Brain disconnection, schizophrenia, and paranoia.

A lateral deficit explanation of schizophrenic cognition maintains that a left hemisphere deficit is characteristic of nonparanoid schizophrenia whereas right hemispheric deficits may be common in paranoid schizophrenia. An alternate explanation postulates an interhemispheric deficit in schizophrenic functioning. A major piece of evidence for this position is Beaumont and Dimond's oft-cited experiment matching pairs of stimuli presented to left, right, and both hemispheres (Beaumont, J. G., and Dimond, S. J. Brain disconnection and schizophrenia. Br. J. Psychiatry, 123: 661-662, 1973). We expanded upon this study and found left hemisphere deficits and interhemisphere deficits in schizophrenics. However, the type of deficit seemed directly related to the distinction of a paranoid-nonparanoid schizophrenic diagnosis. Paranoids match stimuli in all hemisphere conditions as well as control groups. Nonparanoid schizophrenics, on the other hand, had their greatest problem on all stimuli in the left hemisphere. Their right hemisphere performance was not different from other groups. The nonparanoid also exhibited problems in interhemispheric matching, but this seemed due to an impaired left hemisphere. Results, therefore, did not support an interhemisphere transfer deficit. A discussion of prior work suggests that the nonparanoid schizophrenic has a problem in serial processing in the left hemisphere.