Showing papers by "Raymond J. Dolan published in 1999"
TL;DR: In this article, the authors used measures of right amygdala neural activity acquired from volunteer subjects viewing masked fear-conditioned faces to determine whether a colliculo-pulvinar pathway was engaged during processing of these unseen target stimuli.
Abstract: Neuroimaging studies have shown differential amygdala responses to masked (“unseen”) emotional stimuli. How visual signals related to such unseen stimuli access the amygdala is unknown. A possible pathway, involving the superior colliculus and pulvinar, is suggested by observations of patients with striate cortex lesions who show preserved abilities to localize and discriminate visual stimuli that are not consciously perceived (“blindsight”). We used measures of right amygdala neural activity acquired from volunteer subjects viewing masked fear-conditioned faces to determine whether a colliculo-pulvinar pathway was engaged during processing of these unseen target stimuli. Increased connectivity between right amygdala, pulvinar, and superior colliculus was evident when fear-conditioned faces were unseen rather than seen. Right amygdala connectivity with fusiform and orbitofrontal cortices decreased in the same condition. By contrast, the left amygdala, whose activity did not discriminate seen and unseen fear-conditioned targets, showed no masking-dependent changes in connectivity with superior colliculus or pulvinar. These results suggest that a subcortical pathway to the right amygdala, via midbrain and thalamus, provides a route for processing behaviorally relevant unseen visual events in parallel to a cortical route necessary for conscious identification.
1,267 citations
TL;DR: Functional neuroimaging results provide evidence for dissociable, but interlocking, systems for the processing of distinct categories of negative facial expression.
Abstract: Previous neuroimaging and neuropsychological studies have investigated the neural substrates which mediate responses to fearful, disgusted and happy expressions. No previous studies have investigated the neural substrates which mediate responses to sad and angry expressions. Using functional neuroimaging, we tested two hypotheses. First, we tested whether the amygdala has a neural response to sad and/or angry facial expressions. Secondly, we tested whether the orbitofrontal cortex has a specific neural response to angry facial expressions. Volunteer subjects were scanned, using PET, while they performed a sex discrimination task involving static grey-scale images of faces expressing varying degrees of sadness and anger. We found that increasing intensity of sad facial expression was associated with enhanced activity in the left amygdala and right temporal pole. In addition, we found that increasing intensity of angry facial expression was associated with enhanced activity in the orbitofrontal and anterior cingulate cortex. We found no support for the suggestion that angry expressions generate a signal in the amygdala. The results provide evidence for dissociable, but interlocking, systems for the processing of distinct categories of negative facial expression.
1,222 citations
TL;DR: It is suggested that the responses of different brain regions do dissociate according to the phenomenology associated with memory retrieval, and both R and K judgments for studied words and N judgments for unstudied words were associated with enhanced responses.
Abstract: The question of whether recognition memory judgments with and without recollection reflect dissociable patterns of brain activity is unresolved. We used event-related, functional magnetic resonance imaging (fMRI) of 12 healthy volunteers to measure hemodynamic responses associated with both studying and recognizing words. Volunteers made one of three judgments to each word during recognition: whether they recollected seeing it during study (R judgments), whether they experienced a feeling of familiarity in the absence of recollection (K judgments), or whether they did not remember seeing it during study (N judgments). Both R and K judgments for studied words were associated with enhanced responses in left prefrontal and left parietal cortices relative to N judgments for unstudied words. The opposite pattern was observed in bilateral temporoccipital regions and amygdalae. R judgments for studied words were associated with enhanced responses in anterior left prefrontal, left parietal, and posterior cingulate regions relative to K judgments. At study, a posterior left prefrontal region exhibited an enhanced response to words subsequently given R versus K judgments, but the response of this region during recognition did not differentiate R and K judgments. K judgments for studied words were associated with enhanced responses in right lateral and medial prefrontal cortex relative to both R judgments for studied words and N judgments for unstudied words, a difference we attribute to greater monitoring demands when memory judgments are less certain. These results suggest that the responses of different brain regions do dissociate according to the phenomenology associated with memory retrieval.
