A new look at the human split brain.
The 'split-brain' syndrome results from the severance of neocortical commissures, and it is characterized by an incapacity of the cerebral hemispheres to exchange information and by the coexistence of two independent cognitive systems in the same cranium. Research on commissurotomized patients, for the most part, has focused on the disconnection and has treated the hemispheres as two independent entities. A different perspective was adopted in the present study, which considered the 'split brain' as a single organism, and the two disconnected hemispheres as integral components of this organism connected to one another through subcortical structures. Eight independent tasks were conducted on 2 commissurotomized patients who were presented tachistoscopically with simultaneous bilateral information such that neither hemisphere received sufficient information to make a final decision. Only by combining the initially segregated information could a correct response be produced. Both patients performed significantly above chance in 7 of the tasks (spatial orientation, calculation, lexical decision), suggesting that the information divided between the hemispheres could be united, related, and acted upon in a unified manner. This performance was achieved in spite of each hemisphere being unaware of the information received by the other, as typically observed in 'split-brain' patients. The results indicate the coexistence of perceptual disunity and behavioural unity, and they suggest that, even when the two disconnected hemispheres receive different information, the commissurotomized brain works as a single and unified organism.
Sergent
J
J
Montreal Neurological Institute, Quebec, Canada.
D000328:Adult; D001696:Biomechanical Phenomena; D001921:Brain / Q000601:surgery; D001927:Brain Diseases / Q000209:etiology / Q000503:physiopathology*; D002540:Cerebral Cortex / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D011183:Postoperative Complications; D014794:Visual Fields