Cerebral topography of rectal stimulation using single photon emission computed tomography.

Central processing of visceral information in humans is incompletely understood. We aimed to demonstrate the feasibility of single photon emission computed tomography (SPECT) and to quantitate the changes in regional cerebral blood flow during rectal distension. Ten healthy volunteers underwent randomized sham and active rectal distensions on separate days, during which cerebral blood flow was assessed by intravenous technetium-99m ethyl cysteinate dimer (99mTc-ECD) SPECT. Three-dimensional coregistration of brain images was used to quantitate activation in four preselected cerebral foci and two control regions. Paired analysis compared blood flow during sham and active distensions. There was increased right anterior cingulate gyrus activity (6.5 ± 2.9%, P = 0.03) with active rectal distension. A 5.4 ± 2.4% reduction in blood flow in the superior parieto-occipital control region ( P = 0.04) suggested blood "redistribution" during stimulation. Marked variability in activation of the frontal cortex, thalamus/basal ganglia complex, and mesiotemporal lobe was noted. Thus rectal distension increases activity in the right anterior cingulate gyrus on average; other foci of cerebral activation are quite variable, suggesting a lack of specific cerebral projections during rectal stimulation.