832 citations
TL;DR: The findings of this study support an hypothesis that emotion and attention modulate both early and late stages of visual processing.
485 citations
TL;DR: This functional MRI study of 12 healthy volunteers tested the hypothesis that one role of the right prefrontal cortex is to monitor the information retrieved from episodic memory in order to make an appropriate response.
Abstract: Though the right prefrontal cortex is often activated in neuroimaging studies of episodic memory retrieval, the functional significance of this activation remains unresolved In this functional MRI study of 12 healthy volunteers, we tested the hypothesis that one role of the right prefrontal cortex is to monitor the information retrieved from episodic memory in order to make an appropriate response The critical comparison was between two word recognition tasks that differed only in whether correct responses did or did not require reference to the spatiotemporal context of words presented during a previous study episode Activation in a dorsal midlateral region of the right prefrontal cortex was associated with increased contextual monitoring demands, whereas a more ventral region of the right prefrontal cortex showed retrieval-related activation that was independent of task instructions This functional dissociation of dorsal and ventral right prefrontal regions is discussed in relation to a theoretical framework for the control of episodic memory retrieval
467 citations
TL;DR: A direct comparison of studies 1 and 3 confirmed that a ventral right lateral prefrontal region is primarily activated by discrepancies between signals from sensory systems, while a more dorsal area inright lateral prefrontal cortex is activated when actions must be maintained in the face of a conflict between intention and sensory outcome.
Abstract: Normal sensorimotor states involve integration of intention, action and sensory feedback. An example is the congruence between motor intention and sensory experience (both proprioceptive and visual) when we move a limb through space. Such goal-directed action necessitates a mechanism that monitors sensorimotor inputs to ensure that motor outputs are congruent with current intentions. Monitoring in this sense is usually implicit and automatic but becomes conscious whenever there is a mismatch between expected and realized sensorimotor states. To investigate how the latter type of monitoring is achieved we conducted three fully factorial functional neuroimaging experiments using PET measures of relative regional cerebral blood flow with healthy volunteers. In the first experiment subjects were asked to perform Luria's bimanual co-ordination task which involves either in-phase (conditions 1 and 3) or out-of-phase (conditions 2 and 4) bimanual movements (factor one), while looking towards their left hand. In half of the conditions (conditions 3 and 4) a mirror was used that altered visual feedback (factor two) by replacing their left hand with the mirror image of their right hand. Hence (in the critical condition 4) subjects saw in-phase movements despite performing out-of-phase movements. This mismatch between intention, proprioception and visual feedback engendered cognitive conflict. The main effect of out-of-phase movements was associated with increased neural activity in posterior parietal cortex (PPC) bilaterally [Brodmann area (BA) 40, extending into BA 7] and dorsolateral prefrontal cortex (DLPFC) bilaterally (BA 9/46). The main effect of the mirror showed increased neural activity in right DLPFC (BA 9/46) and right superior PPC (BA 7) only. Analysis of the critical interaction revealed that the mismatch condition led to a specific activation in the right DLPFC alone (BA 9/46). Study 2, using an identical experimental set-up but manipulating visual feedback from the right hand (instead of the left), subsequently demonstrated that this right DLPFC activation was independent of the hand attended. Finally, study 3 removed the motor intentional component by moving the subjects' hand passively, thus engendering a mismatch between proprioception and vision only. Activation in the right lateral prefrontal cortex was now more ventral than in studies 1 or 2 (BA 44/45). A direct comparison of studies 1 and 3 (which both manipulated visual feedback from the left hand) confirmed that a ventral right lateral prefrontal region is primarily activated by discrepancies between signals from sensory systems, while a more dorsal area in right lateral prefrontal cortex is activated when actions must be maintained in the face of a conflict between intention and sensory outcome.
439 citations
TL;DR: 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.
Abstract: 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.
395 citations
TL;DR: Findings support the role of paralimbic structures as neural substrates of anticipatory anxiety and the failure to demonstrate behavioral and neurophysiological changes with the distractor task may reflect the modest increases in anxiety with the shock, the relatively simple distractionor task, and small sample size.
