Multicellular discharges in the somatosensory cortex of cats at rest and during spontaneous EEG activation

Abstract

Multicellular activity and the EEG were recorded from the somatosensory cortex by means of metal microelectrodes 30 µ in diameter in chronic experiments on waking unrestrained cats. Unit activity was separated into three different amplitudes by means of a discriminator. Three types of spontaneous activity were distinguished: with continuous, burst, and grouped discharges. Despite the outwardly identical picture of the spontaneous EEG activation reaction, parallel processes, differing in sign and distribution of unit activity were discovered in the neuron population. Their combinations were very varied. This activity could increase in frequency at all amplitude levels or at only one or two levels, accompanied by inhibition of discharges (or by no change) at other levels. The character of reorganization was shown to depend largely on the degree of the spontaneous EEG activation reaction and on the type of spontaneous unit activity. Computer analysis of the changes in the mean discharge frequency showed that during EEG activation stimulation of unit activity (55%) predominated over depression (21%). In some cell populations the sequence of discharges was altered without any change in mean frequency. The experimental results are discussed from the standpoint of the role of unit activity in spontaneous EEG activation.