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Manipulation of peripheral neural feedback loops alters human corticomuscular coherence

Lookup NU author(s): Professor Stuart Baker

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Abstract

Sensorimotor EEG shows ∼20 Hz coherence with contralateral EMG. This could involve efferent and/or afferent components of the sensorimotor loop. We investigated the pathways responsible for coherence genesis by manipulating nervous conduction delays using cooling. Coherence between left sensorimotor EEG and right EMG from three hand and two forearm muscles was assessed in healthy subjects during the hold phase of a precision grip task. The right arm was then cooled to 10°C for ∼90 min, increasing peripheral motor conduction time (PMCT) by ∼35% (assessed by F-wave latency). EEG and EMG recordings were repeated, and coherence recalculated. Control recordings revealed a heterogeneous subject population. In 6/15 subjects (Group A), the corticomuscular coherence phase increased linearly with frequency, as expected if oscillations were propagated along efferent pathways from cortex to muscle. The mean corticomuscular conduction delay for intrinsic hand muscles calculated from the phase-frequency regression slope was 10.4 ms; this is smaller than the delay expected for conduction over fast corticospinal pathways. In 8/15 subjects (Group B), the phase showed no dependence with frequency. One subject showed both Group A and Group B patterns over different frequency ranges. Following cooling, averaged corticomuscular coherence was decreased in Group A subjects, but unchanged for Group B, even though both groups showed comparable slowing of nervous conduction. The delay calculated from the slope of the phase-frequency regression was increased following cooling. However, the size of this increase was around twice the rise in PMCT measured using the F-wave (regression slope 2.33, 95% confidence limits 1.30 - 3.36). Both afferent and efferent peripheral nerves will be slowed by similar amounts following cooling. The change in delay calculated from the coherence phase therefore better matches the rise in total sensorimotor feedback loop time caused by cooling, rather than just the change in the efferent limb. A model of corticomuscular coherence which assumes that only efferent pathways contribute cannot be reconciled to these results. The data rather suggest that afferent feedback pathways may also play a role in the genesis of corticomuscular coherence. © The Physiological Society 2005.


Publication metadata

Author(s): Riddle CN, Baker SN

Publication type: Article

Publication status: Published

Journal: Journal of Physiology

Year: 2005

Volume: 566

Issue: 2

Pages: 625-639

ISSN (print): 0022-3751

ISSN (electronic): 1469-7793

Publisher: Wiley-Blackwell Publishing Ltd.

URL: http://dx.doi.org/10.1113/jphysiol.2005.089607

DOI: 10.1113/jphysiol.2005.089607

PubMed id: 15919711


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