338 citations
TL;DR: This work measures hippocampal responses to novelty, using functional MRI (fMRI), during an item-learning paradigm generated from an artificial grammar system, and demonstrates a left anterior hippocampal response to both types of novelty and adaptation of these responses with stimulus familiarity.
Abstract: It is now accepted that hippocampal lesions impair episodic memory. However, the precise functional role of the hippocampus in episodic memory remains elusive. Recent functional imaging data implicate the hippocampus in processing novelty, a finding supported by human in vivo recordings and event-related potential studies. Here we measure hippocampal responses to novelty, using functional MRI (fMRI), during an item-learning paradigm generated from an artificial grammar system. During learning, two distinct types of novelty were periodically introduced: perceptual novelty, pertaining to the physical characteristics of stimuli (in this case visual characteristics), and exemplar novelty, reflecting semantic characteristics of stimuli (in this case grammatical status within a rule system). We demonstrate a left anterior hippocampal response to both types of novelty and adaptation of these responses with stimulus familiarity. By contrast to these novelty effects, we also show bilateral posterior hippocampal responses with increasing exemplar familiarity. These results suggest a functional dissociation within the hippocampus with respect to the relative familiarity of study items. Neural responses in anterior hippocampus index generic novelty, whereas posterior hippocampal responses index familiarity to stimuli that have behavioral relevance (i.e., only exemplar familiarity). These findings add to recent evidence for functional segregation within the human hippocampus during learning.
319 citations
TL;DR: For instance, this article employed fMRI to index neural activity in prefrontal cortex during tests of recognition and source memory and found that high density recognition was associated with increased activity in right and, to a lesser extent, left, anterior prefrontal cortex (BA 10), replicating the findings of two previous PET studies.
291 citations
TL;DR: The authors found that bilateral posterior areas in fusiform gyrus responded more strongly for faces with positive than with negative contrast polarity, even though this preserves all edges and spatial frequencies.
Abstract: Functional imaging has revealed face-responsive visual areas in the human fusiform gyrus, but their role in recognizing familiar individuals remains controversial. Face recognition is particularly impaired by reversing contrast polarity of the image, even though this preserves all edges and spatial frequencies. Here, combined influences of familiarity and priming on face processing were examined as contrast polarity was manipulated. Our fMRI results show that bilateral posterior areas in fusiform gyrus responded more strongly for faces with positive than with negative contrast polarity. An anterior, right-lateralized fusiform region is activated when a given face stimulus becomes recognizable as a well-known individual.
TL;DR: An alternative method of data analysis is proposed that emphasizes global integration rather than isolated regional changes in response to psychological tasks, and suggests that brain abnormalities in schizophrenia are best characterized as a disturbance in the integration of activity across a number of brain regions.
TL;DR: Data from this experiment support a model of the serotonergic system in which the habenula projection to the raphé represents a convergent feedback pathway that controls the release of 5-HT throughout the brain.
TL;DR: That processing of vocal emotion involves a bilaterally distributed network of brain regions and that processing of fear-related auditory stimuli involves context-specific interactions between the amygdala and other cortical and brainstem regions implicated in fear processing is demonstrated.
TL;DR: The data suggest that while simple two choice guessing depends on an extensive neural system including regions of the right lateral prefrontal cortex, activation of orbitofrontal cortex increases as the probabilistic contingencies become more complex.
TL;DR: The effect of rule acquisition on neuronal responses associated with explicit learning of individual items was characterized as modulation of the time-dependent right PFC activations such that the early increase in activation associated with item learning was attenuated as the experiment progressed.
Abstract: We assessed time-dependent neuronal activity accompanying learning using functional magnetic resonance imaging (fMRI). An artificial grammar learning paradigm enabled us to dissociate activations associated with individual item learning from those involved in learning the underlying grammar system. We show that a localized region of right prefrontal cortex (PFC) is preferentially sensitive to individual item learning during the early stages of the experiment, while the left PFC region is sensitive to grammar learning which occurred across the entire course of the experiment. In addition to dissociating these two types of learning, we were able to characterize the effect of rule acquisition on neuronal responses associated with explicit learning of individual items. This effect was expressed as modulation of the time-dependent right PFC activations such that the early increase in activation associated with item learning was attenuated as the experiment progressed. In a further analysis we used structural equation modelling to explore time-dependent changes in inter-regional connectivity as a function of both item and grammar rule learning. Although there were no significant effects of item learning on the measured path strengths, rule learning was associated with a decrease in right fronto-parietal connectivity and an increase in connectivity between left and right PFC. Further fronto-parietal path strengths were observed to change, with an increase in left fronto-parietal and a decrease in right fronto-parietal connectivity path strength from right PFC to left parietal cortex. We interpret our findings in terms of a left frontal system mediating the semantic analysis of study items and directly influencing a right fronto-parietal system associated with episodic memory retrieval.
