Specific modulation of corticomuscular coherence during submaximal voluntary isometric, shortening and lengthening contractions

Figures

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  Figure 1. Experimental protocol. MVC maximal voluntary contraction, 50% EMG SOL contraction intensity corresponding to 50% of the EMG obtained during maximal voluntary isometric contractions.

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  Figure 2. Effects of muscle contraction type on the soleus and the medialis gastrocnemius spinal excitability. Modulations of spinal excitability are computed with the muscle H-reflex (Hsup) normalized to the corresponding M-wave (Msup) amplitudes, in arbitrary units (a.u). Modulations of the Hsup/Msup ratio for (A) the soleus (n = 25) and (B) the medialis gastrocnemius (n = 14) are shown during lengthening (LEN), isometric (ISO) and shortening (SHO) contractions. Error bars represent the 95% CI of the mean. Lengthening vs isometric and shortening: ***p < 0.001.

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  Figure 3. Correlation between beta-band CMC and normalized H-reflex in the SOL. The relationship between beta-band CMC (SOL β-CMC Volume) and the normalized H-reflex (SOL H-reflex ratio) have been calculated in the SOL, across all participants. A significant correlation was observed between SOL β-CMC Volume and SOL H-reflex ratio (r = 0.421, p < 0.001). Data obtained during lengthening contractions (LEN) are shown in blue, during isometric contractions (ISO) in red and during shortening ones (SHO) in green. The solid line shows the estimated regression line, and the dashed lines represent its 95% CI.

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  Figure 4. Effects of muscle contraction type and muscle type on beta-band CMC. CMC was computed as the volume in the beta-band (13–32 Hz) during the last 200 ms prior to the neurostimulation onset. Modulations are shown in the soleus (grey circles) and the medialis gastrocnemius (yellow triangles) during lengthening (LEN), isometric (ISO) and shortening (SHO) contractions. Error bars represent the 95% CI of the mean (n = 25). Lengthening vs isometric in SOL: ***p < 0.001; SOL vs MG during lengthening: $p < 0.01.

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  Figure 5. Effects of muscle contraction type on gamma-band CMC. CMC was computed as the volume in the gamma-band (33–52 Hz) during the last 200 ms prior to the neurostimulation onset. Modulations are shown in the soleus (grey circles) and the medialis gastrocnemius (yellow triangles) during lengthening (LEN), isometric (ISO) and shortening (SHO) contractions. Error bars represent the 95% CI of the mean (n = 25). Lengthening vs isometric: ***p < 0.01; shortening vs isometric: $p < 0.01.

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  Figure 6. Illustration of the different steps involved in the calculation of time–frequency wavelet-based corticomuscular coherence during shortening contractions, preceded by a period of isometric preactivation, in a typical subject. The pink vertical dashed lines represent the 200 ms window preceding the neurostimulation chosen for the analyse. First row: mean wavelet auto-spectra of the EMG time series from the soleus (A) and the Cz EEG (B). Second row: wavelet cross-spectrum between the soleus EMG and the Cz EEG time series; the red contours identify the areas in the time–frequency plane where the correlation between the soleus EMG and the Cz EEG signals is statistically significant (C). Third row: wavelet magnitude-squared coherence between the soleus EMG and the Cz EEG time series where the correlation between the soleus EMG and the Cz EEG signals is statistically significant. The pink horizontal solid lines represent the [13–32] beta-band. (D) In each frequency band (β: 13–32 Hz; γ: 33–52 Hz), the corticomuscular coherence value was defined as the volume under the magnitude-squared coherence values in the 0.2-s time window of interest preceding the neurostimulation, where the…