TIME SERIES ANALYSIS OF IMPULSE SEQUENCES OF THALAMIC SOMATIC SENSORY NEURONS

Abstract

Certain stochastic properties of sequences of impulses recorded from single thalamic lemniscal neurons were investigated in the de-afferented head, unanesthetized monkey. The results indicate that, in these sequences, neural impulses do not occur at random intervals. The deviation from randomness appears to be periodic in nature. There exist cyclic variations in the probability of occurrence of an impulse along the time continuum of neural activity and this periodic pattern extends usually for a few hundred milliseconds after the occurrence of any impulse in the sequence. During spontaneous activity the frequency of these periodicities is about 20-30 cycles/second and is unrelated to the mean frequency of the impulses in the sequence. The physiological factors related to these periodic variations are not known. The hypothesis is set forth that there are fluctuations in the effectiveness of the synaptic influences acting upon any single cell and that these fluctuations may depend upon the nature of the neural network of which the cell is a member.