Modulation of beta oscillatory dynamics in motor and frontal areas during physical fatigue

Figures

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  Fig. 1. Experimental protocol and individualized beta-band computation. A Procedure. All participants performed 100 contractions during two separate sessions (S). Each contraction lasted 10 or 12 s, depending on the session (S10 and S12, respectively), and was separated by a fixed rest time (5 s). EMG and EEG activity were recorded during the 100 contractions. Before and after the task, Maximal Voluntary Contractions (MVC, ~3 s) and long MVC (~30 s) were performed to assess the fatigue generated by the 100 contractions. Resting State (RS) EEG (3 min) was recorded before and after the task to quantify the associated EEG correlates. B Spectrogram representations of Cz electrode for two typical participants (P) in the S12 session. Each plot represents the median over 100 contractions after a baseline correction between the −3 to −1 s period preceding the contraction (contraction onset = 0 s). Magenta rectangles represent the individualized beta band, which ranges from −2 to +2 Hz around the frequency with the largest desynchronization in the period of interest (2–10 s) for each participant. Note that Iβ was computed accounting for both S10 and S12 sessions (see “Methods” for details). Only…

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  Fig. 2. Neuromuscular fatigue assessment and beta-band power modulations. A Neuromuscular Pre-Post Variation Rates (VR). A decrease in Maximal Voluntary Torque (MVT) reflects a decline in the maximal force production, while a reduction in Long Max Integral reveals a decline in the ability to sustain a maximal force over a given duration (30 s here). Both measurements allow for the assessment of physical fatigue. B EMG and EEG modulations over the main task. Panel 1 represents the EMG expressed in normalized RMS over contractions, whose increase reflects neuromuscular fatigue accumulation. Panels 2 and 3 represent relative power changes (respective to the first contractions, see “Methods” for details) quantified in an Individualized-Beta band (Iβ) in Cz, in contraction (panel 2), and at rest (panel 3), that is, between contractions. Panel 4 exhibits the power-relative changes in frontal electrodes quantified during contractions. The dots represent the averaged distribution for all panels, and the error bars are the standard error mean (SEM). C EMG and Iβ Cz during contractions. The lines represent the average over participants of EMG and Iβ Cz during a contraction, with their SEM in…

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  Fig. 3. Beta-band power modulations in low and high-beta bands. A β Power Spectrum. A wide β Power Spectrum (12–40 Hz) is represented on the upper panel for the first (B1) and last (B10) bin of each session. The lower panel represents the difference between the last and first bin for each session. For both panels, the lines represent the average over participants and the shaded areas the SEM. B Motor areas. All panels represent the relative power changes over the 100 contractions (respective to the first contractions, see “Methods” for details) quantified in Cz in Low-Beta (Lβ) and High-Beta (Hβ) during contractions (panels 1 and 2) and at rest (panels 3 and 4). C Frontal areas. The panels display Lβ and Hβ power relative changes over the 100 contractions, quantified in frontal electrodes during contractions. For (B, C), the dots represent the averaged distribution, and the error bars the SEM.

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  Fig. 4. Functional and effective connectivity. A Correlations. Within subjects’ correlations were performed between Iβ Cz and EMG, and Iβ Cz and Iβ Frontal, for each session independently. The resulting r values were then compared using t-tests. B Granger causality (GC). GC was performed to assess the relative changes in the bidirectional information flow between motor and frontal areas, and between motor areas and EMG. Each bin results from the integration of 20 contractions. The dots represent the averaged distribution, and the error bars the SEM. The first bin is 0 centered for both sessions.

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  Fig. 5. Relation between beta-band modulations during resting-state and in contraction. A Schematic representation of Beta evolution. “RS” stands for Resting-State (Baseline power). “Act.” stands for activation, which reflects the necessary activation threshold (beta desynchronization threshold) needed to perform the contraction at the required intensity. The double vertical arrows represent the amount of desynchronization for each group. Considering two hypothetical groups that have different (low (L) or high (H)) relative changes between the Pre and Post RS beta-band power, we might expect to find a larger desynchronization for the H group. In other words, the larger the increase in beta-band power RS after the task, the larger the desynchronization during the contractions. B Iβ Cz over bins for each group and each session. The participants were divided into two groups (L Iβ Post and H Iβ Post) according to a median split performed on the Iβ power RS pre-post variation rate. Then, we represented the Iβ power evolution during contractions for these two groups. The dashed line represents the participants’ average, the shaded area the SEM, and the solid line, a polynomial fit with 3…

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  Fig. 6. Spiking network model of beta-band desynchronization during physical fatigue. A Spiking network and beta-band modulations. The upper part of the panel illustrates the 1000 interconnected Izhikevich neurons, 80% excitatory and 20% inhibitory, with its averaged spiking activity represented in the middle part of the panel. The lower part of the panel displays the beta-band power generated by the spiking network and modulated over time. The contraction period (from 1500 to 2000 ms) corresponds to an excitatory modulation sent for 500 ms to a subset of excitatory and inhibitory neurons. As we can see on the lower part of the panel, a desynchronization occurs during the excitatory input (green area). The five Bins (B) represent an incremental number of recruited neurons (from Bin 1 to Bin 5) to simulate the fatigue effect. B Typical time-frequency map. The network generates beta power centered around 25 Hz, followed by a desynchronization and a slight rebound at the end of the movement. C Beta-band power modulations. This panel represents the relative power changes quantified during the “movement” period over Bins. The dots represent the averaged distribution of the 10 simulations, and…