Slow and spike components of the direct cortical response in the cerebral cortex.

Abstract

The direct cortical response (DCR) recorded from the motor cortex has been studied in rabbits. The results should be interpreted as suggesting that the called dendritic potential can be analysed into its component potentials: spike component with a steep rising phase and high amplitude; and slow component (SP) with a slower rise, more variable time course and low amplitude.1. In experiments of various stimulus strengths the SP occurs generally at weak stimulus, while the high amplitude response appears at strong one. As soon as the response exceeds about 0.5 mV which is usually the maximal value of SP, spike begins to appear, which finally reaches its maximal value with increase in the stimulus intensity.2. The spike component produced by maximal stimulation holds an absolute refractory period of about 3 msec. This indicates the spike component is an action potential of the responding neurones, presumably of the apical dendrites. On the other hand, SP which can summate without refractoriness shows a behavior of the graded response or postsynaptic potential. No satisfactory evidence has been found to identify the structure responsible for SP.3. Deterioration of the cortex prevents the spike from its ample development even by a maximal stimulation. In such a case an incomplete summation can be observed which, however, is considered to be a complete summation of the SP component in the response.4. From the distance-amplitude relation, the larger is the reduction rate (A1-A2/A1·100) the more the spike component is contained in the response, while theresponse showing smaller reduction rate has larger SP component regardless of the absolute amplitude.5. Superposition of SP on the spike component and vice versa can be recorded, suggesting that there is no mutual dependence between both components.This work was begun at the Physiological Laboratory, Research Institute of the Applied Electricity, Hokkaido University. The authors take this opportunity of thanking Prof. H. YOSHIMURA for his laboratory facilities to promote this work and acknowledge the cooperation of Drs. T. IKEDA, T. MIZOBUCHI, M. URUHA and H. KITASATO.