The post-stimulus-time histograms of single unit responses recorded extracellularly from simple and complex cells in the paralyzed cat’s striate cortex were compared both with the averaged visual evoked potential (VEP) recorded with the same stainless steel microelectrode and with the averaged surface VEP recorded with a silver-ball electrode applied close to the locus of microelectrode penetration. Diffuse and patterned white light stimuli, projected on a tangent screen in front of the animal, were used monocularly and binocularly at an intensity range over 2.5 log units. The latencies of spike responses to contralateral stimuli were found on the average shorter than those to ipsilateral and generally equal to those following binocular stimulation. The reciprocals of latencies as function of log stimulus intensity of the surface VEPs had the same gradient as those from averaged unit responses. In recordings from any given cell, the spike discharges displayed a fixed phase relationship to the local and another to the surface VEP, but this was not necessarily identical in different cells. These discharges may be related to the negative and positive phases of both types of slow waves. The surface and local VEPs elicited by binocular diffuse light stimulation represent the algebraic summation of the VEPs produced by ipsi- and contralateral stimulations, which confirms and expands earlier studies. No algebraic summation was found in the spike response, the sum of the two monocular responses being in most cases larger than the binocular.
Latencies and correlation in single units and visual evoked potentials in the cat striate cortex following monocular and binocular stimulations
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