Spatial organization of interaction of transcallosal and thalamocortical flows of excitation

The interaction between transcallosal potentials and the responses to stimulation of the contralateral sciatic nerve was studied at 85 sites in the sensorimotor region of the cortex in acute experiments on cats. It was shown that the effect of the interaction of these responses is determined by their configuration at the given site, as well as by the time interval between responses. The interaction was of a pronounced spatial-temporal character. Facilitatory influences were localized, as a rule, in the zone of overlap of the foci of evoked potentials, while the peripheral areas of the cortex were in large degree subjected to the depressant action of the transcallosal flow. At the same time the regions between sites were characterized by a dynamic succession of facilitatory and depressant influences. The described interaction effects are viewed as a manifestation of the modulating function of the transcallosal flow, which realizes the concentration and contrasting of the excitation propagated along ascending pathways.