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Biomedical subjects

D W Zaidel

Publications and source records attributed to D W Zaidel.

31 records · Page 2Linked to original sources
PubMed1995

The case for a relationship between human memory, hippocampus and corpus callosum.

Unilateral brain damage which includes the hippocampus leads to memory impairments consistent with hemispheric specialization on the same side. Damage to the corpus callosum, the major connecting pathway between the left and right hemispheres, also leads to memory impairments. This suggests both hemispheric specialization on the hippocampal level and a critical role for the corpus callosum in memory functions. A complete hippocampal formation is present on either side of the brain but traditionally only one is studied. However, a comparison between the neuronal populations in the hippocampus on both sides revealed asymmetry in connectivity among hippocampal subfields. The profile of memory impairments of commissurotomy ('split-brain') patients is described. The results are discussed in terms of a relationship between hippocampus and corpus callosum in humans. As hemispheric specialization evolved, inter-hippocampal connections became less important and the corpus callosum became prominent in memory functions.

Corpus Callosum↗
PubMed1994

Sex-related asymmetries in the morphology of the left and right hippocampi? A follow-up study on epileptic patients.

Cell densities were determined in left and right surgically removed hippocampal tissue of epileptic patients. Pyramidal cells were studied in CA1, CA4, and the dentate gyrus. Lower densities of nucleolated cells were found for males in the right CA1 and CA4 than on the left while there was no significant left-right difference in females. Moreover, we found a probable sex difference in intercorrelations of nucleolated cells among the three subfields. In males, they were positive and significant on the left while they were low on the right. In females, positive significant intercorrelations were obtained between some subfields and not between other subfields, on either side. The present findings suggest greater hippocampal lateralization in males than in females with higher hippocampal neuronal connectivity on the left in males than on the right.

Adolescent↗
PubMed1994

Memory for faces in epileptic children before and after brain surgery.

Memory for pairs of unfamiliar children's faces was investigated in 29 children and adolescents suffering from left (LTLE) or right (RTLE) temporal-lobe epilepsy, before and after temporal-lobe surgery. Both immediate and delayed memory were tested. Before surgery, RTLE subjects performed worse than either LTLE subjects or normal children. After surgery, RTLE subjects improved significantly. Overall (after surgery), there was no significant LTLE-RTLE difference, but on delayed memory, the RTLE group was worse than the LTLE group. The results suggest specialization for facial memory in the right hemisphere of young patients, as in adults, despite early brain damage.

Adolescent↗
PubMed1993

Regional differentiation of cell densities in the left and right hippocampi of epileptic patients.

Neuronal cell densities in surgically removed left or right hippocampal tissue of epileptic patients suffering from temporal lobe epilepsy were determined in CA1, CA4, and the dentate gyrus (DG). Mean densities showed no statistically significant left-right asymmetry in CA1 and the DG, consistent with findings by others. Mean densities did show previously unreported asymmetry in CA4; densities were significantly lower in the right CA4 than in the left. Another new finding is an asymmetry in regional intercorrelations: positive and significant correlations among the three subfields were obtained only in the left hippocampus. In addition, we confirmed previous findings of positive correlation between neuronal densities in CA1 and age of onset of habitual epilepsy, on either side. Taken together, the results suggest subtle left-right asymmetries in the vulnerability of the hippocampi to epilepsy-associated damage and/or higher neuronal connectivity or interdependence on the left than on the right.

Adult↗
PubMed1990

Learning a unimanual motor skill by partial commissurotomy patients.

A series of motor tests on four Chinese partial commissurotomy patients is reported. The single-stage commissurotomy in all four patients included the anterior commissures and two-thirds or four-fifths section of the corpus callosum with sparing of the splenium. There was no demonstrable ability to transfer hand posture in these patients. This was the major evidence for functional deconnexion. A newly learned task of one-hand knotting revealed right hand impairment in all four patients. There was no dyspraxia in the right hand for over-learned object-handling tasks in these patients. It is suggested that there might be right hemisphere specialisation for the initial acquisition of unimanual object-handling skills and that the spared callosal fibres in the splenium alone are insufficient to mediate task control under these conditions. This is supported by the finding that one of these patients, who was the only one who had a right parietal lesion, was unable to perform the newly learned task with either hand.

Adolescent↗
PubMed1989

Hemispheric memory for surrealistic versus realistic paintings.

The issue of hemispheric processing of art works, either alone or in relation to a certain aspect of language, was investigated in normal subjects. Three experiments were performed. In the first, memory for surrealistic versus realistic pictures was investigated. In the second, memory for metaphoric versus literal titles of these pictures was measured. In the third, memory for the paintings was determined as a function of the same titles. The results of the first experiment showed a right visual field (RVF) advantage for the surrealistic pictures. No field difference emerged for the realistic pictures. The results of the second experiment indicated a RVF advantage in memory for metaphoric titles. Moreover, in the RVF, there was an advantage for titles from surrealistic-metaphoric pairs over all other pairings. Results of experiment three showed a RVF advantage in remembering pictures from surrealistic-metaphoric pairs and, in the left visual field (LVF) there was advantage for pictures with literal titles. Taken together, the results suggest left hemisphere advantage in processing meaningful, yet incongruous arrays, both pictorial and linguistic. The results are discussed in terms of hemispheric memory for art works, metaphors, and the relationship between the two in the brain.

