Brain activation during micturition in women.

Experiments in the cat have led to a concept of how the CNS controls micturition. In a previous study this concept was tested in a PET study in male volunteers. It was demonstrated that specific brainstem and forebrain areas are activated during micturition. It was unfortunate that this study did not involve women, because such results are important for understanding urge incontinence, which occurs more frequently in women than in men. Therefore, a similar study was done in 18 right-handed women, who were scanned during the following four conditions: (i) 15 min prior to micturition (urine withholding); (ii) during micturition; (iii) 15 min after micturition; and (iv) 30 min after micturition. Of the 18 volunteers, 10 were able to micturate during scanning and eight were not, despite trying vigorously. Micturition appeared to be associated with significantly increased blood flow in the right dorsal pontine tegmentum and the right inferior frontal gyrus. Decreased blood flow was found in the right anterior cingulate gyrus during urine withholding. The eight volunteers who were not able to micturate during scanning did not show significantly increased regional cerebral blood flow in the right dorsal, but did so in the right ventral pontine tegmentum. In the cat this region controls the motor neurons of the pelvic floor. In the same unsuccessful micturition group, increased blood flow was also found in the right inferior frontal gyrus. In all 18 volunteers, decreased blood flow in the right anterior cingulate gyrus was found during the period when they had to withhold their urine prior to the micturition condition. The results suggest that in women and in men the same specific nuclei exist in the pontine tegmentum responsible for the control of micturition. The results also indicate that the cortical and pontine micturition sites are more active on the right than on the left side.