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

Abstract

1. Recordings were made from sixty‐five cells in the visual cortex of unanaesthetized, dark‐adapted cats and transferred automatically to computer input paper tape. 2. 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. 3. For sixty‐nine sections of discharge from fifty‐two cells, the length of time recorded was sufficient to test for the long‐term stability of the running mean. In twenty‐six sections, various kinds of trend and long‐term irregularity were found. 4. The interspike interval histogram was computed for the forty‐one sections (from thirty‐one cells) in which there were more than 2000 discharges. Only eight histograms approximated closely to the exponential form. A test was also made of the distribution of the longer intervals alone and in twenty‐five sections they did not deviate significantly from the exponential form. 5. There was no significant correlation between the behaviour of the longer interspike intervals and the long‐term stability or otherwise of the running mean. © 1966 The Physiological Society