instructed differential fear conditioning consisting of neutral conditioned stimuli (CS) and an electrical stimulation (unconditioned stimulus; UCS). One figure (CS+) was paired with the UCS, the other figure (CS-) never. During extinction, no electrical stimulation was administered. Regarding fear acquisition, results showed higher skin conductance and higher brain responses to the CS+ compared to the CS- in several structures that were not modulated by cortisol or sex hormones. However, OC women exhibited higher CS+/CS- differentiations than men and LU women in the amygdala, thalamus, anterior cingulate and ventromedial prefrontal cortex during extinction. The suppression of endogenous sex hormones by OC seems to alter neuronal correlates of extinction. The observation that extinction is influenced by the current sex hormone availability is relevant for future studies and might also be clinically important.

Identifying a network of brain regions involved in aversion-related processing: a cross-species translational investigation

The ability to detect and respond appropriately to aversive stimuli is essential for all organisms, from fruit flies to humans. This suggests the existence of a core neural network which mediates aversion-related processing. Human imaging studies on aversion have highlighted the involvement of various cortical regions, such as the prefrontal cortex, while animal studies have focused largely on subcortical regions like the periaqueductal gray and hypothalamus. However, whether and how these regions form a core neural network of aversion remains unclear. To help determine this, a translational cross-species investigation in humans (i.e., meta-analysis) and other animals (i.e., systematic review of functional neuroanatomy) was performed. Our results highlighted the recruitment of the anterior cingulate cortex, the anterior insula, and the amygdala as well as other subcortical (e.g., thalamus, midbrain) and cortical (e.g., orbitofrontal) regions in both animals and humans. Importantly, involvement of these regions remained independent of sensory modality. This study provides evidence for a core neural network mediating aversion in both animals and humans. This not only contributes to our understanding of the trans-species neural correlates of aversion but may also carry important implications for psychiatric disorders where abnormal aversive behavior can often be observed.

Emotion-associated tones attract enhanced attention at early auditory processing: magnetoencephalographic correlates

Emotionally significant objects and events in our environment attract attention based on their motivational relevance for survival. Such kind of emotional attention is thought to lead to affect-specific amplified processing that closely resembles effects of directed attention. Although there has been extensive research on prioritized processing of visual emotional stimuli, the spatio-temporal dynamics of motivated attention mechanisms in auditory processing are less clearly understood. We investigated modulatory effects of emotional attention at early auditory processing stages using time-sensitive whole-head magnetoencephalography. A novel associative learning procedure involving multiple conditioned stimuli (CSs) per affective category was introduced to specifically test whether affect-specific modulation can proceed in a rapid and highly differentiating fashion in humans. Auditory evoked fields (AEFs) were recorded in response to 42 different ultrashort, click-like sounds before and after affective conditioning with pleasant, unpleasant, or neutral auditory scenes. As hypothesized, emotional attention affected neural click tone processing at time intervals of the P20-50m (20-50 ms) and the N1m (100-130 ms), two early AEF components sensitive to directed selective attention (Woldorff et al., 1993). Distributed source localization revealed amplified processing of tones associated with aversive or pleasant compared with neutral auditory scenes at auditory sensory, frontal and parietal cortex regions. Behavioral tests did not indicate any awareness for the contingent CS-UCS (unconditioned stimulus) relationships in the participants, suggesting affective associative learning in absence of contingency awareness. Our findings imply early and highly differentiating affect-specific modulation of auditory stimulus processing supported by neural mechanisms and circuitry comparable with those reported for directed auditory attention.

A psychophysiological investigation of moral judgment after ventromedial prefrontal damage

Converging evidence suggests that emotion processing mediated by ventromedial prefrontal cortex (vmPFC) is necessary to prevent personal moral violations. In moral dilemmas, for example, patients with lesions in vmPFC are more willing than normal controls to approve harmful actions that maximize good consequences (e.g., utilitarian moral judgments). Yet, none of the existing studies has measured subjects' emotional responses while they considered moral dilemmas. Therefore, a direct link between emotion processing and moral judgment is still lacking. Here, vmPFC patients and control participants considered moral dilemmas while skin conductance response (SCR) was measured as a somatic index of affective state. Replicating previous evidence, vmPFC patients approved more personal moral violations than did controls. Critically, we found that, unlike control participants, vmPFC patients failed to generate SCRs before endorsing personal moral violations. In addition, such anticipatory SCRs correlated negatively with the frequency of utilitarian judgments in normal participants. These findings provide direct support to the hypothesis that the vmPFC promotes moral behavior by mediating the anticipation of the emotional consequences of personal moral violations.

