title: Between-subject variance in the magnitude of corticomuscular coherence during tonic isometric contraction of the tibialis anterior muscle in healthy young adults.
abstract: Oscillatory activity of the sensorimotor cortex has been reported to show coherence with muscle activity in the 15- to 35-Hz frequency band (β-band) during weak to moderate intensity of isometric contraction. The present study examined the variance of the magnitude of the corticomuscular coherence across a large number of subjects. We quantified the coherence between EEG over the sensorimotor cortex and rectified electromyogram (EMG) from the tibialis anterior muscle during tonic isometric contraction at 30% of maximal effort in 100 healthy young individuals. We estimated the maximal peak of EEG-EMG coherence (Cohmax) and the ratio of the sum of the autopower spectral density function within the β-band to that of all frequency ranges for both EEG (EEGβ-PSD) and EMG (EMGβ-PSD) signals. The frequency histogram of Cohmax across all subjects showed a broad bell-shaped continuous distribution (range, 0.048-0.816). When the coherence was thresholded at the estimated significance level of P < 0.05 (0.114), 46 out of 100 subjects showed significant EEG-EMG coherence. Cohmax occurred within the β-band in the majority of subjects who showed significant EEG-EMG coherence (n = 43). Furthermore, Cohmax showed significant positive correlations with both EEGβ-PSD (r = 0.575, P < 0.001) and EMGβ-PSD (r = 0.606, P < 0.001). These data suggest that even during simple tonic isometric contraction, the strength of oscillatory coupling between the sensorimotor cortex and spinal motoneurons varies among individuals and is a contributory factor determining muscle activation patterns such as the degree of grouped discharge in muscle activity within the β-band for each subject.
authors.affiliation: Department of Rehabilitation Medicine, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Ushiyama
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Suzuki
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Masakado
authors.forename: Kimitaka
authors.initials: K
authors.lastname: Hase
authors.forename: Akio
authors.initials: A
authors.lastname: Kimura
authors.forename: Meigen
authors.initials: M
authors.lastname: Liu
authors.forename: Junichi
authors.initials: J
authors.lastname: Ushiba
mesh_terms: D000328:Adult; D000367:Age Factors; D004569:Electroencephalography / Q000379:methods; D004576:Electromyography / Q000379:methods; D005260:Female; D014644:Genetic Variation / Q000502:physiology*; D006304:Health Status; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D055815:Young Adult