Synchronization and desynchronization in the thalamus of the unanaesthetized decorticate cat

Abstract

The cellular activity in various parts of the thalamus was recorded extracellularly with multiple electrodes in unanaesthetized decorticate cats. During the transition from desynchronized to synchronized activity spindles appeared first in the medial parts of the thalamus associated with a decrease in the background cellular discharge. In the ventro-basal thalamus the development of spindles was facilitated by a decrease in the background discharge rate of single cells. The presence of spindles in the medial thalamus appeared to be a prerequisite for spindling in the lateral thalamus during certain conditions and there was a definite time relation between the spindles in the medial and ventrobasal thalamus. During well developed spindles and a strongly reduced background activity in the medial thalamus, occurring spontaneously or after giving barbiturates, this time relation was weaker. Strong peripheral stimuli gave long lasting abolition of spindles, both in the medial and lateral parts of the thalamus and in the cortex. However, the activity in the dorsal parts of the thalamus was not altered significantly. Light stimuli such as brushing hair increased the irregular discharge rate of single cells and abolished spindles only in the region of the ventro-basal complex which receives a short latency projection from the stumulated area. It is suggested that generalized synchronization and desynchronization of the thalamic and cortical activity is primarily due to changes in the excitability of cells in the rhythm generating mechanism in the medial thalamic nuclei which act as a gating mechanism modifying the excitability of the rhythm generators in other parts of the thalamus via a balance between the activity in inhibitory and excitatory connexions.