Driving of slow oscillations in the somatosensory system of the cat

Abstract

Evoked potentials and neuronal activity, induced by repetitive stimulation of the sciatic nerve with brief electrical pulses, were recorded simultaneously from the surface and depth of the cerebral cortex and the specific and non-specific nublei of the thalamus, in cats under gallamine as well as in cats under barbiturates. Averaging and spectral analysis showed that the evoked potentials contained time locked components ranging in frequency from 0.5–6 c/sec and extending over periods as long as 3500 msec after the stimulus. When the frequency of stimulation was progressively increased from 0.25–6 pulses/sec it was found that the late oscillations could be “driven” at specific frequencies which caused an increase in the amplitudes of specific frequency components, harmonically related to each other and to the frequency of stimulation. The administration of barbiturates caused changes in the specific frequencies at which the late oscillations could be driven most effectively. These results are analogous to those obtained in the analysis of the late oscillations evoked in the human EEG by stimulation of the median nerve. Post stimulus histogram computed from the neuronal activity associated with the evoked potentials show that the peaks which indicate high levels of neuronal discharge, occur at intervals closely related to the period of the late oscillations. The time and phase relations between the late oscillations recorded from the cortex, the specific and the non specific thalamus, the time and phase relations between the discharge of different groups of neurons associated with them, and the fact that they can all be driven simultaneously at specific frequencies of stimulation, suggest that these phenomena are related to the driving, at resonant frequencies, of activities which develop in thalamic, cortical and thalamocortical feedback loops.