Journal
JOURNAL OF NEUROSCIENCE
Volume 35, Issue 44, Pages 14708-14716Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.1971-15.2015
Keywords
EMG; fMRI; functional connectivity; motor cortex; pelvic floor; TMS
Categories
Funding
- University of Southern California Division of Biokinesiology and Physical Therapy
- Loma Linda University Physical Therapy Department
- National Center for Medical Rehabilitation Research of the National Institutes of Health [T32 HD064578]
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The human brain is believed to simplify the control of the large number of muscles in the body by flexibly combining muscle coordination patterns, termed muscle synergies. However, the neural connectivity allowing thehumanbrain to access and coordinate muscle synergies to accomplish functional tasks remains unknown. Here, we use a surprising pair of synergists in humans, the flexor hallucis longus (FHL, a toe flexor) and the anal sphincter, as a model that we show to be well suited in elucidating the neural connectivity underlying muscle synergy control. First, using electromyographic recordings, wedemonstrate that voluntaryFHLcontraction is associated with synergistic anal sphincter contraction, but voluntary anal sphincter contraction occurs without FHL contraction. Second, using fMRI, we show that two important medial wall motor cortical regions emerge in relation to these tasks: one located more posteriorly that preferentially activates during voluntary FHL contraction and one located more anteriorly that activates during both voluntary FHL contraction as well as voluntary anal sphincter contraction. Third, using transcranial magnetic stimulation, we demonstrate that the anterior region is more likely to generate anal sphincter contraction thanFHLcontraction. Finally, using a repository resting-state fMRI dataset, we demonstrate that the anterior and posterior motor cortical regions have significantly different functional connectivity with distinct and distant brain regions. We conclude that specific motor cortical regions in humans provide access to different muscle synergies, which may allow distinct brain networks to coordinate muscle synergies during functional tasks.
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