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.