TL;DR: It is concluded that DMTS and DNMTS are not equivalent and furthermore that the precise neural implementation of these tasks is a dynamic function of delay interval.
Abstract: Visual short-term memory in humans and animals is frequently assessed using delayed matching to sample (DMTS) and delayed nonmatching to sample (DNMTS) tasks across variable delay intervals. Although these tasks depend on certain common mechanisms, there are behavioral differences between them, and neuroimaging provides a means of assessing explicitly whether this is underpinned by differences at a neural level. Findings of delay-dependent deficits, after lesions in humans and animals, suggest that the neural implementation of these tasks may also critically depend on the delay interval. In this study we determined whether there were differential neural responses associated with DMTS and DNMTS tasks at two different delay intervals using functional magnetic resonance imaging. Ten healthy volunteers were studied under four test conditions: DMTS and DNMTS at 5 and 15 sec delay. The main effect of DMTS compared with DNMTS across both delay intervals was associated with significant activation in bilateral head of caudate and medial orbitofrontal cortex. By contrast, DNMTS compared with DMTS was associated with significant activation in mediodorsal thalamus, bilateral lateral orbitofrontal cortex, and left premotor cortex. The main effect of short compared with long delay, across both tasks, was associated with significantly greater activity in occipital and parietal cortices. By contrast, long compared with short delay was associated with significantly greater activity in temporal and ventrolateral frontal cortices. We conclude that DMTS and DNMTS are not equivalent and furthermore that the precise neural implementation of these tasks is a dynamic function of delay interval.
TL;DR: The effect of both heroin and heroin‐related visual cues are maximally expressed in the sites of origin of ascending midbrain neuromodulatory systems, which implicate common neurobiological processes underlying drug and drug‐cue‐related effects.
Abstract: The neurobiological mechanisms of opiate addictive behaviour in humans are unknown. A proposed model of addiction implicates ascending brainstem neuromodulatory systems, particularly dopamine. Using functional neuroimaging, we assessed the neural response to heroin and heroin-related cues in established opiate addicts. We show that the effect of both heroin and heroin-related visual cues are maximally expressed in the sites of origin of ascending midbrain neuromodulatory systems. These context-specific midbrain activations predict responses to salient visual cues in cortical and subcortical regions implicated in reward-related behaviour. These findings implicate common neurobiological processes underlying drug and drug-cue-related effects.
TL;DR: Changes in neural activity in distinct brain regions mediate the clinical phenomena of depression and depression-related cognitive impairment following acute tryptophan depletion and could be associated with the widespread distribution of serotonin neurons in brain pathwaysassociated with the expression of affect and cognitive performance.
Abstract: BACKGROUND Acute tryptophan depletion lowers brain serotonin synthesis and results in a transient, but striking, clinical relapse in recovered depressed patients.
AIMS To identify brain regions which change their activity as an acute depressive relapse evolves and to determine how pathological mood might modulate neural activity during a cognitive task.
METHOD We used H2(15)O positron-emission tomography (PET) to study eight recovered depressed men after tryptophan depletion and after a control procedure. During both PET scan sessions, subjects performed a paced verbal fluency task which alternated with a control verbal repetition task.
RESULTS Increasing levels of depression after tryptophan depletion were associated with diminished neural activity in the ventral anterior cingulate, orbitofrontal cortex and caudate nucleus regions. In addition, depressive relapse attenuated cognitive task-related activation in the anterior cingulate cortex.
