Intracellular Recording of the Convergence of Input upon Neurons in Cat Association Cortex

Intracellular responses in anterior middle suprasylvian gyrus to peripheral stimuli (light flash, auditory click, and contralateral forepaw shock) and central stimuli (contralateral cortical and tha!amic stimulation) were studied in cats anesthetized with chloralose. When cells discharged to peripheral and some central stimuli, spikes arose from asynchronous, summating, depolarizing postsynaptic potentials of 20- to 80-msec duration. Long-duration (30-300 msec) hyperpolarizing poten-tials also were evoked by one or more peripheral and central stimuli in over one-third of cells studied, and represent inhibitory activity at the recorded cell or at previous central synapses. In many instances, cortical inhibitory mechanisms were responsible for blocking effects during interactions between pairs of stimuli. How-ever, when light flash was the conditioning stimulus, the block usually occurred before the recorded cell, either in cortex, or possibly in precortical areas of neuronal convergence. The data indicate that this portion of suprasylvian gyrus in the cat is unequally responsive to various stimuli, with different synaptic patterns of activity evoked by photic and other peripheral and central inputs