UNITARY STUDY ON EVOKED ACTIVITY OF CALLOSAL NEURONS AND ITS EFFECT ON PYRAMIDAL TRACT CELL ACTIVITY ON CATS

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Microelectrode experiments were made on two kinds of cortical cells in the cat, each identified by antidromic stimulation. First, recordings were made from callosal neurons, and these were studied by radial nerve stimulation. Second, recordings were made from pyramidal tract cells (P. T. cells), and the effects of corpus callosum stimulation on the activities of P. T. cells were studied. All studies were carried out in the pericruciate cortex. The following results were obtained;
1) Out of 20 cells identified as callosal neurons, 12 were fired by single stimuli delivered to the superficial radial nerve. The latency of the discharge ranged from 12 to 20msec.
2) Single stimuli to the corpus callosum produced long lasting inhibitory effects on P. T. cells. The inhibitory effect seemed to start with a latency of 20 to 30msec. Though with most cells the effect was purely inhibitory (table 1), on rare occasions a transitory excitation preceded the inhibition.
3) In a few successful intracellular recordings from P. T. cells, a marked hyperpolarization of the membrane was observed to occur when firing was inhibited.