Cortical Activation Associated with Muscle Synergies of the Human Male Pelvic Floor

Abstract

Human pelvic floor muscles have been shown to operate synergistically with a wide variety of muscles, which has been suggested to be an important contributor to continence and pelvic stability during functional tasks. However, the neural mechanism of pelvic floor muscle synergies remains unknown. Here, we test the hypothesis that activation in motor cortical regions associated with pelvic floor activation are part of the neural substrate for such synergies. We first use electromyographic recordings to extend previous findings and demonstrate that pelvic floor muscles activate synergistically during voluntary activation of gluteal muscles, but not during voluntary activation of finger muscles. We then show, using functional magnetic resonance imaging (fMRI), that a region of the medial wall of the precentral gyrus consistently activates during both voluntary pelvic floor muscle activation and voluntary gluteal activation, but not during voluntary finger activation. We finally confirm, using transcranial magnetic stimulation, that the fMRI-identified medial wall region is likely to generate pelvic floor muscle activation. Thus, muscle synergies of the human male pelvic floor appear to involve activation of motor cortical areas associated with pelvic floor control.

Brain white matter changes associated with urological chronic pelvic pain syndrome: multisite neuroimaging from a MAPP case–control study

“…Specifically, the corticospinal ROI exhibiting UCPPS-specific increases in FA overlapped with (a) the premotor region thought to encode voluntary pelvic floor muscle activity [1], as well as (b) the primary motor cortex region displaying altered whole-brain functional connectivity in men with UCPPS [37]. Furthermore, this tract directly traversed an area associated with heightened low frequency power in women with IC/BPS, based on resting state functional scan data [36].…”

“…UCPPS-related corticospinal abnormalities may therefore reflect an ongoing refinement and strengthening of motor connections that are relevant to pelvic pain, rather than a selective sparing of this tract. In particular, the correlations between corticospinal FA in M1, pelvic pain severity, and sensory qualities of pain, as well as the close proximity of this tract segment to a region strongly implicated in voluntary pelvic floor motor control [1], implies that increased regional FA may be the product of experience-dependent reinforcement (or perhaps overuse) of pain-related pelvic motor responses. Given that motor learning requires the presence of newly myelinated axons [39], it can be reasoned that pelvic pain-related motor learning is also accompanied by enhanced myelination of axons (and therefore FA) in the activated neural circuit.…”

Altered brain connectivity in dysmenorrhea

“…Recent anatomical connectivity studies in rats using the retrograde transneuronal labelling studies suggest that visceral structures may be more strongly represented in medial brain motor areas than any other cortical area; also, the visceral representation in motor cortex is aligned with the more medial somatic motor representation of trunk and lower limb muscles [12]. In humans, muscles such as the pelvic floor [1], abdominals [15], and toes [14] are represented in more medial areas of motor cortex, and dysfunction of these regions has been suggested in chronic pain [8]. These data collectively suggest that medial brain motor areas may have important, but underrecognized modulatory influence on both somatic and visceral processes.…”

Brain Connectivity Associated with Muscle Synergies in Humans

“…We selected 48 participants based on age and sex matching with the 14 participants recruited in our fMRI experiments. Data were preprocessed according to methods described previously (Roy et al, 2009;Baliki et al, 2012). At the individual-participant level, we then performed a functional connectivity analysis by contrasting the wholebrain connectivity of signals derived from the A-motor and P-motor ROIs, described above.…”

“…Pelvic floor muscles contract automatically with trunk and lower limb muscles that are distinct from the pelvic floor as follows: shoulder muscles (Hodges et al, 2007), gluteal muscles (Bø and Stien, 1994), abdominal muscles (Hodges et al, 2007), and toe muscles (Sapsford et al, 2010), presumably to promote continence and provide spinal support during functional tasks. However, lower limb muscles need not be activated during voluntary pelvic floor muscle contraction (Bø and Stien, 1994;Schrum et al, 2011;Asavasopon et al, 2014), suggesting that lower limb muscles and pelvic floor muscles are recruited as part of at least two different muscle synergies. We therefore hypothesized that there is a motor cortical synergy access point that more directly activates pelvic floor muscles compared with pelvic floor synergists, and that this access point preferentially connects to brain regions known to be involved in continence control (Fowler et al, 2008;Tadic et al, 2012).…”