Tactile-evoked potentials in schizophrenia. Interhemispheric transfer and drug effects

EEG potentials evoked by tactile stimulation of the forearm (tactile-evoked potentials or TEPs) were recorded simultaneously from both cerebral hemispheres in a group of schizophrenics and a group of healthy control subjects. Differences between the groups were found for the early waves of the TEPs: in the control subjects the first two positive waves (P25 and P50) and the first negative wave (N35) recorded from the hemisphere on the same side as the stimulation were slower (i.e. had longer latency) than those recorded from the hemisphere contralateral to the stimulation. This 'lateralization effect' was not seen in the schizophrenic subjects. It was concluded that the TEPs recorded from the hemisphere ipsilateral to the stimulus were not being transmitted from the other hemisphere via the corpus callosum and must therefore have been transmitted via direct ipsilateral pathways from the periphery. In a second experiment the drug pindolol was administered to schizophrenic subjects but differences in P50 latency between ipsilateral and contralateral hemispheres were found equally in both drug and placebo groups. We also found slight evidence to suggest that the more severely ill the patient the more similar the TEP latencies recorded from the contralateral and the ipsilateral hemispheres.