Human brain activation under controlled thermal stimulation and habituation to noxious heat: An fMRI study

Brain activity was studied with functional magnetic resonance imaging (fMRI) following thermal stimulation. Two groups (n = 6/group) of human male volunteers were given up to four noxious (46°C) and four non‐noxious (41°C) stimuli. In the 46°C experiment, positive signal changes were found in the frontal gyri, anterior and posterior cingulate gyrus, thalamus, motor cortex, somatosensory cortex (SI and SII), supplementary motor area, insula, and cerebellum. Low‐level negative signal changes appeared in the amygdala and hypothalamus. All regions activated by 46°C were also activated by 41°C. However, except for SI and thalamus, significantly more activation was observed for the 46°C stimulus. A significant attenuation of the signal change was observed by the third stimulus for the 46°C, but not for 41°C experiment. Similar findings were replicated in the second group. These fMRI findings specify differences between somatosensory and pain sensation and suggest a number of rich avenues for future research. Magn Reson Med 41:1044–1057, 1999. © 1999 Wiley‐Liss, Inc.