INTERACTION OF EVOKED CORTICAL POTENTIALS

Abstract

The interaction in the sensory cortex of the thalamic, callosal and topically induced cortical impulses has been studied by means of various combinations of paired stimuli delivered at different intervals. It has been found that the early positive phase of the caliosal potential and the topically evoked dendritic potential are mutually exclusive. The negative component of the callosal potential can be completely inhibited by the dendritic potential, and, similarly, the dendritic potential will be completely blocked if the direct cortical stimulation is made during the rising phase of the negative wave of the callosal response. The interaction between the thalamic and callosal volleys is characterized by the following phenomena: (1) The first negative component of the callosal potential has a blocking effect on the positive component of the primary cortical response to auditory (thalamic) stimulation. (2) The negative component of the cortical response to sound stimulation suffers severe and prolonged inhibition from the callosal potential. The former is believed to be due to the partial involvement of apical dendrites of common neurons in both kinds of potentials, and the latter can be taken as an indication of inhibitory effect from the activity of intracortical internuncial neurons.