Neuronal discharges of the ventrolateral nucleus of the thalamus during sleep and wakefulness in the cat II. Evoked activity

Summary

Neuronal discharges were recorded with extracellular microelectrodes in the ventrolateral nucleus (VL) of the thalamus in cats immobilized with gallamine. These animals had been previously implanted with a plastic cylinder under general anaesthesia a few days before chronic recording. The units recorded responded monosynaptically to brachium conjunctivum (BC) stimulation and were at times identified as true thalamo-cortical relay cells by antidromic activation from motor cortex stimulation. The responses obtained from these neurons to single shock stimuli applied to BC were examined during spontaneous episodes of waking (W), slow wave sleep (SWS) and fast wave sleep (FWS).

During W the response consits of a single monosynaptic spike followed by a period of silence lasting from 40–80 msec. During SWS, the response becomes unpredictable. It can consist of a single spike as in W or, more frequently, there is either no response at all or a firing of the cell in a high frequency burst occuring at variable latencies and the silent period is longer (60–200 msec) than in W. During FWS, the response is identical as that observed in W but the silent period that follows is of intermediate duration between W and SWS.

Neurons in the nucleus reticularis thalami respond to BC stimulation during W with a firing pattern that appears as the converse of that of VL neurons.