HEAT PAIN INCREASES THE PERCEIVED MAGNITUDE OF AN INNOCUOUS ELECTRICAL STIMULUS - EVIDENCE FOR A PERIPHERAL MECHANISM

Painful heat produced an increase in the perceived magnitude of an inn ocuous electrical stimulus applied either to the sural nerve or to the skin of the dorsum of the foot. The increased sensitivity was observe d when the painful heat was spatially coincident with the electrical s timulus, and when it was not coincident but adjacent within the same d ermatome. Painful heat had no effect when it was applied to the contra lateral foot, which makes it unlikely that attention or arousal played any role in the increased electrical sensitivity produced by ipsilate ral heat. The painful heat also produced an increase in the amplitude of the sural nerve compound action potential (CAP). The heat-pain-rela ted changes in the CAP and subjective magnitude ratings were in the sa me direction, which suggests that the latter were due at least in part to a temperature-dependent change in the electrical sensitivity of th e peripheral afferents.