Thalamic relay site for cold perception in humans.

The neural pathways subserving the sensation of temperature are virtually unknown. However, recent findings in the monkey suggest that the sensation of cold may be mediated by an ascending pathway relaying in the posterior part of the thalamic ventromedial nucleus (VMpo). To test this hypothesis we examined the responses of neurons to thermal stimulation of the skin and determined the perceptual effects of microstimulation in the VMpo region in awake patients undergoing functional stereotactic surgery. In 16 patients, microstimulation in the VMpo region evoked cold sensations in a circumscribed body part. Furthermore, at some of these sites thalamic neurons were found that responded to innocuous cooling of the skin area corresponding to the stimulation-evoked cold sensations. These data provide the first direct demonstration of a pathway mediating cold sensation and its location in the human thalamus.