Functional magnetic resonance imaging was performed at 1.5 Tesla in thirty healthy volunteers (15 women, 15 men) to identify cortical and subcortical regions involved in voluntary pelvic floor muscle control. Previous reports concerning the representation of these muscles in the cortex of the medial wall are inconsistent. The subjects performed rhythmical (1 Hz) contractions of the external urethral sphincter and of auxiliary pelvic floor muscles, similar as during the voluntary interruption of micturition. We found strong and consistent activity (corrected p < 0.05) in posterior parts of the supplementary motor area (SMA), adjacent to the medial primary motor cortex (M1). Further significant activations were detected bilaterally in the frontal opercula, in the right insular cortex, and right supramarginal gyrus. There were no significant gender-related differences. The representation of pelvic floor muscles in the posterior SMA and medial M1 does not follow the pattern of the classical motor homunculus. It rather seems to reflect the segmental organization of the spinal cord, where motor nuclei of sphincter muscles are located in the sacral segments S 3/4.

Supported by Deutsche Forschungsgemeinschaft (DFG grant KU1937/2-1)