Coherence is a correlation measure between frequency domain representations of different signals and CMC is conventionally used as an index of the synchronization between cortical motor regions and associated body muscles 22. Not investigated yet in the context of sensorimotor entrainment, cortico-muscular coherence (CMC) is potentially a powerful approach to address this question. Furthermore, studies using Electroencephalography (EEG) showed selectively enhanced neural activity in response to a rhythmic pattern after a movement training in which participants were trained to move at these specific frequencies marking a metrical interpretation of the rhythm 21.Īlthough there is considerable evidence for activity in motor cortices induced by auditory rhythmic stimuli, how these responses transfer at muscular level remains unclear. Magnetoencephalographic (MEG) studies also showed that listening passively to auditory rhythms modulates the amplitude of neural oscillations in the beta range (15–30 Hz) 18, 19 that are involved in movement perception and production 20. For example, the basal ganglia and supplementary motor area are activated in beat perception, and such activation is greater for musicians than non-musicians 17. Neuroimaging studies demonstrated that motor areas are activated during both rhythm perception and production 12, 13, 14, 15, 16. Previous research has provided important insights into the contribution of the motor system in the neural processing of auditory rhythms even without overt movement or the intention to move. Such entrainment supports the perception and production of complex auditory sequences, including music that are coordinated intra-personally (e.g., the two hands of a percussionist) and interpersonally (between ensemble co-performers) 10, 11. This automatic activation of the motor system in response to sensory sequences is a consequence of sensorimotor entrainment 7, 8, 9. Based on cortical and subcortical connections between the auditory and motor system, auditory inputs can entrain motor responses, as evidenced by voluntary and involuntary movement synchronisation to auditory rhythms 1, 3, 4, 5, 6. Notwithstanding, some are more conducive to synchronisation than others, such as musical rhythms or biological rhythms. It has been shown that synchronisation even occurs when instructed to avoid it or focusing on another rhythm 1, 2, 3. Human movements are spontaneously attracted by rhythmic sensory stimulation.
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This suggests that learning to bimanually produce a rhythmic musical pattern reinforces lateralised and segregated cortico-muscular communication. However, correlation analyses indicated that left- and right-hand beta EEG–EMG coherence were positively correlated over time before training but became uncorrelated after training. Results revealed no changes after training in overall beta CMC or beta oscillation amplitude, nor in the correlation between the left and right sides for EEG and EMG separately.
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During the training, participants learnt to produce the rhythmic pattern guided by visual cues by pressing the force sensors with their left or right hand to produce the low- and high-pitch sounds, respectively. Electroencephalography (EEG) and electromyography (EMG) from the left and right First Dorsal Interosseus and Flexor Digitorum Superficialis muscles were concurrently recorded during constant pressure on a force sensor held between the thumb and index finger while listening to the rhythmic pattern before and after a bimanual training session.
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Here we investigated how learning to produce a bimanual rhythmic pattern composed of low- and high-pitch sounds affects CMC in the beta frequency band. Cortico-muscular coherence (CMC) in the theta, alpha, beta and gamma frequencies has been used as an index of the synchronisation between cortical motor regions and the muscles. Human movements are spontaneously attracted to auditory rhythms, triggering an automatic activation of the motor system, a central phenomenon to music perception and production.