SEQUENCE OF EVENTS IN OPTIC CORTEX RESPONSE TO VOLLEYS OF IMPULSES IN THE RADIATION

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Abstract
In the response of the cat striate cortex under light anaesthesia following single shocks to the optic nerve a series of major spikes signalizes suscessive responses of cell bodies and their axons, as distinguished from longer-lasting waves assignable to dendritic activity. The intervals between such spikes are 1.4 msec. In geniculate and similar nuclei the synapse times is 0.6-0.7 msec, or half the above. The spike sequence has previously been found to represent discharges of successive cell groups situated at successively shallower levels of cortex. Employing a differential needle pair of recording electrodes, the point of one a fraction of a mm. above that of the other, minor spikes can be recorded between those of the major series. If it be inferred that an alternate sequence of major and minor spikes occurs, since conduction distances within the cortex are insignificant, the synapse times become 0.7 msec. The cortical neurons whose structure and spatial relationships are consistent with such an alternate series are pyramidal cells and short-axon cells. The lower amplitude of minor spikes is consistent with the random orientation of short-axon cells. From the records it is concluded that the afferent radiation fires short-axon cells, which in turn fire the 1st group of pyramids. These fire other short-axon cells via recurrent collaterals of their axons, etc. Certain speculations are appended as to possible elaboration of such a sequential activity in response to normal barrage stimulation by light to the retina, as compared to results of optic nerve stimulation by single shocks.