Biomedical subjects

Richard N A Henson

Publications and source records attributed to Richard N A Henson.

15 recordsLinked to original sources

PubMed2007

Separate coding of different gaze directions in the superior temporal sulcus and inferior parietal lobule.

Electrophysiological recording in the anterior superior temporal sulcus (STS) of monkeys has demonstrated separate cell populations responsive to direct and averted gaze. Human functional imaging has demonstrated posterior STS activation in gaze processing, particularly in coding the intentions conveyed by gaze, but to date has provided no evidence of dissociable coding of different gaze directions. Because the spatial resolution typical of group-based fMRI studies (approximately 6-10 mm) exceeds the size of cellular patches sensitive to different facial characteristics (1-4 mm in monkeys), a more sensitive technique may be required. We therefore used fMRI adaptation, which is considered to offer superior resolution, to investigate whether the human anterior STS contains representations of different gaze directions, as suggested by non-human primate research. Subjects viewed probe faces gazing left, directly ahead, or right. Adapting to leftward gaze produced a reduction in BOLD response to left relative to right (and direct) gaze probes in the anterior STS and inferior parietal cortex; rightward gaze adaptation produced a corresponding reduction to right gaze probes. Consistent with these findings, averted gaze in the adapted direction was misidentified as direct. Our study provides the first human evidence of dissociable neural systems for left and right gaze.

Adaptation, Physiological↗

PubMed2006

Perirhinal cortex activity during visual object discrimination: an event-related fMRI study.

Previous fMRI studies have demonstrated preferential involvement of the perirhinal cortex and hippocampus in tasks of object and spatial memory, respectively. Here we investigated whether similar activity would also be present when object and spatial discrimination was assessed in the absence of explicit declarative memory demands. On each trial in the scanner, participants were presented simultaneously with two arrays of objects and were asked to indicate whether both arrays were identical, differed with respect to the identity of one object or differed with respect to the spatial arrangement of the objects. It was found that the detection of an object identity change was associated with significant right perirhinal cortex activity. We suggest that this perirhinal activity indicates a role of this structure in processes beyond declarative memory, for example, short-term visual working memory or higher order perception. Significantly greater hippocampal activity was not, however, observed during the spatial arrangement condition, perhaps due to the relatively low spatial processing demands of this task.

Adolescent↗

PubMed2006

fMRI correlates of retrieval orientation.

Processes related to the cueing of memory retrieval were investigated using fMRI during a yes/no recognition memory test. Participants studied either pictures or auditory words and were subsequently tested with visual words that either corresponded to studied items (old items) or were unstudied (new items). It was expected that neural activity would differ according to the type of information participants are trying to retrieve: a manifestation of the so-called "retrieval orientation" effect. We replicated robust old/new effects in parietal, prefrontal and anterior medial temporal lobe cortices, which did not differ according to the study material. However, we did observe differential activity to test items in temporoparietal cortex and fusiform cortex as a function of the study material. More specifically, attempts to retrieve words encoded auditorily produced greater activity in auditory cortex than attempts to retrieve words encoded as pictures, whereas the converse was found in fusiform cortex. The above pattern was found for both new and old test items. These findings implicate these regions in constraining the search for specific types of encoded information and thus are in accordance with the transfer-appropriate processing framework. Further, we propose that our results can be seen as an extension of the cortical reinstatement hypothesis, in that the same material-specific cortical regions are engaged during both encoding and retrieval, and this increases the likelihood of successful recognition, or rejection, of retrieval cues in a memory test.

Acoustic Stimulation↗

PubMed2006

Neuroanatomical dissociation of encoding processes related to priming and explicit memory.

