| Abstract: | ![]()
Experimental evidence obtained from mi-croelectrode analysis of the nociceptive dis-charges of neuronsin themedicalthalamuslendssupport to the hypothesis that the parafascicularnucleus is essentially astructure receivjng thepain bearing impulsesand the centromediannucleus which receivesthe afferent impulsest'rom the poirit of acupuncture may serve as apain modulation center. A nociceptive stimulus,be it a natural painful stimulus or strongelectrical stimulation of a sensory nerve, canproduce characteristic electrical responses of theparafascicular neurons which bear all the signsof pain, viz long latent period, prolonged after-discharges, lack of adaptation and eliminabilityby morphine. The nociceptive discharges of theparafascicular neurons can be inhibited byactivation of an acupuncture point, moderateelectrical stimulation of a sensory nerve, pin-ching the Achilles tendon or direct electricalstimulation of the centromedian nucleus. Theoptimal pulse frequency for inhibition of no-ciceptive discharges of parafascicular neuronseither in aCUPuncture or in direct centromedianstimulation ranges from 4 t0 8 per second.The nociceptive discharges can be completelyarrested for about 100-170 msec following eachstimulating pulse applied to the centromediannucleus at a lower frequency. The develop-ment of this temporary inhibition necessitatesa latent period of 15-20 msec. It is thus as-sumed that the elaboration and transmission ofthe inhibitory effect on the nociceptive dis-charges of the parafascicular neurons are pro-bably achieved through a forebrain circuitconsisting of the caudate nucleus and putamenas important links. On theoretical grounds, theauthor considers a surgical lesion stereotactical-ly placed in the centromedian nucleus is pro-bably ineffective in relief of intractable pain. |
