Fibers from the cortical somatosensory area Ⅱ (SII) or motor cortex (MCtx) to intralaminar nuclei (ILN) have been proven to exist

and SII was found to be connected with MCtx by cortico-cortical fibers. The present work was undertaken to study whether MCtx participated in SII producing descending mdulation of ILN.All experiments were performed on sodium pentobarbitone anaesthetised cats. Single unit activities of ILN neurons were extracellularly recorded by glass microelectrodes. The effects of stimulating SII on nociceptive responses of ILN neurons were observed before and after cooling MCtx. The nociceptive responses of ILN neurons were attenuated by stimulating SII. There was a statistically significant difference at 0' - 2' after the stimulation (n= 14

P<0.05). The inhibitory effect of stimulating SII was reduced after cooIing MCtx (19℃ - 20℃) in 8 neurons

and abolished in other neurons when the temperature was below 18℃.MCtx was involved in SII producing descening modulation of ILN.