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

Asavasopon S, Rana M, Kirages DJ, Yani MS, Fisher BE, Hwang DH, Lohman EB, Berk LS, Kutch JJ.  The Journal of Neuroscience, 10-8-14. 34(41):13811–13818

Trisha Jenkyns PT, DPT, WCS

11-5-2014   Pelvic PT Distance Journal Club

 

OBJECTIVE

The purpose of this study was to look the connection between the brain and the pelvic floor & pelvic floor synergies.

·         The authors hypothesized that, if the motor cortex is associated with pelvic muscle synergies, there would be a medial wall region in the brain that was active during voluntary pelvic floor activation and voluntary activation of synergists, and that moreover, stimulation of this region would generate pelvic floor activation.

·         Overview: First, EMG was first used to define PFM synergies.  Second, fMRI was used to define the part of the brain that is associated with the synergies.  Third, transcranial stimulation was then done to confirm that the fMRI-identified medial wall region is ‘likely’ to generate pelvic floor muscle activation

MATERIALS & METHODS

·         Participant population: 16 healthy males (physical therapists or physical therapy students with general knowledge of pelvic floor anatomy and function) were recruited.  Mean age 32.63 (range: 24–43 years).  The studies were performed at the University of Southern California

·         First: In 10 participants muscle contractions were measured using EMG to define the PFM synergies and to verify the previously reported muscle synergy between the PFM and gluteus maximus muscle (GMM) and to establish finger muscle activation as an appropriate control muscle group that does not have synergistic coupling with the PFM muscles.

·         Men were in supine position inside a mock MRI scanner…they recorded surface EMG data from the right Gluteus Maximus m (GMM), the PFM, and the right first dorsal interosseous muscle (FDI).

·         Equipment used:

o   GMM and FDI EMG: miniature electrode/preamplifiers (DELSYS) with two silver recording surfaces

o   PFM EMG: rectal sensor, Pathway- Prometheus.

·         Instructions given:

o   PFM trials, participants were instructed to contract their PFM as if to stop the flow of urine.

o   GMM trials, participants were instructed to isometrically contract their GMM.

o   FDI trials, participants were instructed to contract their FDI muscle to generate index finger abduction.

·         For all trials, maximal voluntary contraction (MVC) was 1^st determined

·         During subsequent trials, participants activated the appropriate muscle group according to an audio tone to guide the participant through a smooth activation over a period of 2 s. Each trial consisted of two sets of 10 reps, each contraction/activation lasting 2 s.

·         Because of the plan to repeat voluntary activation trials in the fMRI scanner without EMG, the participants were instructed to produce moderate muscle activation (~20% effort) to avoid fatigue during the EMG portion of the study that was performed in the mock MRI

o   These contractions were quantified & expressed as % MVC

·         EMG data was analyzed, so synergies could be identified

o   The contraction onset time

o   Other EMG signals occurring at same time

·         Second: fMRI was used to measure brain activation in 14 participants

·         Participants voluntarily contracted each muscle group (~20% effort) as described in the EMG portion of study.

·         Participants also performed an additional 6 sets of 10 reps 14 did PFM runs, 12 did GMM runs % 10 did FDI runs

·         Third: Motor cortex was stimulated using transcranial magnetic stimulation (TMS) in 8 participants and evoked potentials of the PFM were obtained.

RESULTS

·         They found PFM was activated during voluntary activation of the PFM & voluntary GMM activation, but not during voluntary activation of the FDI.

·         Figure 1B shows data from one participant during repeated activation of PFM, the GMM remained inactive, but when the participant activated the GMM, the PFM activated synchronously.  This was true across all of the participants and is represented in the group data in Figure 1C.

·         Figure 1E: It was observed that PFM activation actually occurred in advance of GMM activation during voluntary GMM activation.   Activation in PFM led GMM activation by an average of 128 ms, which proved to be significantly greater than 0 (maximum of 239.5 ms and minimum of 30.5 ms, t test, p 􏰃 0.001).

·          “A correlation analysis of PFM activity as a function of GMM activity during GMM tasks revealed a slight positive correlation, which did not reach statistical significance across the participants we studied”

·         Using fMRI data, they found that a region in the precentral gyrus was activated during voluntary PFM activation and voluntary GMM activation , but not during FDI activation.

·         Using MEP data generated by the TMS the authors were able to verify that the medial wall of the precentral gyrus is likely associated with PFM activation (this was also identified by the fMRI)

LIMITATIONS

·         PFM was represented by the electrical activity of the anal sphincter, but PFM are not a single muscle group.

·         This study was limited to only low intensity muscle contractions

·         Small sample size and only young men with healthy PFM

·         It is unclear where the sensor was exactly placed on the gluteal maximus and this is an important consideration when defining muscle synergies

DISCUSSION

Results indicate that motor areas of the cerebral cortex may be associated with the synergistic activation of the pelvic floor that has been shown to accompany voluntary activation of hip and trunk muscles 

·         The identified region appears to contain a clear contribution from the supplementary motor area.

·         “Numerous previous studies have demonstrated the importance of SMA during voluntary activation of the pelvic floor (Blok et al., 1997; Zhang et al., 2005; Seseke et al., 2006; Schrum et al., 2011).”

·         “The SMA is generally thought to be involved in higher-order organization and preparation of voluntary movement (Cunnington et al., 1996).”

·         The author’s cortical mapping results of the PFM appear to coincide with SMA proper.

·         The authors clearly state that future work needs to be done to determine whether the cortical activation they identified actually reflects cortical structuring of the PFM synergy

·         The last thing discussed by the authors is how they see potential clinical implications for understanding the motor cortical mechanisms of chronic pelvic pain.  A recent study by Kilpatrick et al., 2014 showed that patients with interstitial cystitis/painful bladder syndrome (IC/PBS) showed significant changes in resting state neural activity in the medial wall of SMA compared with healthy controls.

o   The motor cortical region (associated with PFM activation) identified by Asavasopon et al. clearly overlaps with the coordinates reported by Kilpatrick et al. in patients with IC/PBS.  Asavasopon et al. therefore conclude that their results “may suggest that changes in motor cortical areas that influence pelvic floor motor neuron pools may play a critical role in IC/PBS pathophysiology.”