Rhythm perception and sensory-motor synchronisation
How dynamic inputs entrain brain activity to build our internal representation of the external world is one of the most challenging problems currently confronting cognitive neurosciencists. This project investigates phenomena of sensorimotor synchronization and dynamic multisensory integration by taking advantage to a specific context: musical rhythm. Entrainment to music differs from other behaviors such as speech in terms of the ubiquity of its expression across human societies, and its early development in the lifespan and in human evolution. A fundamental feature of music is rhythmic movement, which is often timed with respect to a regular pulse-like beat, reflecting the intimate coupling of auditory-motor brain processes.
To investigate the neural mechanisms underlying these phenomena, we developed an EEG approach based on the hypothesis that humans perceive the beat by synchronizing large pools of neurons at the beat frequency. This approach allows to tag and disentangle the neural activities related to auditory and sensorimotor processes, by concentrating those signal of interests on specific frequencies in the EEG spectrum. Furthermore, by directly comparing the spectrum of the rhythmic input with the EEG output, these frequency-tagging studies have shown that neural responses transform rhythmic inputs by amplifying frequencies coinciding with the perceived beat frequency. Importantly, a recent study provided key evidence regarding the functional significance of this rhythmic input-output transform by showing that the activities elicited at beat frequency are correlated with individual differences in human behavior, specifically with accuracy in tapping the beat of rhythmic patterns and with individual temporal prediction abilities. Moreover, another experiment demonstrated that this rhythmic input-output transform is shaped by body movements. Enhanced neural activities were observed when listening to a rhythm subsequently to a body movement training session as compared to a listening session before. Most importantly, this boost was selective to frequencies corresponding to the rhythm to which the participants were trained to move. Together, these results indicate a link between rhythmic input-output transforms and beat representation, making this brain transform flexible and involving connections to motor brain areas. In collaboration with Pr. L. Maillard (CHU Nancy), we have recently implemented our approach to intracranial recordings performed in epileptic patients. This allowed us to demonstrate that beat perception involves a selective neural entrainment occurring already in the primary auditory cortex, and also in the premotor cortex.
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