Investigating the impact of sex and cortisol on implicit fear conditioning with fMRI

Fear conditioning is influenced by stress but opposing effects in males and females have often been reported. In a previous human functional magnetic resonance imaging (fMRI) study, we observed acute effects of the stress hormone cortisol on prefrontal structures. Men showed evidence for impaired fear conditioning after cortisol treatment, while the opposite pattern was found for women. In the current experiment, we tested whether similar sex-dependent effects would occur on the neural level if contingency awareness was prevented experimentally to investigate implicit learning processes. A differential fear conditioning experiment with transcutaneous electrical stimulation as unconditioned stimulus and geometric figures as conditioned stimuli (CS) was conducted. One figure was always paired (CS+), whereas the other (CS-) was never paired with the UCS. Thirty-nine (19 female) subjects participated in this fMRI study, receiving either placebo or 30 mg cortisol (hydrocortisone) before conditioning. Dependent variables were skin conductance responses (SCRs) and neural activity (BOLD signal). In line with prior findings in unaware participants, no differential learning could be observed for the SCRs. However, a sex x cortisol interaction was detected with a reduced mean response to the CS after cortisol treatment in men, while the opposite pattern was observed in women (enhanced mean SCR under cortisol). In the contrast CS+ minus CS-, neural activity showed a sex x cortisol interaction in the insula and further trends in the hippocampus and the thalamus. In these regions, cortisol reduced the CS+/CS- differentiation in men but enhanced it in women. In contrast to these sex specific effects, differential amygdala activation was found in the placebo group but not in the cortisol group, irrespective of sex. Further, differential neural activity in the amygdala and thalamus were positively correlated with the SCRs in the placebo group only. The present study in contingency unaware participants illustrates that cortisol has in some brain regions sex specific effects on neural correlates of emotional learning. These effects might translate into a different vulnerability of the two sexes for anxiety disorders.

Contingency learning in human fear conditioning involves the ventral striatum

The ability to detect and learn contingencies between fearful stimuli and their predictive cues is an important capacity to cope with the environment. Contingency awareness refers to the ability to verbalize the relationships between conditioned and unconditioned stimuli. Although there is a heated debate about the influence of contingency awareness on conditioned fear responses, neural correlates behind the formation process of contingency awareness have gained only little attention in human fear conditioning. Recent animal studies indicate that the ventral striatum (VS) could be involved in this process, but in human studies the VS is mostly associated with positive emotions. To examine this question, we reanalyzed four recently published classical fear conditioning studies (n = 117) with respect to the VS at three distinct levels of contingency awareness: subjects, who did not learn the contingencies (unaware), subjects, who learned the contingencies during the experiment (learned aware) and subjects, who were informed about the contingencies in advance (instructed aware). The results showed significantly increased activations in the left and right VS in learned aware compared to unaware subjects. Interestingly, this activation pattern was only found in learned but not in instructed aware subjects. We assume that the VS is not involved when contingency awareness does not develop during conditioning or when contingency awareness is unambiguously induced already prior to conditioning. VS involvement seems to be important for the transition from a contingency unaware to a contingency aware state. Implications for fear conditioning models as well as for the contingency awareness debate are discussed.

Neural activations of the acquisition of conditioned sexual arousal: effects of contingency awareness and sex

INTRODUCTION

Learning processes like classical conditioning are involved in mediating sexual behavior. Yet, the neural bases underlying these processes have not been investigated so far.

AIM

The aim of this study was to explore neural activations of classical conditioning of sexual arousal with respect to sex differences and contingency awareness.

METHODS

In the acquisition phase, a geometric figure (CS+) was presented for 8 seconds and was followed by highly sexual arousing pictures (UCS), whereas another figure (CS-) predicted neutral pictures. Ratings and contingency awareness were assessed after the entire conditioning procedure. Forty subjects (20 females) were classified into one of four groups according to their sex and the development of contingency awareness (aware females, aware males, unaware females, and unaware males).

MAIN OUTCOME MEASURES

Blood oxygen level dependent (BOLD) responses measured by functional magnetic resonance imaging (fMRI), skin conductance responses (SCRs), and subjective ratings.

