ASSESSING THE MODULATION OF CORTICAL BETA OSCILLATIONS IN RELATION TO NATURAL FORCE FLUCTUATIONS USING PERIPHERAL RECORDINGS

Background: During isometric contractions, cortical beta oscillations modulate the excitability of motor neurons, and doing so, leave a trace in electromyographic or contraction force signals. Previous studies aiming to capture the modulation of beta oscillations in force signals relied on a task combining an isometric contraction with transient movements, but such a task is challenging for individuals with motor impairments. Notably, during isometric muscle contraction, beta oscillations modulate in relation to natural force fluctuations.
Aim: Here, we test the hypothesis that similar modulations are present in the force.
Methods: We analysed MEG and force data from 17 healthy adults who performed a low-force (2–4 N) isometric pinch grip with their right hand. Power modulations were computed by averaging the instantaneous power of MEG signals collected above the left primary sensorimotor cortex and force signals weighted by temporally shifted (from –2 to 2 s) signals that capture the rate of force increase or the presence of low-plateaus. Statistical significance of power modulation was assessed using surrogate-data-based statistics. Finally, Pearson correlation assessed the relationships between MEG and force modulations.
Results: Power modulations in the beta band were observed in two signals in relation to both force features in >75 % of the participants (p < 0.001). There were significant and positive correlations between MEG and force modulations at maximum power across beta frequencies (r = 0.81-0.86; p < 0.001).
Conclusions: Our findings demonstrate that force signal can be used as a proxy for cortical beta oscillations during isometric contractions.