Cerebral evoked responses to skin warming recorded from human scalp

Reponses evoked by warming the glabrous palmar skin were recorded maximally from a contralateral parietal scalp site that approximated the hand projection area of sensorimotor cortex. A smaller and later occurring response was also seen at the corresponding ipsilateral site. The temperature to which the skin was adapted was critical and was maintained at 35 degrees C rather at 30 degrees C as it was in an earlier study where no responses were seen. Peak latencies ranged from 280 msec to 356 msec for stimulus intensities of 8 degree C presented at a rate of 19 degrees C/sec. This warm evoked response appeared to have its origin in the specifically sensitive primary warm afferents. The presence of an evoked response when warming occurred from the 35 degrees C adapting temperature (AT) and its absence at the 30 degrees C AT coincide with the greater sensitivity of warm receptors at the higher AT. Comparison of these results with those for evoked responses to skin cooling and tactile tap suggest that the cortical organization of temperature (both warm and cool stimuli) in human is similar to that of touch.