Biomedical subjects

Michael Hornberger

Publications and source records attributed to Michael Hornberger.

5 recordsLinked to original sources

PubMed2006

Abnormal categorization and perceptual learning in patients with hippocampal damage.

Prevailing theory holds that the medial temporal lobe (MTL) subserves declarative memory exclusively, whereas nondeclarative memory is independent of this brain region. Recent studies in patients with amnesia, however, have shown that performance on declarative memory tasks may not always be dependent on a single MTL memory system, instead highlighting the critical role of anatomically distinct structures in processing different stimulus types. In particular, the hippocampus has been implicated in spatial memory, whereas perirhinal cortex seems critical for object memory. To assess whether stimulus type would also be a key dimension in nondeclarative memory, patients with selective hippocampal lesions were tested on simple categorization and perceptual learning of faces and virtual reality scenes. The patients demonstrated preserved categorization and perceptual learning of faces but abnormal performance when the stimuli to be discriminated were virtual reality scenes. These findings imply that stimulus type may be a more critical predictor of performance on memory tasks (declarative and nondeclarative) than previously thought. They also suggest that reports of good nondeclarative memory after MTL damage may, in some cases, simply reflect the use of stimuli that fail to tap the processes dependent on structures in this region, such as spatial processing in the case of the hippocampus.

Adult↗

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

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↗

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

Neural correlates of retrieval orientation: effects of study-test similarity.

ERPs elicited by correctly classified unstudied items in tests of yes/no recognition memory were used to investigate the neural correlates of retrieval cue processing. Items in Experiment 1 consisted of pictures and their corresponding names, allowing study and test material to be factorially crossed in four separate study-test cycles. The ERPs elicited by unstudied pictures and words were, in each case, more negative-going when the study material belonged to the alternative rather than the same class of items. These findings demonstrate that previously reported ERP "retrieval orientation effects" depend on differences in similarity between study and test items, and not on the form of the sought for material. In Experiments 2a and 2b, study materials were auditory words and pictures, and the test items were visual words. In both experiments, ERPs elicited by unstudied test words were more negative-going when pictures rather than auditory words were the study material. Thus, ERP retrieval orientation effects do not depend on the employment of a copy cue condition. It is proposed that the effects reflect differences in the processing necessary to maximize overlap between cue and memory representations.

Acoustic Stimulation↗