RESULTS

fMRI analysis showed two effects (awareness and sex) when comparing CS+ with CS-: (i) aware compared to unaware subjects showed enhanced differentiation (e.g., ventral striatum, orbitofrontal cortex, occipital cortex); and (ii) men showed increased activity compared to women in the amygdala, thalamus, and brainstem. CS+ and CS- ratings differed in aware subjects only. However, no conditioned SCRs occurred in any group.

CONCLUSION

The increased activity in men is in line with theories postulating that men are generally more prone to conditioning of sexual arousal. Further, contingency awareness seems to be an important factor in appetitive learning processes, which facilitates conditioning processes.

Learning-related diminution of unconditioned SCR and fMRI signal responses

During Pavlovian conditioning the expression of a conditioned response is typically taken as evidence that an association between a conditioned stimulus (CS) and an unconditioned stimulus (UCS) has been formed. However, learning-related changes in the unconditioned response (UCR) produced by a predictable UCS can also develop. Learning-related reductions in UCR magnitude are often referred to as UCR diminution. In the present study, we examined UCR diminution in the functional magnetic resonance imaging (fMRI) signal by pairing supra- and sub-threshold CS presentations with a UCS. UCR diminution was observed within several brain regions associated with fear learning and memory including the insula, inferior parietal lobe, ventromedial prefrontal cortex (PFC), dorsomedial PFC, and dorsolateral PFC. CS perception appeared to mediate UCR diminution within the ventromedial PFC and posterior cingulate cortex. UCRs within these regions were larger when the UCS followed an unperceived compared to a perceived CS. UCS expectancies appeared to modulate UCRs within the dorsomedial PFC, dorsolateral PFC, insula, and inferior parietal lobe. Activity within these regions showed an inverse relationship with participants' UCS expectancies, such that as UCS expectancy increased UCR magnitude decreased. In addition, activity within the dorsomedial PFC, dorsolateral PFC, and insula showed a linear relationship with unconditioned skin conductance response (SCR) expression. These findings demonstrate UCR diminution within the fMRI signal, and suggest that UCS expectancies modulate prefrontal cortex responses to aversive stimuli. In turn, prefrontal cortex activity appears to modulate the expression of unconditioned SCRs.

Human fear conditioning and extinction in neuroimaging: a systematic review

Fear conditioning and extinction are basic forms of associative learning that have gained considerable clinical relevance in enhancing our understanding of anxiety disorders and facilitating their treatment. Modern neuroimaging techniques have significantly aided the identification of anatomical structures and networks involved in fear conditioning. On closer inspection, there is considerable variation in methodology and results between studies. This systematic review provides an overview of the current neuroimaging literature on fear conditioning and extinction on healthy subjects, taking into account methodological issues such as the conditioning paradigm.

A Pubmed search, as of December 2008, was performed and supplemented by manual searches of bibliographies of key articles. Two independent reviewers made the final study selection and data extraction. A total of 46 studies on cued fear conditioning and/or extinction on healthy volunteers using positron emission tomography or functional magnetic resonance imaging were reviewed. The influence of specific experimental factors, such as contingency and timing parameters, assessment of conditioned responses, and characteristics of conditioned and unconditioned stimuli, on cerebral activation patterns was examined. Results were summarized descriptively. A network consisting of fear-related brain areas, such as amygdala, insula, and anterior cingulate cortex, is activated independently of design parameters. However, some neuroimaging studies do not report these findings in the presence of methodological heterogeneities. Furthermore, other brain areas are differentially activated, depending on specific design parameters. These include stronger hippocampal activation in trace conditioning and tactile stimulation. Furthermore, tactile unconditioned stimuli enhance activation of pain related, motor, and somatosensory areas.

Differences concerning experimental factors may partly explain the variance between neuroimaging investigations on human fear conditioning and extinction and should, therefore, be taken into serious consideration in the planning and the interpretation of research projects.

