Abstract
Intermuscular coherence allows the investigation of common input to muscle groups. Although beta-band (15–30 Hz) intermuscular coherence is well understood as originating from the cortex, the source of intermuscular coherence at lower frequencies is still unclear. We used a wearable device that recorded electromyographic (EMG) signals during a 24-h period in four lower limb muscles of seven spinal cord injury patients (American Spinal Cord Injury Association impairment scale: A, 6 subjects; B, 1 subject) while they went about their normal daily life activities. We detected natural spasms occurring during these long-lasting recordings and calculated intermuscular coherence between all six possible combinations of muscle pairs. There was significant intermuscular coherence at low frequencies, between 2 and 13 Hz. The most likely source for this was the spinal cord and its peripheral feedback loops, because the spinal lesions in these patients had interrupted connections to supraspinal structures. This is the first report to demonstrate that the spinal cord is capable of producing low-frequency intermuscular coherence with severely reduced or abolished descending drive.NEW & NOTEWORTHY This is the first report to demonstrate that intermuscular coherence between lower limb muscles at low frequencies can be produced by the spinal cord with severely reduced or abolished descending drive.
Highlights
Intermuscular coherence is an important and useful tool in motor control studies
Beta oscillations are carried down the corticospinal tract (Baker et al 2003), and damage to this pathway leads to loss of beta-band intermuscular coherence (Fisher et al 2012)
In this study we demonstrated significant intermuscular coherence at low frequencies (2–13 Hz) during spontaneously occurring spasms in spinal cord injury patients
Summary
Intermuscular coherence is an important and useful tool in motor control studies. It can be used to investigate muscle groups receiving common input from parts of the nervous system (e.g., Nazarpour et al 2012), to assist in the diagnosis of postural tremor (van der Stouwe et al 2015) and upper motor neuron dysfunction in motor neuron disease (Fisher et al 2012), and, when combined with corticomuscular coher-ence, to differentiate between pathways converging onto spinal motoneurons (Boonstra 2013). It can be used to investigate muscle groups receiving common input from parts of the nervous system (e.g., Nazarpour et al 2012), to assist in the diagnosis of postural tremor (van der Stouwe et al 2015) and upper motor neuron dysfunction in motor neuron disease (Fisher et al 2012), and, when combined with corticomuscular coher-. Beta oscillations are carried down the corticospinal tract (Baker et al 2003), and damage to this pathway leads to loss of beta-band intermuscular coherence (Fisher et al 2012). This may have substantial clinical relevance to assist in the early diagnosis of upper motor neuron dysfunction in motor neuron disease
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