Adult↗
PubMed1988

Hemi-field asymmetries in memory for incongruous scenes.

The purpose of the present study was to investigate hemispheric asymmetries of long-term semantic memory in normal subjects. A hemi-field reaction time (RT) and accuracy paradigm was used and the test stimuli consisted of pictures, with different semantic organization. Two separate experiments were conducted. In the first, memory for pictures depicting common scenes or incongruous scenes was measured. In the second, we compared memory for incoherent scenes and the same incongruous scenes. The results showed no difference between the visual half-fields in accuracy scores. However, in both experiments the RT results showed that incongruous scenes were recognized consistently faster in the right visual half-field than in the left half-field. In addition, in the first experiment there was no visual field difference for common scenes. In the second experiment, there was a left visual field advantage for unorganized scenes. The results were interpreted to reflect hemispheric asymmetry in long-term semantic memory, in general, and showing a left hemisphere specialization for uncommon, unusual aspects of otherwise regular percepts, in particular. Applying schemata theory to the results, we discussed the possibility that the left hemisphere uses/stores schemata conducive to "flexible" thinking strategies while the right hemisphere uses/stores schemata that involve "rigid" thinking strategies.

Adult↗
PubMed1987

Hemispheric asymmetry in memory for pictorial semantics in normal subjects.

Effects of presence versus absence of semantic organization in pictorial scenes were investigated in a memory hemi-field tachistoscopic paradigm in order to assess the hemispheric status of long-term semantic memory (LTSM). Forty normal subjects were asked to remember a series of pictorial scenes which were organized either in common configurations or were unorganized with respect to real-world configurations. Memory for these scenes was measured by hemi-field presentations of detail probes and whole scene probes. The results showed that there were no differences between the two visual fields in accuracy scores. Latency of positive responses showed that memory for the common/organized scenes was better in the left (LVF) than in the right visual field (RVF) and a dissociation between the two types of pictorial organization was present only in the LVF, with the slower latencies for unorganized scenes. The effect of probe-type was also different in the two visual fields: detail and whole scene probes were undifferentiated within the LVF but were differentiated in the RVF, with whole scenes remembered more quickly. The findings are discussed in terms of asymmetries in storage/retrieval of schemata in LTSM.

Female↗
PubMed1986

Memory for scenes in stroke patients. Hemisphere processing of semantic organization in pictures.

Twenty-one patients with cerebrovascular lesions in posterior regions of the left or right cerebral hemispheres and nonfluent aphasics with damage in anterior regions of the left hemisphere were administered a specially designed multiple-object pictorial test which measured long-term memory for scenes depicting real world schemata versus jumbled unorganized scenes. The units in the pictures were familiar figures. Memory was tested separately for single details and for whole scenes. The results showed that within the left posterior group there was significantly poorer memory for unorganized relative to organized stimuli, especially for whole scenes. There was also a selective dissociation between the left and right posterior patients on the detail versus whole scene probes in the unorganized stimuli. At the same time, organized scenes depicting real world schemata were not selectively impaired in any of the patient groups. Further, the overall memory scores on the Memory for Pictorial Scenes Test obtained by the aphasic patients were not significantly lower than those obtained by the control subjects, while scores of both posterior groups were lower than the control group. Taken together, the data suggest the following. Pictorial semantics, like linguistic semantics, are functions processed by the left posterior cortex. While the posterior region in the left hemisphere plays a special role in remembering visual situational schemata that are newly encountered, familiar visual situational schemata may be bilaterally represented.

Cerebral Cortex↗
PubMedDate not supplied

Brain and face: communicating signals of health in the left and right sides of the face.

In human communication and mate selection the appearance of health sends signals regarding biological fitness. We compared the appearance of health in the sides of the face to previous results on left-right facial asymmetry in the appearance of beauty (1). The stimuli were created by aligning the left and right sides of the face each with its own mirror image. Here, participants viewed 38 pairs of left-left and right-right faces and judged which member of the pair looked healthier. No significant interaction emerged between decision (health vs attractiveness) and face side. Rather, in women's faces right-right was significantly more healthy and attractive than left-left, while in men's faces there was no significant left-right difference. In biology and evolution, health and beauty are closely linked and the findings here confirm this relationship in human faces.

Brain↗
PubMedDate not supplied

Hemispheric effects of canonical views of category members with known typicality levels.

Is there a preferred hemispheric canonical view of a concept? We investigated this question in a natural superordinate category membership decision task using a hemifield paradigm. Participants had to decide whether or not an image of an object lateralized in the left (LVF) or right (RVF) visual half-field is a member of a predesignated superordinate category. The objects represented high, medium, or low typicality levels, and each object had six different perspective views (front, front-right, front-left, side, back-left, and back-right). The latency responses revealed a significant interaction of Hemi Field X View X Typicality (there wasno hemifield difference in accuracy). The findings confirm the presence of asymmetry in stored concepts in long-term memory and suggest, in addition, a hemispheric canonical view of these concepts, a view strongly related to typicality level.

Adult↗