Neural, electrodermal and behavioral response patterns in contingency aware and unaware subjects during a picture-picture conditioning paradigm

One way of investigating affective learning is the use of aversive pictures as unconditioned stimuli (UCS) in conditioning paradigms. In the last decades, there has been a heated debate on the influence of contingency awareness on conditioned responses (CRs). Only a few studies found CRs in contingency unaware subjects whereas other studies only reported conditioned reactions in contingency aware participants. However, as a shortcoming, most studies employing picture-picture paradigms only investigated one response level (e.g. changes in subjective ratings). Further, changes in brain activity have so far been neglected in this field of research. The aim of the present study was to investigate different response levels with respect to contingency awareness: brain activity measured by functional magnetic resonance imaging (fMRI), skin conductance responses (SCRs) and valence ratings. A neutral geometric shape (conditioned stimulus, CS+) was followed by aversive pictures, whereas another shape (CS-) preceded neutral pictures. Unaware participants showed CRs in brain activity (e.g. the insula). Generally more activity was observed in the fear network (e.g. the amygdala, the lateral orbitofrontal cortex) in aware participants and in the nucleus accumbens (NAcc). Investigation of SCRs and valence ratings revealed that only aware participants showed conditioned reactions. Our results point toward dissociations between response levels (e.g. brain activity) not affected by contingency awareness and more cognitive response levels (e.g. subjective ratings and SCRs) which are affected by contingency awareness. As a unique finding in human aversive conditioning, we discuss the role of the nucleus accumbens as well as practical implications for affective learning models.

Learning affective values for faces is expressed in amygdala and fusiform gyrus

To monitor the environment for social threat humans must build affective evaluations of others. These evaluations are malleable and to a high degree shaped by responses engendered by specific social encounters. The precise neuronal mechanism by which these evaluations are constructed is poorly understood. We tested a hypothesis that conjoint activity in amygdala and fusiform gyrus would correlate with acquisition of social stimulus value. We tested this using a reinforcement learning algorithm, Q-learning, that assigned values to faces as a function of a history of pairing, or not pairing, with aversive shocks. Behaviourally, we observed a correlation between conditioning induced changes in skin conductance response (SCR) and subjective ratings for likeability of faces. Activity in both amygdala and fusiform gyrus (FG) correlated with the output of the reinforcement learning algorithm parameterized by these ratings. In amygdala, this effect was greater for averted than direct gaze faces. Furthermore, learning-related activity change in these regions correlated with SCR and subjective ratings. We conclude that amygdala and fusiform encode affective value in a manner that closely approximates a standard computational solution to learning.

Neural correlates of unconditioned response diminution during Pavlovian conditioning

Pavlovian conditioning research has shown that unconditioned responses (UCR) to aversive unconditioned stimuli (UCS) are reduced when a UCS is predictable. This effect is known as UCR diminution. In the present study, we examined UCR diminution in the functional magnetic resonance imaging (fMRI) signal by varying the rate at which a neutral conditioned stimulus (CS) was paired with an aversive UCS. UCR diminution was observed within several brain regions associated with fear learning, including the amygdala, anterior cingulate, auditory cortex, and dorsolateral prefrontal cortex when a CS continuously relative to intermittently predicted the UCS. In addition, an inverse relationship between UCS expectancy and UCR magnitude was observed within the amygdala, anterior cingulate, and dorsolateral prefrontal cortex, such that as UCS expectancy increased the UCR decreased. These findings demonstrate UCR diminution within the fMRI signal, and suggest that UCS expectancies modulate UCR magnitude.

Recall of fear extinction in humans activates the ventromedial prefrontal cortex and hippocampus in concert

BACKGROUND

Extinction of conditioned fear is thought to form a new safety memory that is expressed in the context in which the extinction learning took place. Rodent studies implicate the ventromedial prefrontal cortex (vmPFC) and hippocampus in extinction recall and its modulation by context, respectively. The aim of the present study is to investigate the mediating anatomy of extinction recall in healthy humans.

METHODS

We used event-related functional magnetic resonance imaging (fMRI) and a 2-day fear conditioning and extinction protocol with skin conductance response as the index of conditioned responses.

RESULTS

During extinction recall, we found significant activations in vmPFC and hippocampus in response to the extinguished versus an unextinguished stimulus. Activation in these brain regions was positively correlated with the magnitude of extinction memory. Functional connectivity analysis revealed significant positive correlation between vmPFC and hippocampal activation during extinction recall.

CONCLUSIONS

These results support the involvement of the human hippocampus as well as vmPFC in the recall of extinction memory. Furthermore, this provides a paradigm for future investigations of fronto-temporal function during extinction recall in psychiatric disorders such as posttraumatic stress disorder.