Inhibition of primate spinothalamic tract neurons by stimulation in ventral posterior lateral (VPLc) thalamic nucleus: possible mechanisms

The inhibitory effects of stimulation in the caudal part of the ipsilateral or contralateral ventral posterior lateral (VPL sub(c)) thalamus nucleus were examined in recordings from 52 spinothalamic tract (STT) neurons in the lumbosacral enlargement of anesthetized monkeys. The stimulation site in the contralateral VPL sub(c) nucleus was also employed to activate STT cells antidromically and thus, when testing for inhibitory effects, the stimulus strength was kept below the antidromic activation threshold. STT neurons were classified as wide dynamic range (WDR) or high threshold (HT) on the basis of their responses to mechanical stimulation of their cutaneous receptive fields.