Sleep benefit (SB) is a prominent spontaneous, apparently unpredictable, transitory improvement in motor function reported by around 50% of patients affected by Parkinson's Disease (PD) after sleep and before taking their first dose of dopaminergic medications. The aim of this study is to test the hypothesis that objective and/or subjective improvement of motor function might be due to a carry-over effect of Rapid Eye Movements (REM) sleep at awakening from this sleep phase.