Beyond fixed beats: adaptive musical entrainment for precision neurorehabilitation in neurodegenerative disorders.

Music-based interventions have become a promising avenue for neurorehabilitation in neurodegenerative disorders, particularly through rhythmic auditory stimulation to improve gait and movement timing. However, many current interventions still rely on pre-specified or externally imposed rhythmic structures, treating music primarily as a cue to be followed. In this Opinion article, I argue that the next generation of music-based neurorehabilitation should move beyond fixed beats or individualized cueing protocols toward real-time adaptive musical entrainment. Two biologically grounded principles are central to this shift. First, healthy movement is not metronomic: gait exhibits structured variability, including long-range correlations and 1/f-like temporal organization, which can be disrupted in neurodegenerative disease. Because music can contain 'pink,' multiscale temporal structure in specific acoustic or rhythmic time series, it offers a promising medium for adaptive cue design and for testing whether structured auditory variability can support more functional movement organization. Second, adaptive music should be understood not merely as tempo matching, but as adaptive auditory-motor timing control in which phase synchronization is one important dimension, among others. Closed-loop musical technologies can continuously sense movement, adapt musical parameters, and support stable yet flexible coupling between body and sound. Because the empirical foundation for music-based gait rehabilitation is currently strongest in Parkinson's disease, this article uses PD gait as the primary model while treating extension to atypical parkinsonian syndromes and other neurodegenerative disorders as a translational hypothesis requiring disease-specific validation. I propose that precision neurorehabilitation may integrate individual movement signatures, structured temporal variability, and phase-based adaptive cueing to guide the development of interventions that are more personalized, engaging, and ecologically grounded. Music, in this framework, does not simply tell the patient when to move; it listens back and adapts to support more functional movement dynamics.