Cortical Control of Pelvic Musculature: Stimulation and Functional Imaging

Human pelvic floor musculature is made up of several skeletal muscles with a wide variety of mechanical functions. Pelvic muscles are unique in that they maintain an active contraction, even at rest [1]. This baseline activity is increased in patients with urological chronic pelvic pain disorders (UCPPS) [2,3], and may interfere with function and generate pain. UCPPS patients may have abnormal central nervous system activity [4], but potential impairment sites that might upregulate pelvic muscle activity have not been identified. To better understand the potential cortical contributions to pelvic muscle activity, we present a study to identify the neural substrates that mediate voluntary and involuntary pelvic muscle contraction. Previous transcranial magnetic stimulation (TMS) studies have shown that the stimulation of medial regions of primary motor cortex (M1) leads to pelvic muscle contraction [5]. However, functional magnetic resonance imaging (fMRI) studies have found the predominant activation of supplementary motor areas (SMA) during voluntary pelvic muscle contractions with only sporadic reports of M1 activation [6,7]. In this study, we use TMS to show that either medial M1 or SMA activation is likely sufficient to cause an involuntary pelvic floor contraction. We additionally use fMRI to show that medial M1 and SMA are likely involved in voluntary pelvic floor contraction.