Parallel neural responses in amygdala subregions and sensory cortex during implicit fear conditioning

We used event-related fMRI to measure neural activity in volunteer subjects during acquisition of an implicit association between a visual conditioned stimulus (CS+) (angry face) and an auditory unconditioned stimulus (UCS) (aversive, loud noise). Three distinct functional regions were identified within left amygdala: a UCS (noise)-related lateral region, a CS+-related ventral region, and a dorsal region where CS+-related responses changed progressively across the learning session. Differential neural responses to the visual CS+ were also evoked in extrastriate and auditory cortices. Our results indicate that learning an association between biologically salient stimuli of different sensory modalities involves parallel changes of neural activity in segregated amygdala subregions and unimodal sensory cortices.

Brain activity during biofeedback relaxation: a functional neuroimaging investigation

The mechanisms by which cognitive processes influence states of bodily arousal are important for understanding the pathogenesis and maintenance of stress-related morbidity. We used PET to investigate cerebral activity relating to the cognitively driven modulation of sympathetic activity. Subjects were trained to perform a biofeedback relaxation exercise that reflected electrodermal activity and were subsequently scanned performing repetitions of four tasks: biofeedback relaxation, relaxation without biofeedback and two corresponding control conditions in which the subjects were instructed not to relax. Relaxation was associated with significant increases in left anterior cingulate and globus pallidus activity, whereas no significant increases in activity were associated with biofeedback compared with random feedback. The interaction between biofeedback and relaxation, highlighting activity unique to biofeedback relaxation, was associated with enhanced anterior cingulate and cerebellar vermal activity. These data implicate the anterior cingulate cortex in the intentional modulation of bodily arousal and suggest a functional neuroanatomy of how cognitive states are integrated with bodily responses. The findings have potential implications for a mechanistic account of how therapeutic interventions, such as relaxation training in stress-related disorders, mediate their effects.

Neuroanatomical basis for first- and second-order representations of bodily states

Changes in bodily states, particularly those mediated by the autonomic nervous system, are crucial to ongoing emotional experience. A theoretical model proposes a first-order autoregulatory representation of bodily state at the level of dorsal pons, and a second-order experience-dependent re-mapping of changes in bodily state within structures such as cingulate and medial parietal cortices. We tested these anatomical predictions using positron emission tomography and a human neurological model (pure autonomic failure), in which peripheral autonomic denervation prevents the emergence of autonomic responses. Compared to controls, we observed task-independent differences in activity of dorsal pons and context-induced differences in cingulate and medial parietal activity in PAF patients. An absence of afferent feedback concerning autonomically generated bodily states was associated with subtle impairments of emotional responses in PAF patients. Our findings provide empirical support for a theory proposing a hierarchical representation of bodily states.

Neural activity in the human brain relating to uncertainty and arousal during anticipation

We used functional magnetic resonance neuroimaging to measure brain activity during delay between reward-related decisions and their outcomes, and the modulation of this delay activity by uncertainty and arousal. Feedback, indicating financial gain or loss, was given following a fixed delay. Anticipatory arousal was indexed by galvanic skin conductance. Delay-period activity was associated with bilateral activation in orbital and medial prefrontal, temporal, and right parietal cortices. During delay, activity in anterior cingulate and orbitofrontal cortices was modulated by outcome uncertainty, whereas anterior cingulate, dorsolateral prefrontal, and parietal cortices activity was modulated by degree of anticipatory arousal. A distinct region of anterior cingulate was commonly activated by both uncertainty and arousal. Our findings highlight distinct contributions of cognitive uncertainty and autonomic arousal to anticipatory neural activity in prefrontal cortex.

