Rapid Eye Movement Sleep Homeostatic Response: A Potential Marker for Early Detection of Parkinson's Disease.

Parkinson’s disease (PD) is a long-term neurodegenerative disease characterized by the presence of dopaminergic neuronal loss and dysfunction in the substantia nigra. Motor disturbance is the symptom most typically reported, including bradykinesia plus either limb rigidity, resting tremor, or postural instability [1–3]. Importantly, it has been reported that at the point when the patient meets criteria for the principal of motor disturbance, approximately 60% of substantia nigra neurons are lost [4]. Non-motor symptoms have also been observed in both PD patients as well as in related animal models, including pain, autonomic dysfunction, depression, anxiety, olfactory dysfunction, cognitive impairment and sleep disorders [5,6]. The presence and severity of these non-motor symptoms as the disease progresses exacerbate the degree of disability of PD patients. These non-motor symptoms suggest that neurodegenerative processes in PD extends beyond the substantia nigra and dopaminergic deficit [6–10]. It has been noted that before PD becomes clinically significant, neurodegeneration has been ongoing for some time. This has led to the notion of a “pre-motor” phase [11], during which non-motor manifestations and a variety of other abnormalities may offer key biomarkers of the disease process.