CONCLUSIONS Our data indicate that changes in neural activity in distinct brain regions mediate the clinical phenomena of depression and depression-related cognitive impairment following acute tryptophan depletion. These changes could be associated with the widespread distribution of serotonin neurons in brain pathways associated with the expression of affect and cognitive performance.
TL;DR: Patients with medial prefrontal lesions often display irresponsible behavior, despite being intellectually unimpaired, but similar lesions occurring in early childhood can also prevent the acquisition of factual knowledge about accepted standards of moral behavior.
Abstract: Patients with medial prefrontal lesions often display irresponsible behavior, despite being intellectually unimpaired. But similar lesions occurring in early childhood can also prevent the acquisition of factual knowledge about accepted standards of moral behavior.
TL;DR: In this article, the functional role of the hippocampus in human episodic memory is examined using fMRI data from a modified artificial grammar learning paradigm, and it is shown that both anterior and posterior hippocampal responses are modulated to the degree to which stimuli can be assimilated into a meaningful rule-based framework.
Abstract: The precise functional role of the hippocampus in human episodic memory is an unresolved question though it has recently been suggested that distinct medial temporal lobe (MTL) regions are involved in encoding and retrieval operations respectively. For example, a recent meta-analysis of positron emission tomography (PET) literature has suggested a rostral-caudal functional division in the medial temporal lobes (MTL), with rostral MTL mediating encoding and caudal MTL retrieval operations. However, a review of the combined PET and fMRI literature, reported in the present issue, while noting systematic discrepancies between PET and fMRI, reaches a conclusion that posterior MTL is involved in encoding. Here we present fMRI data, from a modified artificial grammar learning paradigm, that examines two questions concerning the functional role of the hippocampus, and related MTL structures in episodic memory. Firstly, we test a hypothesis that anterior hippocampus is activated during encoding and that this response is greater for novel items. Secondly, we test whether increasing familiarity with stimulus material is associated with a posterior MTL neural response. Our empirical findings support both hypotheses in that we demonstrate a left anterior hippocampal response sensitive to encoding demands and a posterior parahippocampal response sensitive to retrieval demands. Furthermore, we show that both anterior and posterior hippocampal responses are modulated to the degree to which stimuli can be assimilated into a meaningful rule-based framework. Hippocampus 1999;9:25-34. (C) 1999 Wiley-Liss, Inc.
Journal Article•
TL;DR: It is suggested that the responses of different brain regions do dissociate according to the phenomenology associated with memory retrieval, as seen in hemodynamic responses associated with both studying and recognizing words.
Abstract: The question of whether recognition memory judgments with
and without recollection reflect dissociable patterns of brain activity is unresolved. We used event-related, functional magnetic resonance imaging (fMRI) of 12 healthy volunteers to measure hemodynamic responses associated with both studying and recognizing words. Volunteers made one of three judgments to each word during recognition: whether they recollected seeing it during study (R judgments), whether they experienced a feeling of familiarity in the absence of recollection(K judgments), or whether they did not remember seeing it during study (N judgments). Both R and K judgments for studied words were associated with enhanced responses in left prefrontal and left parietal cortices relative to N judgments for unstudied words. The opposite pattern was observed in bilateral temporoccipital regions and amygdalae. R judgments for studied words were associated with enhanced responses in anterior left prefrontal, left parietal, and posterior cingulate regions relative to K judgments. At study, a posterior left prefrontal region exhibited an enhanced response to words subsequently given R versus K judgments, but the response of this region during recognition did not differentiate R and K judgments. K judgments for studied words were associated with enhanced responses in right lateral and medial prefrontal cortex relative to both R judgments for studied words and N judgments for unstudied words, a difference we attribute to greater monitoring demands when memory judgments are less certain.
These results suggest that the responses of different brain
regions do dissociate according to the phenomenology associated with memory retrieval.
