CORTICAL RESPONSE TO ACTIVITY OF CALLOSAL NEURONS

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Abstract
Neurous contributing axons or collaterals to the corpus callosum are mainly situated in the deeper strata of the cerebral cortex, whereas the terminals of these fibers are mainly distributed as free nerve endings in layers I, II and III. This anatomical fact is considered to be the major factor determining the pattern of the cortical response to stimulation of a symmetrical point on the opposite hemisphere. The homotopical relationship between the 2 hemispheres has been confirmed. There also exists a topical relationship between the corpus callosum and the cortex. The pattern of callosal potential varies with the stimulus strength, and can be broken up into 3 partly superimposed constituent parts: The first is an initial positive phase caused by the antidromic volley and the presynaptic orthodromic impulses; the 2d is a superimposed sharp negative deflection which is interpreted as representing the activity of the superficially placed callosal afferents and their postsynaptic neurons; and the 3rd is a slightly prolonged positive-negative diphasic wave attributable to the activity of the rather diffused callosal afferents in the 2d and 3rd layers and the subsequent postsynaptic discharges. The 2d component can be readily abolished by topical appln. of novocaine on the cortical surface. Strychnine has little effect on the 1st and the 2d components.