Adaptation and anticipation mechanisms under unpredictable auditory perturbations: the role of perturbation type, stimulus complexity and cerebellar impairment

Introduction: Aligning movements with external rhythms depends on temporal adaptation and anticipation, jointly captured by the ADaptation and Anticipation Model (ADAM). Cerebellar pathology disrupts these mechanisms during gradual tempo changes, but its role in synchronization under unpredictable rhythmic structure remains unclear. Methods: Sixty-one participants (16 cerebellar, 45 controls) performed a finger-tapping task at 100 beats-per-minute with phase-shifts (±90°) or period-changes (±10%). Synchronization was assessed by quantifying asynchrony (mean, variability) and modeled with ADAM to estimate adaptation (phase, period correction), anticipation (temporal prediction, anticipatory error correction), and noise (timekeeper, motor). Mixed-effects ANOVAs assessed effects of group, stimulus, and perturbation type; regressions identified predictors of synchronization variability. Results: Patients showed higher asynchrony variability. Both groups increased phase and period correction from baseline to perturbation (p < 0.001), with stronger changes for period than phase perturbations (p < 0.006). Controls corrected more to metronomes, yet patients engaged period correction for music (p = 0.009). Temporal prediction relied on weighed averaging of preceding intervals under perturbations (p = 0.008), more with music, and particularly in patients (p = 0.0095). Anticipatory error correction was higher for metronomes than music (p = 0.045) and for period-changes (p < 0.0001), with stimulus effects restricted to controls. Timekeeper and motor noise rose with perturbations (p < 0.0001) and strongly predicted synchronization variability. Conclusion: Period-changes engaged adaptation more than phase-shifts, and music elicited larger corrective responses than metronomes. Patients showed reduced phase correction for metronomes, greater reliance on period correction for music, and elevated timekeeper noise. Findings indicate that the cerebellum contributes to multiple components of adaptation and anticipation, offering insights for designing targeted rehabilitation.