[Multineuronal characteristics of brain activation during extinction of the effects of indifferent stimuli].

In chronic experiments on cats, the correlation of multineuronal activity (MNA) in the somatosensory cortex with EEG activation reactions recorded at the same point was studied during the process of extinction. The MNA was discriminated in three amplitude levels and averaged by means of a computer. Three kinds of stimuli were used: electric shocks to the forepaw, sounds and direct stimulation of the midbrain reticular formation. It was found that with repetition of stimuli, the progressive inhibition of the EEG activation correlates with gradual reduction of the level of sharp increase of MNA frequency in response to stimulation, and with shortening of the poststimuli periods of prolonged frequency reduction. A minor part of neuronal populations reacted with a slowing down of the discharge frequency (e. g. to the sound and reticular stimulation). More specific frequency reactions during extinction were recorded at different amplitude levels, depending on the modality and the parameters of the stimuli and on the population type. The changes in multineuronal discharges rate were more diverse and more continuous than the EEG responses. A comparative study of both phenomena reveals only partial coherence between them.