Switching between the forest and the trees: brain systems involved in local/global changed-level judgments

Visual targets can be coded, in relative terms, at either the local or the global level of stimuli. Previous studies have indicated that targets are identified more slowly when they appear at a new hierarchical level, compared to when they reappear at the same level as in the previous trial. In the present study, we used measures of reaction time and event-related fMRI to investigate factors affecting this switch cost. In particular, we examined the effects of the number of repeated-level trials preceding a switch and whether the cue to switch was either externally or internally mediated. At the behavioral level we found that (1) the time taken to identify a target on a changed-level trial is longer following four repeated-level trials compared to two repeated-level trials, but that runs of six do not produce additional costs over four, and (2) targets can be identified faster following externally cued switches compared to internally mediated switches. We then show that these behavioral effects are associated with distinct patterns of neural activation. Switches performed after two repeated-level trials preferentially activated the precuneus, while those performed after both four and six activated bilateral inferior parietal cortex and motor hand area. Relative to external switches, internal switches activated the putamen, while both kinds of switch conjointly activated the large-scale network proposed to underlie internal/external switches in nonhierarchical tasks. Our data further clarify the mechanisms mediating hierarchical selection.

Confidence in recognition memory for words: dissociating right prefrontal roles in episodic retrieval

We used event-related functional magnetic resonance imaging (efMRI) to investigate brain regions showing differential responses as a function of confidence in an episodic word recognition task. Twelve healthy volunteers indicated whether their old-new judgments were made with high or low confidence. Hemodynamic responses associated with each judgment were modeled with an "early" and a "late" response function. As predicted by the monitoring hypothesis generated from a previous recognition study [Henson, R. N. A., Rugg, M. D., Shallice, T., Josephs, O., & Dolan, R. J. (1999a). Recollection and familiarity in recognition memory: An event-related fMRI study. Journal of Neuroscience, 19, 3962-3972], a right dorsolateral prefrontal region showed a greater response to correct low- versus correct high-confidence judgements. Several regions, including the precuneus, posterior cingulate, and left lateral parietal cortex, showed greater responses to correct old than correct new judgements. The anterior left and right prefrontal regions also showed an old-new difference, but for these regions the difference emerged relatively later in time. These results further support the proposal that different subregions of the prefrontal cortex subserve different functions during episodic retrieval. These functions are discussed in relation to a monitoring process, which operates when familiarity levels are close to response criterion and is associated with nonconfident judgements, and a recollective process, which is associated with the confident recognition of old words.

Dissociation of mechanisms underlying syllogistic reasoning

A key question for cognitive theories of reasoning is whether logical reasoning is inherently a sentential linguistic process or a process requiring spatial manipulation and search. We addressed this question in an event-related fMRI study of syllogistic reasoning, using sentences with and without semantic content. Our findings indicate involvement of two dissociable networks in deductive reasoning. During content-based reasoning a left hemisphere temporal system was recruited. By contrast, a formally identical reasoning task, which lacked semantic content, activated a parietal system. The two systems share common components in bilateral basal ganglia nuclei, right cerebellum, bilateral fusiform gyri, and left prefrontal cortex. We conclude that syllogistic reasoning is implemented in two distinct systems whose engagement is primarily a function of the presence or absence of semantic content. Furthermore, when a logical argument results in a belief-logic conflict, the nature of the reasoning process is changed by recruitment of the right prefrontal cortex.

"Sculpting the response space"--an account of left prefrontal activation at encoding

Left lateral prefrontal cortex (PFC) is consistently activated in neuroimaging studies of memory encoding. Its role, however, remains unclear. We describe two functional magnetic resonance imaging (fMRI) studies addressing this question. In the first we used a blocked experimental design to explore the effect of repeated encoding of word paired associates. Initial presentation of word pairs was associated with left ventrolateral PFC activation that attenuated with subsequent presentations of the same lists. When well-learned lists were presented with word pairs rearranged, a left PFC activation, greater than that associated with the initial presentation, was observed. In a second experiment, the formation of these associative relationships was explored using an event-related design. Two types of word pairs were presented: closely related (e.g., King...Queen) and distantly related (e.g., Net...Ship). The same region of left PFC was differentially sensitive to these two event-types, showing a greater response for distantly related pairs. We suggest that left PFC activity, at memory encoding, reflects operations necessary to the formation of meaningful associations in the service of optimal learning. A crucial feature of such associative processing lies in selecting appropriate, and inhibiting inappropriate, semantic attributes of the study material.

