Brain activation by thermal stimulation in humans studied with fMRI

Abstract

Sensations evoked by innocuous thermal stimulation can be divided into two categories. One is “temperature sensation” in a narrow sense, which is directed towards an object outside the body. The other is the “thermal comfort/discomfort” of the body that is important for thermoregulation. We recently reported rCBF changes in the amygdala which correlated with thermal comfort during whole body cooling (Kanosue et al. , 2000). In the present study we investigated the region of brain that is activated by local thermal stimulation of the hand. Eight healthy subjects were recruited and gave written informed consent to participate in the study. Warm (39°C) or cold (25°C) stimuli was applied to the right or left hand for 30 s by using a water circulating tube that covered the whole hand. Each subject reported the magnitude of the stimulus intensity of temperature sensation using a scale from 1 (very cold) to 9 (very hot). All subjects reported hot or cold sensations and not pain. We examined the correlation between the rating scores and regional activity over the entire brain with a 3 Tesla MR imagers (VP, General Electrics, Milwaukee, US). Activation was observed in the contralateral secondary somatosensory cortex in response to both warm and cold stimulation of the hand. No activation was observed in the amygdala. This suggests that temperature sensation and thermal comfort might be generated by completely different structures of the brain.