Inhibition of nociceptive discharges of parafascicular neurons by direct electrical stimulation of nucleus centrum medianum.

Pain evoked unit discharges in the parafascicular nucleus could be inhibited by direct electrical stimulation of the centromedian nucleus of thalamus, with residual inhibitory effect lasting for several minutes after cessation of stimulation. The optimal frequency of stimulation for production of the inhibitory effect was found to be 4--8 pulses per second. The duration of inhibition following each stimulating pulse lasted for 100--170 msec. Analysis of oscillographic records shows that there exists before the onset of the inhibition of parafascicular discharges a latent period of 10--20 msec which far exceeds the time required for impulse conduction between the two closely related structures, suggesting that a long tortuous neuronal circuit is involved in elaboration and transmission of the inhibitory effect.