Somatosensory and auditory evoked potential studies of functional differences between the cerebral hemispheres in psychosis.

Evidence of lateralized hemispheric dysfunction in schizophrenia was previously found with a measure of visual evoked potential (VEP) wave-shape stability. The purpose of this study was to determine whether the VEP findings would extend to the auditory and somatosensory modalities. Measures of wave-shape stability were computed for auditory (AEP) and somatosensory (SEP) evoked potentials, recorded from one EOG and 14 scalp leads. Subjects were 74 unmedicated patients (49 schizophrenics, 25 nonpsychotics) and 27 nonpatients; two sets of age- and sex-matched comparison groups were formed. Main findings were: (i) Overtly psychotic schizophrenics exhibited lower than normal stability in left hemisphere AEPs (15-100 msec poststimulus). (ii) Both overtly psychotic and latent schizophrenics showed lower than normal wave-form stability, bilaterally, in the later epoch of AEPs (101-450 msec poststimulus). (iii) A subgroup of overt schizophrenics (other than chronic paranoid or chronic undifferentiated) had lower than normal stability in SEPs (15-100 msec) evoked by right median nerve stimuli and recorded from the right (ipsilateral) hemisphere. It was concluded that only the AEP results augment the previous VEP evidence indicating left hemisphere involvement in schizophrenic dysfunction.