The Functions of the Intercortical Neurones in Sensorimotor Coordination and Thinking in Man

Abstract

The manner in which the association pathways of the human brain integrate the effects of stimulation to cause verbal and motor response was studied in individuals in whom the intercortical pathways were sectioned to control convulsions. Response times of 3 reactions were measured before and after section of the nerve bands which connect the cerebral cortices: (1) simple reaction to visual, auditory, and tactile stimuli; (2) visual discrimination reactions; (3) verbal reactions in free-word association, op-posites association, and part-whole association. Reaction time equipment consisted of timing devices, manually operated keys, voice keys, and electrical circuits. The responses of 6 individuals were measured pre- and postoperatively after cutting the intercortical fibers. The results show that the cortical association neurones connecting the 2 hemispheres are important in determining direct responses to visual, auditory, and tactile stimuli. This role is one of dynamic regulation rather than discrete participation in the essential nerve channels of the responses. Crossed sensorimotor reactions and verbal associations were not significantly affected by section of the commissural neurones and it is believed that the associative mechanism acts in terms of generalized patterns of excitation which must include the sub-cortical centers. A defect in simple response times was the only well-established disturbance resulting from destruction of the commissural pathways and may explain the persistence of inertia in patients with such surgical lesions.