Brain mechanisms for detecting perceptual, semantic, and emotional deviance

The observation that we note the exceptional over the mundane has been the subject of extensive psychological and electrophysiological analysis in "oddball" paradigms. Whether detection of a sensory oddball reflects the operation of a generic mechanism or, alternatively, mechanisms sensitive to specific attributes of stimulus deviance is unknown. To address this question we used event-related functional MRI (fMRI) to measure neural responses during presentation of nouns, of which a proportion were perceptually, semantically, or emotionally deviant. Oddballs, regardless of deviant attributes and depth of processing, activated right inferior prefrontal and bilateral posterior fusiform cortices. Attribute-specific responses, independent of depth of processing, were evident in bilateral fusiform cortices for perceptual oddballs and left amygdala for emotional oddballs. By contrast, an interaction with depth of processing was evident in left prefrontal cortex for semantic oddballs. We conclude that detection of oddballs reflects the operation of a generic "deviance detection system," involving right prefrontal and fusiform cortices in addition to specific brain regions sensitive to the stimulus attributes that determine the qualitative characteristics of deviance.

Dissociable neural responses in human reward systems

Reward is one of the most important influences shaping behavior. Single-unit recording and lesion studies in experimental animals have implicated a number of regions in response to reinforcing stimuli, in particular regions of the extended limbic system and the ventral striatum. In this experiment, functional neuroimaging was used to assess neural response within human reward systems under different psychological contexts. Nine healthy volunteers were scanned using functional magnetic resonance imaging during the performance of a gambling task with financial rewards and penalties. We demonstrated neural sensitivity of midbrain and ventral striatal regions to financial rewards and hippocampal sensitivity to financial penalties. Furthermore, we show that neural responses in globus pallidus, thalamus, and subgenual cingulate were specific to high reward levels occurring in the context of increasing reward. Responses to both reward level in the context of increasing reward and penalty level in the context of increasing penalty were seen in caudate, insula, and ventral prefrontal cortex. These results demonstrate dissociable neural responses to rewards and penalties that are dependent on the psychological context in which they are experienced.

A functional neuroanatomy of tics in Tourette syndrome

BACKGROUND

Tics are involuntary, brief, stereotyped motor and vocal behaviors often associated with irresistible urges. They are a defining symptom of the classic neuropsychiatric disorder, Tourette syndrome (TS), and constitute an example of disordered human volition. The neural correlates of tics are not well understood and have not been imaged selectively.

METHODS

Event-related [(15)O]H(2)O positron emission tomography techniques combined with time-synchronized audio and videotaping were used to determine the duration of, frequency of, and radiotracer input during tics in each of 72 scans from 6 patients with TS. This permitted a voxel-by-voxel correlational analysis within Statistical Parametric Mapping of patterns of neural activity associated with the tics.

RESULTS

Brain regions in which activity was significantly correlated with tic occurrence in the group included medial and lateral premotor cortices, anterior cingulate cortex, dorsolateral-rostral prefrontal cortex, inferior parietal cortex, putamen, and caudate, as well as primary motor cortex, the Broca's area, superior temporal gyrus, insula, and claustrum. In an individual patient with prominent coprolalia, such vocal tics were associated with activity in prerolandic and postrolandic language regions, insula, caudate, thalamus, and cerebellum, while activity in sensorimotor cortex was noted with motor tics.

CONCLUSIONS

Aberrant activity in the interrelated sensorimotor, language, executive, and paralimbic circuits identified in this study may account for the initiation and execution of diverse motor and vocal behaviors that characterize tics in TS, as well as for the urges that often accompany them. Arch Gen Psychiatry. 2000;57:741-748

Neural responses associated with cue evoked emotional states and heroin in opiate addicts

