Some Effects of Cerebral Commissurotomy on Monkey and Man

Citation

Gazzaniga, Michael Saunders (1965) Some Effects of Cerebral Commissurotomy on Monkey and Man. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/BWV2-WE04. https://resolver.caltech.edu/CaltechETD:etd-02062003-152539

Abstract

The following studies were aimed at further clarification of certain of the functional effects produced by brain bisection in primates. They involved also the application and implications of brain bisection for problems of normal cerebral organization. In particular, extensive functional testing was carried out on two human patients in whom brain bisection had been performed for the treatment of severe epileptic seizures. In addition, these human studies were combined with experiments on certain related functions in monkeys. In the human experiments a variety of tests were administered which involved interhemispheric integration of sensory-sensory and sensory-motor information. The psychological capacities of each separated hemisphere were also examined. Results on somesthesis indicated predominately contralateral projection. Ipsilateral responses for some stimuli were apparent in one case suggesting direct afferent pathways may participate in a doubling of somesthetic representation of some body areas. Bilateral cortical projection for all types of somesthesis was indicated in results from the face and head. Visual testing revealed a complete gnostic separation of the left and right visual fields along with a complete lack of subcallosal interhemispheric interaction for any sort of visual stimuli. Motor control of both arms and both legs from one disconnected hemisphere varied but in general was possible in most testing situations. There was no interhemispheric transfer of learning and memory. Differences in intrinsic performance capacities of each separated hemisphere with regard to visual-constructional tasks and to speech and language functions were also observed. The left hemisphere appeared capable of verbal communication by both written and spoken means while the right, although unable to express itself in language of any form, could respond to certain verbal cues. Also, only the right hemisphere was capable of performing visual-constructional tasks. Related studies on monkeys concerning the neural mechanisms responsible for memory and visual-motor coordination, have revealed that pre-operatively learned visual discriminations are retained by only one hemisphere following brain bisection. In addition, control of the ipsilateral arm in split-brain monkeys was found to be impaired in visual learning situations but not in the habitual movements of everyday activity such as reaching for food.

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