Home Publications Identification of common synaptic inputs to motor neurons from the rectified electromyogram
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D. Farina, F. Negro, and N. Jiang (2013)

Identification of common synaptic inputs to motor neurons from the rectified electromyogram

The Journal of Physiology 591(10):2403-2418.  (export entry)

BFNT-Chair Neuroinformatics
Oscillatory common inputs of cortical or peripheral origin can be identified from themotor neuron output with coherence analysis. Linear transmission is possible despite the motorneuronnon-linearitybecausethesameinputissentcommonlytoseveralneurons.Becauseofthelinear transmission, common input components to motor neurons can be investigated from thesurface EMG, for example by EEG–EMG or EMG–EMG coherence. In these studies, there is anopen debate on the utility and appropriateness of EMG rectification. The present study addressesthis issue using an analytical, simulation and experimental approach. The main novel theoreticalcontributionthatwereportisthatthespectraofboththerectifiedandtherawEMGcontaininputspectral components to motor neurons. However, they differ by the contribution of amplitudecancellation which influences the rectified EMG spectrum when extracting common oscillatory inputs.Therefore,thedegreeofamplitudecancellationhasanimpactontheeffectivenessofEMGrectificationinextractinginputspectralpeaks.Thetheoreticalpredictionswereexactlyconfirmedby realistic simulations of a pool of motor neurons innervating a muscle in a cylindrical volumeconductorof EMG generation and by experiments conducted on the first dorsal interosseous andthe abductor pollicis brevis muscles of seven healthy subjects during pinching. It was concludedthatwhenthecontractionlevelisrelativelylow,EMGrectificationmaybepreferableforidentifyingcommon inputs to motor neurons, especially when the energy of the action potentials in the low frequency range is low. Nonetheless, different levels of cancellation across conditions influencethe relative estimates of the degree of linear transmission of oscillatory inputs to motor neuronswhen using the rectified EMG.
DOI: 10.1113/jphysiol.2012.246082