Ten male opiate addicts, who were current heroin injectors, underwent positron emission tomographic (PET) scanning during exposure to a sequence of six alternating drug related and neutral video cues, on two occasions. After the second scan, each subject received heroin or placebo using a randomised single-blind procedure. This design allowed the investigation of patterns of brain activity during a range of self-reported cue evoked emotional states, both in the presence and absence of heroin. Self-reports of 'urge to use' correlated strongly with increased regional blood flow (rCBF) in the inferior frontal and orbitofrontal cortex target regions of the mesolimbic dopaminergic system, implicated in conditioning and reward. 'Urge to use' was also associated with highly significant increased rCBF in the right pre-cuneus, an area associated with episodic memory retrieval, and in the left insula, implicated in the processing of the emotional components of stimuli. Self-reports of feeling 'high' correlated with rCBF activation in the hippocampus, an area relevant to the acquisition of stimulus-associated reinforcement.

Selective attention to emotional stimuli in a verbal go/no-go task: an fMRI study

Tasks requiring subjects to attend emotional attributes of words have been used to study mood-congruent information processing biases in anxiety and affective disorders. In this study we adapted an emotional go/no-go task, for use with fMRI to assess the neural substrates of focusing on emotional attributes of words in normal subjects. The key findings were that responding to targets defined on the basis of meaning of words compared to targets defined on the basis of perceptual features was associated with response in inferior frontal gyrus and dorsal anterior cingulate. Further, selecting emotional targets, whether happy or sad, was associated with enhanced response in the subgenual cingulate, while happy targets elicited enhanced neural response in ventral anterior cingulate. These findings reaffirm the importance of medial prefrontal regions in normal emotional processing.

How does the brain sustain a visual percept?

Perception involves the processing of sensory stimuli and their translation into conscious experience. A novel percept can, once synthesized, be maintained or discarded from awareness. We used event-related functional magnetic resonance imaging to separate the neural responses associated with the maintenance of a percept, produced by single-image, random-dot stereograms, from the response evoked at the onset of the percept. The latter was associated with distributed bilateral activation in the posterior thalamus and regions in the occipito-temporal, parietal and frontal cortices. In contrast, sustained perception was associated with activation of the pre-frontal cortex and hippocampus. This observation suggests that sustaining a visual percept involves neuroanatomical systems which are implicated in memory function and which are distinct from those engaged during perceptual synthesis.

Neural activity relating to generation and representation of galvanic skin conductance responses: a functional magnetic resonance imaging study

Central feedback of peripheral states of arousal influences motivational behavior and decision making. The sympathetic skin conductance response (SCR) is one index of autonomic arousal. The precise functional neuroanatomy underlying generation and representation of SCR during motivational behavior is undetermined, although it is impaired by discrete brain lesions to ventromedial prefrontal cortex, anterior cingulate, and parietal lobe. We used functional magnetic resonance imaging to study brain activity associated with spontaneous fluctuations in amplitude of SCR, and activity corresponding to generation and afferent representation of discrete SCR events. Regions that covaried with increased SCR included right orbitofrontal cortex, right anterior insula, left lingual gyrus, right fusiform gyrus, and left cerebellum. At a less stringent level of significance, predicted areas in bilateral medial prefrontal cortex and right inferior parietal lobule covaried with SCR. Generation of discrete SCR events was associated with significant activity in left medial prefrontal cortex, bilateral extrastriate visual cortices, and cerebellum. Activity in right medial prefrontal cortex related to afferent representation of SCR events. Activity in bilateral medial prefrontal lobe, right orbitofrontal cortex, and bilateral extrastriate visual cortices was common to both generation and afferent representation of discrete SCR events identified in a conjunction analysis. Our results suggest that areas implicated in emotion and attention are differentially involved in generation and representation of peripheral SCR responses. We propose that this functional arrangement enables integration of adaptive bodily responses with ongoing emotional and attentional states of the organism.

