[Influence of lesion of motor cortex on second somatosensory area emanating descending modulation on thalamic...

The present study was undertaken to verify further the participation of motor cortex (MCtx) in the somatosensory area II(SII) emanating descending modulation of thalamic intralaminar nuclei (ILN). Neuronal responses in ILN to noxious stimulation of the superficial peroneal nerve were extracellularly recorded in 34 cats. The effects of electrical stimulating SII on nociceptive responses of neurons in ILN before and after lesion of MCtx were observed and compared. It was shown that electrical stimulation of SII obviously inhibited the nociceptive responses in the majority of neurons recorded (11/13) in ILN in the cats with MCtx intact (P < 0.05). After lesion of MCtx the inhibitory effect still remained (n = 10, P < 0.05), but weakened to a certain extent compared with that before lesion. In the animals with the lesion involving MCtx and the underlying subcortical structures electrical stimulating SII facilitated the nociceptive responses of ILN neurons (n = 7, P < 0.05). The results further support the idea that SII emanating descending modulation on ILN is in part fulfilled via MCtx.