Priming is a facilitation of cognitive processing with stimulus repetition that can occur without explicit memory. Whereas the functional neuroanatomy of perceptual priming at retrieval is established, encoding processes that initiate priming and explicit memory have not yet been anatomically separated, and we investigated them using event-related functional magnetic resonance imaging. Activations predicting later explicit memory occurred in the bilateral medial temporal lobe (MTL) and left prefrontal cortex (PFC). Activity predicting later priming did not occur in these areas, but rather in the bilateral extrastriate cortex, left fusiform gyrus, and bilateral inferior PFC, areas linked with stimulus identification. Surprisingly, these regions showed response reductions. Our results demonstrate that priming and explicit memory have distinct functional neuroanatomies at encoding, with MTL activations being specific for explicit memory, and suggest that priming is initiated by sharpness of neural responding in stimulus identification areas, consistent with recent electrophysiological evidence regarding priming-related neural oscillations at encoding. We tentatively suggest that this sharpened responding at encoding may set the stage for increased neural processing efficiency at retrieval, with these different neural mechanisms both leading to observed priming-related hemodynamic decreases, and argue that neural measurements at encoding, and not just at retrieval, will be critical in resolving the debate about the neural mechanisms of learning that underlie priming.

Adolescent↗

PubMed2006

ERP correlates of retrieval orientation: direct versus indirect memory tasks.

The neural correlates of the processes involved in cueing memory retrieval were investigated using ERPs to unstudied (new) items in a yes/no recognition test (direct memory task) and a semantic judgement task (indirect memory task). Subjects encoded either pictures or auditory words and were tested on visual words. We replicated previous findings that ERPs to correct rejections of new items in a yes/no recognition test differ according to the study material, with ERPs to words encoded as pictures being more negative (relative to a average mastoid reference) than words encoded auditorily [Hornberger, M., Morcom, A.M., et al., 2004. Neural correlates of retrieval orientation: effects of study-test similarity. J. Cogn. Neurosci. 16 (7), 1196-1210]. This difference was sustained from approximately 450-1,200 ms. An effect of study material on the ERP to new items was found in the indirect memory task but was both earlier onsetting and shorter lived, ca. 250-600 ms. These findings add weight to the concept of 'retrieval orientation' [Rugg, M.D., Wilding, E.L., 2000. Retrieval processing and episodic memory. Trends Cogn. Sci. 4 (3) 108-115] - differential processing of retrieval cues according to the form of the sought-for information - by showing that a putative ERP correlate of retrieval orientation is restricted to direct memory tasks.

Acoustic Stimulation↗

PubMed2006

On the status of unconscious memory: Merikle and Reingold (1991) revisited.

Four experiments are reported that reevaluate P. M. Merikle and E. M. Reingold's (1991) demonstration of unconscious memory: the greater sensitivity to familiarity (repetition) of an indirect (implicit) memory task than of a comparable direct (explicit) task. At study, participants named the cued member of a pair of visually presented words. At test, new and uncued study words were presented against a background mask. Participants judged whether each word was old or new (direct task) or whether the contrast between the word and the background was high or low (indirect task). Contrary to the original findings, the sensitivity of the indirect task to familiarity never exceeded that of the direct task. These findings pose a challenge to a key pillar of evidence for unconscious influences of memory.

Adolescent↗

PubMed2005

Further dissociating the processes involved in recognition memory: an FMRI study.

Based on an event-related potential study by Rugg et al. [Dissociation of the neural correlates of implicit and explicit memory. Nature, 392, 595-598, 1998], we attempted to isolate the hemodynamic correlates of recollection, familiarity, and implicit memory within a single verbal recognition memory task using event-related fMRI. Words were randomly cued for either deep or shallow processing, and then intermixed with new words for yes/no recognition. The number of studied words was such that, whereas most were recognized ("hits"), an appreciable number of shallow-studied words were not ("misses"). Comparison of deep hits versus shallow hits at test revealed activations in regions including the left inferior parietal gyrus. Comparison of shallow hits versus shallow misses revealed activations in regions including the bilateral intraparietal sulci, the left posterior middle frontal gyrus, and the left frontopolar cortex. Comparison of hits versus correct rejections revealed a relative deactivation in an anterior left medial-temporal region (most likely the perirhinal cortex). Comparison of shallow misses versus correct rejections did not reveal response decreases in any regions expected on the basis of previous imaging studies of priming. Given these and previous data, we associate the left inferior parietal activation with recollection, the left anterior medial-temporal deactivation with familiarity, and the intraparietal and prefrontal responses with target detection. The absence of differences between shallow misses and correct rejections means that the hemodynamic correlates of implicit memory remain unclear.

Adolescent↗

PubMed2004

Morphing Marilyn into Maggie dissociates physical and identity face representations in the brain.

