An analysis of spontaneous impulse activity of units in the striate cortex of unrestrained cats

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Abstract
Recordings were made from 65 cells in the visual cortex of unanaesthetized, dark-adapted cats and transferred automatically to computer input paper tape. The activity of each cell was measured as a function of time (the running mean). The unit of time used was inversely proportional to the mean firing rate, in order to give comparable results for different cells. For 69 sections of discharge from 52 cells, the length of time recorded was sufficient to test for the long-term stability of the running mean. In 26 sections, various kinds of trend and long-term irregularity were found. The interspike interval histogram was computed for the 41 sections (from 31 cells) in which there were more than 2000 discharges. Only 8 histograms approximated closely to the exponential form. A test was also made of the distribution of the longer intervals alone and and in 25 sections they did not deviate significantly from the exponential form. There was no significant correlation between the behavior of the longer interspike intervals and the long-term stability or otherwise of the running mean.