Abstract
Extracellular records were made of single intralaminar thalamic unit activity evoked by electrical stimulation of the fastigial nucleus and the radial nerve in 38 cats anaesthetized with α-hloralose. Effects of conditioning cortical shocks on those responses and pharmacological properties of the cortical influences were studied. Among a total of 294 intralaminar units recorded, 248 units (84%) were activated by stimulation of each of the bilateral radial nerves in a convergent manner at latencies ranging from 5 to 45 msec (mean latency, 21.5msec). All of these 248 intralaminar neurones were also driven by stimulation of the fastigial nucleus at latencies ranging from 5 to 35 msec (mean latency, 12.9 msec) and they followed repetitive fastigial stimulation up to 20 Hz. Ninety-one per cent of intralaminar unitary responses evoked by both peripheral and fastigial stimulation were inhibited following conditioning stimulation applied on the anterior sigmoid gyrus. The inhibitory influence of the cerebral cortex on intralaminar neurones was completely blocked by strychnine (0.2–0.4 mg/kg) and was not blocked by picrotoxin (2–4 mg/kg) administered intravenously. The mechanism of cortical inhibitory influences and the possibility of the existence of inhibitory interneurones in the thalamus are discussed.
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