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Information flow from the sensorimotor cortex to muscle in humans.
T Mima1, T Matsuoka, M Hallett
1Human Motor Control Section, NINDS, National Institutes of Health, MSC1428, Bethesda, MD 20892-1428, USA.
Summary
Human electroencephalogram-electromyogram (EEG-EMG) coherence reveals directional information flow from EEG to EMG in the gamma band, suggesting distinct mechanisms for higher frequencies and motor control commands.
Area of Science:
- Neuroscience
- Motor Control
- Biomedical Engineering
Background:
- Understanding the physiological mechanisms of electroencephalogram-electromyogram (EEG-EMG) coherence is crucial for interpreting neural control of movement.
- Previous studies have explored EEG-EMG coupling, but the specific directional information flow and its frequency dependence remain areas of active investigation.
Purpose of the Study:
- To investigate the physiological mechanisms underlying human EEG-EMG coherence.
- To determine the directionality of information transfer between EEG and EMG signals during tonic muscle contraction using the Directed Transfer Function (DTF).
Main Methods:
- Recorded 56-channel EEG and EMG from the right abductor pollicis brevis muscle in 6 healthy volunteers during weak tonic contraction.
- Computed EEG-EMG coherence and DTF using EEG from the sensorimotor area and rectified EMG.
- Utilized a multivariate autoregressive (MVAR) model for DTF computation.
Main Results:
- EEG-EMG coherence peaked between 15-29 Hz (mean 18.5 Hz).
- DTF analysis revealed a peak information flow from EEG to EMG at 12-27 Hz (mean 17.8 Hz).
- Significantly greater DTF from EEG to EMG compared to EMG to EEG was observed at 19-30 Hz and 45-50 Hz (P<0.05).
Conclusions:
- The findings suggest distinct EEG-EMG coupling mechanisms for frequencies above and below 19 Hz.
- Directional information flow from EEG to EMG in higher frequencies (19 Hz and above) likely represents motor commands.
- Gamma band (e.g., 40 Hz) EEG-EMG coherence indicates motor control commands, not solely specific to muscle rhythms like Piper rhythm seen in strong contractions.