How the brain represents different aspects of faces remains controversial. Here we presented subjects with stimuli drawn from morph continua between pairs of famous faces. In the paired presentations, a second face could be identical to the first, could share perceived identity but differ physically (30% along the morph continuum), or could differ physically by the same distance along the continuum (30%) but in the other direction. We show that, behaviorally, subjects are more likely to classify face pairs in the third paired presentation as different and that this effect is more pronounced for subjects who are more familiar with the faces. In functional magnetic resonance imaging (fMRI), inferior occipital gyrus (IOG) shows sensitivity to physical rather than to identity changes, whereas right fusiform gyrus (FFG) shows sensitivity to identity rather than to physical changes. Bilateral anterior temporal regions show sensitivity to identity change that varies with the subjects' pre-experimental familiarity with the faces. These findings provide neurobiological support for a hierarchical model of face perception.

Adult↗

PubMed2004

Probability effects on the neural correlates of retrieval success: an fMRI study.

Event-related fMRI was employed to investigate the influence of the relative probability of old and new test items on the neural correlates of recognition memory. Twelve subjects undertook three study-test cycles, each consisting of an identical study phase in which a series of words was encoded in an incidental task, followed by a test phase in which yes/no recognition judgments were made to a mixture of studied (old) and unstudied (new) words. The ratio of old to new words differed in each test phase, and was either 25:75, 50:50, or 75:25. In lateral inferior and medial parietal cortex, and the posterior cingulate, greater activity was elicited by correctly classified old than new items independently of old:new ratio. By contrast, in other regions, including anterior, dorsolateral, and ventrolateral prefrontal cortex, differences in the activity elicited by old and new items varied according to old:new ratio, demonstrating in some cases a complete crossover interaction. The results suggest that differential activity elicited by old and new test items is likely to support successful recognition in only a subset of the regions identified in previous studies as exhibiting such differences. In other regions, most notably prefrontal cortex, differences in the activity elicited by old and new items appear to reflect processes that are contingent upon, rather than in support of, successful recognition.

Adolescent↗

PubMed2003

Neural correlates of retrieval processing in the prefrontal cortex during recognition and exclusion tasks.

Event-related fMRI was employed to contrast the neural activity elicited in prefrontal cortex during recognition memory and exclusion tests. The study phases preceding each memory test were identical, involving the presentation of study items (visually presented words) in one of two study contexts. For the recognition test subjects were required to respond positively to all old items regardless of study context, and to respond negatively to new items. For the exclusion task, positive responses were required to old items presented in one of the study contexts only; negative responses were required both to unstudied items and studied items from the alternative context (non-targets). No prefrontal region demonstrated greater activity for new items in the exclusion task. Thus, there was no evidence that retrieval cues were processed differently according to the specificity of the sought-for information. In several regions, most notably bilateral anterior prefrontal cortex, activity was greater for old than for new items regardless of task. Activity in right dorsolateral prefrontal cortex was also greater for old than for new items; these effects however were larger in the exclusion task. The findings are consistent with previous reports that activity in anterior prefrontal cortex elicited by recognition retrieval cues is sensitive to retrieval success, and extend these findings to the exclusion task. The findings for the right dorsolateral cortex add further weight to the proposal that this region supports post-retrieval monitoring of retrieved information.

Adult↗

PubMed2002

The neural basis of episodic memory: evidence from functional neuroimaging.

We review some of our recent research using functional neuroimaging to investigate neural activity supporting the encoding and retrieval of episodic memories, that is, memories for unique events. Findings from studies of encoding indicate that, at the cortical level, the regions responsible for the effective encoding of a stimulus event as an episodic memory include some of the regions that are also engaged to process the event 'online'. Thus, it appears that there is no single cortical site or circuit responsible for episodic encoding. The results of retrieval studies indicate that successful recollection of episodic information is associated with activation of lateral parietal cortex, along with more variable patterns of activity in dorsolateral and anterior prefrontal cortex. Whereas parietal regions may play a part in the representation of retrieved information, prefrontal areas appear to support processes that act on the products of retrieval to align behaviour with the demands of the retrieval task.

Brain Mapping↗

PubMed2002

The effects of interdistracter similarity on search processes in superior parietal cortex.

