MEG Insight into the Spectral Dynamics Underlying Steady Isometric Muscle Contraction

Abstract

To gain fundamental knowledge on how the brain controls motor actions, we studied in detail the interplay between MEG signals from the primary sensorimotor (SM1) cortex and the contraction force of 17 healthy adult humans (7 females, 10 males). SM1 activity was coherent at ∼20 Hz with surface electromyogram (as already extensively reported) but also with contraction force. In both cases, the effective coupling was dominant in the efferent direction. Across subjects, the level of ∼20 Hz coherence between cortex and periphery positively correlated with the “burstiness” of ∼20 Hz SM1 (Pearson r ≈ 0.65) and peripheral fluctuations (r ≈ 0.9). Thus, ∼20 Hz coherence between cortex and periphery is tightly linked to the presence of ∼20 Hz bursts in SM1 and peripheral activity. However, the very high correlation with peripheral fluctuations suggests that the periphery is the limiting factor. At frequencies <3 Hz, both SM1 signals and ∼20 Hz SM1 envelope were coherent with both force and its absolute change rate. The effective coupling dominated in the efferent direction between (1) force and the ∼20 Hz SM1 envelope and (2) the absolute change rate of the force and SM1 signals. Together, our data favor the view that ∼20 Hz coherence between cortex and periphery during isometric contraction builds on the presence of ∼20 Hz SM1 oscillations and needs not rely on feedback from the periphery. They also suggest that effective cortical proprioceptive processing operates at <3 Hz frequencies, even during steady isometric contractions.SIGNIFICANCE STATEMENT Accurate motor actions are made possible by continuous communication between the cortex and spinal motoneurons, but the neurophysiological basis of this communication is poorly understood. Using MEG recordings in humans maintaining steady isometric muscle contractions, we found evidence that the cortex sends population-level motor commands that tend to structure according to the ∼20 Hz sensorimotor rhythm, and that it dynamically adapts these commands based on the <3 Hz fluctuations of proprioceptive feedback. To our knowledge, this is the first report to give a comprehensive account of how the human brain dynamically handles the flow of proprioceptive information and converts it into appropriate motor command to keep the contraction force steady.

Corticomuscular interactions during different movement periods in a multi-joint compound movement

“…Coherence was estimated in beta (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), gamma (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44) and high gamma (44-60 Hz) frequency bands, across all muscles (8) and periods (3), resulting in 24 variables of interest for each frequency band.…”

“…Therefore, additional partial directed coherence (PDC) analyses are essential in order to examine directionality of communication between cortex and muscles by quantifying direction of information flow (DIF) 29,30 . PDC has been used for MEG 31 , EEG 32,33 and EMG 34 recordings. Previous evidence on directionality between EEG and EMG recordings suggests patterns of directionality as well as band-specific dominant directions of information flow during motor tasks 32,35 .…”

Hearing through lip-reading: the brain synthesizes features of absent speech

“…A similar approach has been used to model brain responses to speech temporal envelope at 1-8 Hz, 56,57 and to model brain responses to natural force fluctuations occurring during maintenance of constant hand grip contraction. 58 TRFs are the direct analogue of evoked responses in the context of continuous stimulation.…”

Tidal volume and respiration phase modulate cortico-muscular communication

“…CMC in continuous data. Validating previous localisations of CMC in sensorimotor cortex (Brown, 2000;Gross et al, 2000;Kilner et al, 2000;Bourguignon et al, 2017), we first calculated coherence within continuous EMG and MEG data to extract a sensor space ROI for all further analyses. As hypothesised, the topographic distribution of CMC in the beta band (averaged from 10 -30 Hz) was focussed over contralateral (i.e., left) medio-parietal sensors (Fig.…”