Motor–Behavioral Phenotypes in the RBD-PD Continuum: Neurophysiological Mechanisms and Rehabilitative Implications

REM sleep behavior disorder (RBD) represents a prodromal manifestation of Parkinson’s disease (PD), reflecting the breakdown of inhibitory networks extending from the brainstem to the cortex. This review synthesizes pathological, physiological, and behavioral evidence to illustrate how early α-synuclein pathology disrupts REM-sleep atonia and motor automaticity through degeneration of pontomedullary and cholinergic–inhibitory circuits. The resulting failure of inhibitory precision links nocturnal REM sleep without atonia to daytime gait and postural abnormalities, framing RBD as a dynamic systems disorder rather than a purely sleep-related phenomenon. By examining this continuum across neurophysiological, behavioral, and clinical domains, the review highlights current knowledge gaps, particularly regarding the temporal dynamics of degeneration and compensation. It further integrates multimodal biomarkers that capture these transitions in vivo and discusses therapeutic strategies aimed at preserving inhibitory network integrity and delaying phenoconversion to overt Parkinsonian syndromes.