Responses of neurons in parafascicular nucleus to severe radiant heat stimulation

On radiant heat stimulation of the sole of the hind foot of rat, the neurons in the parafascicular nucleus of thalamus would not respond until the skin temperature was raised to 45 degrees C. If there had been existing discharges in these neurons prior to the test, these discharges may be inhibited by the innocuous heat stimulus at temperatures below 45 degrees C. The warmth, or the heat below the innocuous level was unable not only to produce but also to inhibit the nociceptive neuronal discharges incurred by previous nocuous stimulation. This phenomenon is regarded as a manifestation of one of the general principles on which the interpretation of acupuncture analgesia is based.