Biomedical subjects

Kylie J Barnett

Publications and source records attributed to Kylie J Barnett.

9 recordsLinked to original sources

PubMed2006

Bilateral disadvantage: lack of interhemispheric cooperation in schizophrenia.

Language anomalies and left-hemisphere dysfunction are commonly reported in schizophrenia. Additional evidence also suggests differences in the integration of information between the hemispheres. Bilateral gain is the increase in accuracy and decrease in latency that occurs when identical information is presented simultaneously to both hemispheres. This study measured bilateral gain in controls (n=20) and individuals with schizophrenia (n=10) using a lexical-decision task where word or non-word judgements were made to letter strings presented in the left visual field (LVF), right visual field (RVF) or bilaterally (BVF). Language was not abnormally lateralized in the schizophrenia group. Controls exhibited the expected decrease in latency when words were presented bilaterally. This effect was not observed in the schizophrenia group who were actually disadvantaged in this condition. The lack of bilateral gain in schizophrenia is discussed as arising from differences in the connections between areas in each hemisphere that mediate language.

Adult↗

PubMed2006

Schizophrenia and rightward bias in line bisection.

This study investigated line bisection in 10 males with schizophrenia and 15 controls. There was an overall leftward bias, consistent with slight right "pseudoneglect", but the schizophrenia group showed more variation with experimental conditions, suggesting impaired interhemispheric transfer. Specifically, the rightward bias was especially marked when the lines were positioned on the right side of the page, when the right hand was used, and when a right to left scan was adopted. The rightward bias was associated with the predominance of negative symptoms. Findings are discussed with reference to the role of the corpus callosum in the transfer of spatial attention.

Adult↗

PubMed2005

Symmetry of callosal information transfer in schizophrenia: a preliminary study.

OBJECTIVE: While there is much evidence to suggest left hemisphere dysfunction and interhemispheric transfer deficits in schizophrenia, the right hemisphere is rarely implicated. This study uses 128-channel EEG to assess whether asymmetry of interhemispheric transfer found in normal individuals is present in those with schizophrenia, and whether this might point to a right-hemisphere dysfunction. METHODS: Simple reaction time (RT) was recorded to stimuli presented to the left visual field (LVF), right visual field (RVF) or bilaterally (BVF) in 13 males with schizophrenia and 13 controls. 128-Channel EEG was simultaneously recorded. Interhemispheric transfer time (IHTT) in each direction was calculated by comparing the latencies of N160 EP components in the hemispheres contralateral and ipsilateral to stimulation. RESULTS: While controls showed faster information transfer from the right-to-left hemisphere, this asymmetry was not present in the schizophrenia group who also exhibited a concomitant decrease in the amplitude of the N160 in the right hemisphere. CONCLUSIONS: Results are interpreted with reference to a loss of rapidly conducting myelinated axons in the right hemisphere in schizophrenia.

Adult↗

PubMed2005

Lack of asymmetrical transfer for linguistic stimuli in schizophrenia: an ERP study.

OBJECTIVE: To assess the mechanisms underlying lack of speeded information transfer asymmetry (faster right to left) for verbal information in schizophrenia. METHODS: Interhemispheric transfer times (IHTT) between the hemispheres were assessed using a lateralized lexical-decision task in males with schizophrenia (N = 12) and matched controls (N = 12). Words were presented to the left visual field (LVF), right visual field (RVF), or bilaterally (BVF) while 128-channel EEG was recorded continuously. A direct measure of IHTT in each direction was obtained by comparing the latencies of the N160 evoked potential (EP) component in the hemispheres contralateral and ipsilateral to stimulation. RESULTS: Controls showed faster information transfer from the right to left hemisphere (R-to-L) for linguistic stimuli. The two groups did not differ for IHTTs L-to-R. Lack of IHTT asymmetry in the schizophrenia groups was associated with an overall concomitant decrease in the amplitude of the N160 in the right hemisphere. CONCLUSIONS: Differences in IHTT asymmetry may be attributed to lack of right hemisphere activation and not callosal dysfunction as has been previously suggested. SIGNIFICANCE: It is suggested that a relative excess of myelinated axons in the right hemisphere speeds IHTT faster R-to-L, findings are discussed with reference to differences in right hemisphere white matter connectivity in schizophrenia.