Neural consequences of competing stimuli in both visual hemifields: a physiological basis for visual extinction

We used positron emission tomography in healthy volunteers to test hemispheric rivalry theories for normal and pathological spatial attention, which provide an influential account of contralesional extinction on bilateral stimulation after unilateral brain injury. Subjects reported visual characters presented either unilaterally or bilaterally. An extinction-like pattern was found behaviorally, with characters in one hemifield reported less accurately when competing characters appeared in the other hemifield. Differences in neural activity for unilateral minus bilateral conditions revealed greater activation of striate and extrastriate areas for stimuli presented without competing stimuli in the other hemifield. Thus, simultaneous bilateral stimulation led to a significant reduction in response by spatiotopic visual cortex contralateral to a particular stimulus. These data provide physiological support for interhemispheric rivalry in the intact human brain, and demonstrate that such competition impacts at early levels of perceptual processing.

Classical fear conditioning in functional neuroimaging

Classical conditioning, the simplest form of associative learning, is one of the most studied paradigms in behavioural psychology. Since the formal description of classical conditioning by Pavlov, lesion studies in animals have identified a number of anatomical structures involved in, and necessary for, classical conditioning. In the 1980s, with the advent of functional brain imaging techniques, particularly positron emission tomography (PET), it has been possible to study the functional anatomy of classical conditioning in humans. The development of functional magnetic resonance imaging (fMRI)--in particular single-trial or event-related fMRI--has now considerably advanced the potential of neuroimaging for the study of this form of learning. Recent event-related fMRI and PET studies are adding crucial data to the current discussion about the putative role of the amygdala in classical fear conditioning in humans.

Dissociable functions in the medial and lateral orbitofrontal cortex: evidence from human neuroimaging studies

Recent imaging studies show that the orbitofrontal cortex (OFC) is activated during a wide variety of paradigms, including guessing tasks, simple delayed matching tasks and sentence completion. We suggest that, as with other regions of the prefrontal cortex, activity in the OFC is most likely to be observed when there is insufficient information available to determine the appropriate course of action. In these circumstances the OFC, rather than other prefrontal regions, is more likely to be activated when the problem of what to do next is best solved by taking into account the likely reward value of stimuli and responses, rather than their identity or location. We suggest that selection of stimuli on the basis of their familiarity and responses on the basis of a feeling of 'rightness' are also examples of selection on the basis of reward value. Within the OFC, the lateral regions are more likely to be involved when the action selected requires the suppression of previously rewarded responses.

Dissociable temporal lobe activations during emotional episodic memory retrieval

The richness of human recollective experience is, in part, related to evocation of previously experienced emotions. An extensive functional neuroimaging literature has provided a description of brain regions involved in retrieving emotionally neutral episodic memories. Whether similar or distinct systems are involved in retrieving emotional memories is unresolved. This question motivated the present functional neuroimaging study, using 0-15 positron emission tomography (PET), where we compared patterns of brain activation associated with retrieving previously studied emotional and neutral pictorial material. By varying task requirements and item density we characterized two distinct neural response patterns during emotional memory retrieval. First, we identified an anterior temporal pole activation that reflected the psychological set associated with emotional memory retrieval. Second, we identified a left amygdala response sensitive to actual retrieval of emotional items. These data suggest distinct functional roles for temporal lobe regions during emotional memory retrieval involving context-related tonic anterior temporal pole activation and a phasic item-related amygdala response. We conclude that brain regions involved in episodic memory retrieval reflect not only physical attributes of stimulus material, for example, their verbal or visual qualities, but also their affective significance.

The role of the right anterior prefrontal cortex in episodic retrieval

Regional brain activity was measured with H(2) (15)O PET while participants attempted to complete word-stem and word-fragment retrieval cues with previously studied words. The retrieval cue manipulation was employed to gain control over the monitoring operations associated with evaluating the episodic status of alternative cue completions. These operations were more constrained for fragments, which had fewer possible completions than each corresponding stem. In one condition (zero target), during the scanning interval none of the cues could be completed with studied items, whereas in another condition (high target), 80% of cues belonged to studied items. Relative to baseline tasks, right anterior prefrontal activity was greater for stems than for fragments in the zero target condition. The target density manipulation did not modulate right anterior prefrontal activity, but was associated with increased activity in right dorsolateral prefrontal cortex. These findings are consistent with the proposal that the right anterior prefrontal cortex supports monitoring operations during episodic retrieval tasks. In addition, the findings add to evidence suggesting that the dorsolateral and anterior right prefrontal cortex make functionally distinct contributions to episodic retrieval.