The superior parietal lobe has been associated with the spatial integration of visual features, an important step in the detection of particular form conjunctions. However, behavioral research has indicated that when target items can be segmented from neighboring distracters via similarity grouping, detection may not rely on spatial integration. The question therefore arises as to whether the superior parietal cortex is an integral component of conjunction search or only important in the absence of certain grouping relations. Here, we acquired measures of reaction time and event-related fMRI, while subjects searched for conjunction targets in displays containing either homogeneous or heterogeneous distracters. We confirm that under conditions of low distracter similarity, search involves parietal-motor areas associated with spatial selection. However, we also demonstrate that under conditions of high distracter similarity, search is instead associated with activation of right temporal-parietal cortex. These results suggest that the superior parietal cortex is not a necessary component of visual conjunction search and highlight a new role for the right temporal-parietal cortex in perceptual grouping.

Adult↗

PubMed2002

Scopolamine but not lorazepam modulates face repetition priming: a psychopharmacological fMRI study.

Repetition priming is a basic form of learning associated with decreased neuronal responses following stimulus repetition. In this experiment, we address cholinergic and GABAergic modulation of repetition priming in a face recognition paradigm. In experiment 1, we used event-related functional magnetic resonance imaging (fMRI) in combination with pharmacological challenge where participants were given placebo, lorazepam (2mg po), or scopolamine (0.4 mg IV) prior to study. Behavioral data showed intact priming for famous faces in the placebo and lorazepam group but impaired priming following scopolamine. In within-group analyses, a right fusiform region showed a fame by repetition interaction characterized by a response decrease to repetition of famous faces and a response enhancement to repetition of unfamous faces in the placebo group. In subjects treated with lorazepam, a main effect of repetition, driven by response decreases to repetition of famous faces, was seen in this right fusiform region. No significant repetition effects were found after scopolamine. In experiment 2, we further investigated behaviorally the cholinergic impairment of repetition priming. Participants were given either placebo or scopolamine (0.4 mg IV) after study. Behavioral data showed intact priming for famous faces in the placebo and scopolamine group. The results suggest that scopolamine but not lorazepam impair repetition priming for famous faces in a face recognition paradigm. These cholinergic impairments are likely to reflect interference with acquisition processes during study that may co-occur with a modulation of right fusiform decreases to repetition of famous faces.

Acetylcholine↗

PubMed2002

State-related and item-related neural correlates of successful memory encoding.

Neuroimaging studies show that the efficacy of long-term memory encoding of a stimulus is indexed by transient neural activity elicited by that stimulus. Here, we show that successful memory encoding is also indexed by neural activity that is tonically maintained throughout a study task. Using functional magnetic resonance imaging (fMRI), transient and sustained neural activity were dissociated with a mixed event-related and blocked design. In a series of short task blocks, human subjects made semantic or phonological decisions about visually presented words. After statistically removing item-related activity, we found that the mean level of activity across a task block was correlated with the number of words subsequently remembered from that block. These correlations were found in inferior medial parietal and left prefrontal cortex for the semantic task, and in superior medial parietal cortex for the phonological task. Our findings suggest that state-related activity in these brain regions is involved in memory encoding.

Adolescent↗

PubMedDate not supplied

Modulation of retrieval processing reflects accuracy of emotional source memory.

There is considerable evidence that encoding and consolidation of memory are modulated by emotion, but the retrieval of emotional memories is not well characterized. Here we manipulated the emotional context with which affectively neutral stimuli were associated during encoding, allowing us to examine neural activity associated with retrieval of emotional memories without confounding the emotional attributes of cue items and the retrieved context. Using a source memory procedure we were also able to compare how retrieval processing was modulated when the emotional encoding context was recollected or not. An interaction between emotional encoding context and accuracy of source memory revealed that successful retrieval of emotional context was associated with activity in left amygdala, and a left frontotemporal network including anterior insula, prefrontal cortex and cingulate. In contrast, when contextual retrieval was unsuccessful, items encoded in emotional contexts elicited enhanced activity in right amygdala and a right-lateralized network that included extrastriate visual areas. These findings indicate distinct effects of emotion on successful and unsuccessful retrieval of source information, including lateralization of amygdala responses.

Adolescent↗