Adult↗

PubMed2005

Right hemispheric dysfunction in schizophrenia.

This study uses the Poffenberger (1912) paradigm, which compares the difference between "crossed" (stimuli and motor response areas are contralateral) and "uncrossed" (stimuli and motor response areas are ipsilateral) conditions to estimate interhemispheric transfer time. Simple reaction time (RT) was recorded to stimuli presented to the left visual field (LVF), right visual field (RVF), or bilaterally (BVF) in individuals with schizophrenia (n = 10) and controls (n = 14), who responded using either the left or right hand. While the results provide no evidence for differences between the groups in information transfer between the hemispheres, the schizophrenia group were significantly slower to respond to LVF stimuli, suggesting right hemisphere dysfunction.

Brain↗

PubMed2004

Hemispheric integration and differences in perception of a line-motion illusion in the divided brain.

Five people lacking the corpus callosum (two callosotomized, three with agenesis of the corpus callosum) and neurologically normal subjects were shown vertical lines that appeared instantaneously between pairs of rectangles in one or other visual field. When one of the rectangles flashed prior to the presentation of the line, and the line was in the same visual field, all subjects perceived the line as spreading from the flashed rectangle to the other. Normal subjects and one of the callosotomized subjects showed a slight but significant right visual-field advantage, perhaps reflecting a left-hemispheric superiority in processing rapid temporal events. The illusion was also induced when the line and the flash were in opposite visual fields in one of the callosotomized, one of the acallosal subjects, and about half of the normal subjects, implying interhemispheric integration even in the absence of the corpus callosum.

Adult↗

PubMed2002

Paradoxical interhemispheric summation in the split brain.

We measured simple reaction time (RT) to light flashes, presented either singly or in pairs, in two people who had undergone callosotomy, one person with agenesis of the corpus callosum, and 17 normal subjects. The three split-brained subjects' RTs were decreased to bilateral pairs beyond predictions based on a simple race between independent unilateral processes, while those of the normal subjects were actually longer than predicted by the race model. This effect was present whether the bilateral pairs were in mirror-image locations or not, but was not present when the pairs were presented unilaterally. Since summation does not depend on close spatial correspondence, and also occurs when inputs are staggered in time, we suggest that it is due to cortical projection to a subcortical arousal system, and is normally inhibited by the corpus callosum.

Adult↗

PubMed2002

Ambidexterity and magical ideation.

In a sample of 250 healthy undergraduate students, scores on a scale of magical ideation rose to a peak at the point of ambilaterality on a scale of hand preference, and fell away with increasing right- or left-handedness. This effect mirrors that reported by Crow, Crow, Done, and Leask (1998) who found a dip in academic abilities at the point of ambilaterality, or what they call ''the point of hemispheric indecision''. We relate these findings to genetic theories of laterality in which one allele (RS+) codes for left-cerebral dominance while the other (RS-) leaves laterality to chance. RS-- homozygotes may be susceptible to a lack of dominance, resulting in a disposition to magical ideation and an increased risk of schizophrenia, but also enhanced creativity and lateral thinking.

Journal Article↗

PubMedDate not supplied

Speeded right-to-left information transfer: the result of speeded transmission in right-hemisphere axons?

Both reaction time (RT) and evoked potential (EP) studies have shown that interhemispheric transfer is faster from the right to the left hemisphere than vice versa. This has been explained either in terms of an asymmetry of callosal fibres or as a result of hemispheric specialization. Here we suggest that it may be due to greater activity resulting from a greater number of fast-conducting, myelinated fibres in the right hemisphere than in the left. Interhemispheric transfer times (IHTTs) were measured in 13 males by comparing latencies and amplitudes of N160 EPs ipsilateral and contralateral to checkerboard stimuli presented to the left or right visual field. IHTT estimates were obtained from three homologous electrode pairs. The shorter IHTT from right-to-left was associated with a concomitant increase in N160 negativity in the right hemisphere. There was no evidence from RTs to stimuli in each visual field to suggest that the right hemisphere was dominant for this task, suggesting that the faster speed of transfer from the right-to-left hemisphere may depend on faster axonal conduction in the right hemisphere relative to the left.

Adult↗