Cerebral correlates of autonomic cardiovascular arousal: a functional neuroimaging investigation in humans

1. States of peripheral autonomic arousal accompany emotional behaviour, physical exercise and cognitive effort, and their central representation may influence decision making and the regulation of social and emotional behaviours. However, the cerebral functional neuroanatomy representing and mediating peripheral autonomic responses in humans is poorly understood. 2. Six healthy volunteer subjects underwent H215O positron emission tomography (PET) scanning while performing isometric exercise and mental arithmetic stressor tasks, and during corresponding control tasks. Mean arterial blood pressure (MAP) and heart rate (HR) were monitored during scanning. 3. Data were analysed using statistical parametric mapping (SPM99). Conjunction analyses were used to determine significant changes in regional cerebral blood flow (rCBF) during states of cardiovascular arousal common to both exercise and mental stressor tasks. 4. Exercise and mental stressor tasks, relative to their control tasks, were associated with significantly (P < 0.001) increased MAP and HR. Significant common activations (increased rCBF) were observed in cerebellar vermis, brainstem and right anterior cingulate. In both exercise and mental stress tasks, increased rCBF in cerebellar vermis, right anterior cingulate and right insula covaried with MAP; rCBF in pons, cerebellum and right insula covaried with HR. Cardiovascular arousal in both categorical and covariance analyses was associated with decreased rCBF in prefrontal and medial temporal regions. 5. Neural responses in discrete brain regions accompany peripheral cardiovascular arousal. We provide evidence for the involvement of areas previously implicated in cognitive and emotional behaviours in the representation of peripheral autonomic states, consistent with a functional organization that produces integrated cardiovascular response patterns in the service of volitional and emotional behaviours.

Anatomical segregation of component processes in an inductive inference task

Inductive inference underlies much of human cognition. The essential component of induction is hypothesis selection based on some criterion of relevance. The purpose of this study was to determine the neural substrate of inductive inference, particularly hypothesis selection, using fMRI. Ten volunteers were shown stimuli consisting of novel animals under two task conditions, and asked to judge whether all the animals in the set were the same type of animal. In one condition, subjects were given a rule that specified the criteria for "same type of animal". In the other condition, subjects had to infer the rule without instruction. The two conditions were further factored into easy and difficult components. Rule inference was specifically associated with bilateral hippocampal activation while the task by difficulty interaction was associated with activation in right lateral orbital prefrontal cortex. We interpret the former in terms of semantic encoding of novel stimuli and the latter in terms of hypothesis selection. Thus, we show an anatomical dissociation between task implementation and task difficulty that may correspond to a critical psychological distinction in the processes necessary for inductive inference.

Amygdala-hippocampal involvement in human aversive trace conditioning revealed through event-related functional magnetic resonance imaging

Previous functional neuroimaging studies have characterized brain systems mediating associative learning using classical delay conditioning paradigms. In the present study, we used event-related functional magnetic resonance imaging to characterize neuronal responses mediating aversive trace conditioning. During conditioning, neutral auditory tones were paired with an aversive sound [unconditioned stimulus (US)]. We compared neuronal responses evoked by conditioned (CS+) and nonconditioned (CS-) stimuli in which a 50% pairing of CS+ and the US enabled us to limit our analysis to responses evoked by the CS+ alone. Differential responses (CS+ vs CS-), related to conditioning, were observed in anterior cingulate and anterior insula, regions previously implicated in delay fear conditioning. Differential responses were also observed in the amygdala and hippocampus that were best characterized with a time x stimulus interaction, indicating rapid adaptation of CS+-specific responses in medial temporal lobe. These results are strikingly similar to those obtained with a previous delay conditioning experiment and are in accord with a preferential role for medial temporal lobe structures during the early phase of conditioning. However, an additional activation of anterior hippocampus in the present experiment supports a view that its role in trace conditioning is to maintain a memory trace between the offset of the CS+ and the delayed onset of the US to enable associative learning in trace conditioning.