Functional Tests of the Corpus Callosum in Schizophrenia

DEARSat, Jones and Miller (Journal, December 1981, 139, 553â€”57) suggest that schizophrenia is a split-brain condition akin to agenesisof the corpus callosum. They have demonstrated that unlike normal subjects, patients with acute schizophrenia show simultaneous cortical evoked responsesto vibratory stimuli applied to eachindex finger. A more obvious conclusion from their work is that thesepatients simply have ipsilateral pathways to the CNS of near equal importance to the contralateral pathways. In normals most stimuli going to the CNS are projected preferentially to the contra lateral hemisphere,and activity in the corresponding part of the ipsilateral hemisphere is suppressed (Gazzaniga, 1974). Exceptions to this of course arise (e.g. visual stimuli are projected to both right and left cerebralhemisphereswithout suppression). A number of studies have tried to demonstrate a causative role in schizophrenia of damage to the corpus callosum. Most of these use as their starting point the study on only 10 chronic schizophrenic patients by Rosenthal and Bigelow, 1972.This study had a number of flaws including a low number of patients and the fact that a number of the controls suffered with alcoholism and 6 had a diagnosis of personality disorder (no criteria given). Even if the corpus callosum is thickened in chronic schizophrenia, this does not mean that this is the primary disorder but might well be secondaryto either drug therapy or attempts by the body to compensate for damage of one hemisphere. A major flaw with the study by Beaumont and Dimond (1973)wasthat, in testing their subject for transfer of information across the corpus callosum, they relied on verbal replies and therefore their results could be interpreted as showing either problems in the corpus callosum or in the dominant hemisphereofschizophrenic patients. The evidence from Green's (1978) work would on first sight appear to be contradictory to the results obtained by Jonesand Miller, for surely if information from one hand is relayed equally to both cerebral hemispheres,then interhemispheric transfer would not benecessaryfor the other hand to perform a task. A number of authors (Gruzelier and Venables, 1974; Our, 1977; Taylor, Greenspan and Abrams, 1979; Schweitzer, Baker and Welsh, 1978; Flor Henry, 1969)have hinted that in schizophrenia, there might well be a lesion of the dominant hemisphere but so far, neither the investigation of the corpus callosum nor the investigation of the left cerebral hemispherehave thrown much light on the aetiology or treatment of the schizophrenias. However, the work of Jones and Miller opens a new avenueto the investigation of schizophrenia.The underlying anatomical problems in schizophreniamay be in the presenceof unduly large ipsilateral pathways to and from the cerebral hemispheres.These would result secondarily in failure of one hemisphere to suppress function in the other as normally occurs (Gazzaniga, 1974). IndeedGreen(1979)reported that by useof earplugs to occlude stimuli from one ear in schizophrenic patients, they obtained signifIcantly increased levels speech comprehension compared with everyday binaural hearing and perhaps a decreasein auditory hallucinations. By doing this they were clearly giving one hemisphereon advantagein dealing with auditory stimuli over the other, and thus facilitating that hemispherein suppressingthe oppositehemisphere. It might well be that the genetic predisposition in schizophrenia may be the presenceof an excessof ipsilateral sensory and motor tracts and indeed previous research has shown the presenceof major ipsilateral nervetracts in man (Levy, 1976). This study by Jonesand Miller certainly fits in with the theories of attention and perception describedby McGhie and Chapman (1961) and with the findings of a disorder of the arousal mechanism (Claridge, 1972). It is also easyto seehow the dopamine hypo thesiswould fit in with this scheme.