Abstract: A striking feature of schizophrenia is the diversity of the phenomenology both within and between patients. This diversity can be contrasted with the well-circumscribed and stable deficits seen in classic neuropsychological syndromes. The argument will be advanced that the classic lesion model, based on the notion of a segregated deficit, is inappropriate in schizophrenia. Instead the idea will be developed that a more appropriate model is one derived from concepts of neural integration across large-scale brain networks. Empirical data derived from positron emission tomography (PET) within our laboratory that provide support for this suggestion will be presented. One critical observation from these data is a disruption of prefrontal-temporal interactions, under a variety of cognitive activation paradigms, in both chronic medicated and acute unmedicated schizophrenic patients. Furthermore, these data indicate that both regional and interregional neuronal function, including prefrontal-temporal interactions, can be significantly modulated by a neurochemical perturbation of ascending dopaminergic systems. The latter observations suggest that the deficit of abnormal cortico-cortical interactions are to some extent modifiable by neuromodulatory neurotransmitter systems.
TL;DR: The effects of diazepam on ordering tasks are not simply secondary to diazepAM effects on episodic memory, but reflect real and distinct effects of the drug on executive function.
Abstract: Rationale: Diazepam and other benzodiazepines impair episodic memory encoding. Deficits in tests of executive function are also reported. In this study, we ask whether the latter effects are secondary to mnemonic impairment, or reflect specific and distinct effects of benzodiazepines on executive function. Objectives: Using positron emission tomography in healthy human volunteers, we examined similarities in the neuroanatomical correlates of the effect of diazepam on performance of executive compared to episodic memory tasks. Close similarities are proposed to reflect commonalities in the functional effects of the drug. Conversely, any evidence of task-specific regional changes in activity is proposed to reflect distinct functional effects of DZP on the two tasks. Methods: Twelve volunteers received placebo or 10 mg diazepam in a between-subjects design. During scanning, subjects performed one of four experimental conditions, corresponding to a 2×2 factorial design, with memory encoding and executive function (on-line ordering of stimuli) as the two factors. Drug- or task-induced changes in brain activation indexed the neuroanatomical correlates of each condition. Results: Averaged across all conditions, and compared to placebo, diazepam decreased activity bilaterally in prefrontal and temporal cortices. Within this network of deactivation, left dorsal prefrontal cortex activity was attenuated by diazepam during memory encoding, while left frontal opercular activity was attenuated during ordering. Conclusion: This neuroanatomical dissociation reflects distinct functional effects of diazepam on encoding versus ordering tasks. Therefore, the effects of diazepam on ordering tasks are not simply secondary to diazepam effects on episodic memory, but reflect real and distinct effects of the drug on executive function.
TL;DR: Recent evidence suggests that the functions of the brain region critical for long-term memory, the hippocampus, may be segregated along its anterior-posterior axis.
Abstract: Recent evidence suggests that the functions of the brain region critical for long-term memory, the hippocampus, may be segregated along its anterior-posterior axis.
TL;DR: The self may be defined in terms of responses to experience as mentioned in this paper, and the self may also be defined as a response to the experience of the experience itself, i.e.
Abstract: The self may be defined in terms of responses to experience.
TL;DR: It is demonstrated that the response in right ventrolateral PFC is preferentially sensitive to a condition in which all material was familiar, which suggests that sensitivity to stimulus familiarity is expressed in right PFC, even within the context of an encoding task.
Abstract: In a previous word-pair encoding study (Dolan & Fletcher, 1997), we examined the effect of introducing novelty, either in studied words or in their mutual associations. A left medial temporal lobe (MTL) sensitivity to novel words and left prefrontal cortex (PFC) to novel associations was observed. In this further report on the data, we explored the extent to which the right PFC, more generally implicated in retrieval operations (Fletcher, Frith, & Rugg, 1997), was sensitive to these manipulations. Specifically, we characterised changes associated with increasing familiarity of study material. We demonstrate that the response in right ventrolateral PFC is preferentially sensitive to a condition in which all material was familiar (that is, in which all material had been presented prior to scanning). A more dorsal region in right PFC was found to be relatively more active in association with a condition in which one item in the pair was familiar but was paired with a novel associate. Our results suggest that sensitivity to stimulus familiarity is expressed in right PFC, even within the context of an encoding task. The data also provide further evidence for functional heterogeneity within right PFC, with a more ventral region responding to familiarity of complete word pairs and a more dorsal region responding to familiar single words occurring in the context of new associative relationships.
01 Jan 1999