Motor Activation in Multiple System Atrophy and Parkinson Disease: a Positron Emission Tomography (PET) Study

H215O PET investigations will be performed during two pharmacological conditions: OFF (e.g after 12 hours of usual dopaminergic treatment discontinuation) and ON (after an acute oral levodopa challenge) in all subjects. During each PET there will be two motor conditions: rest (no movement, hand and wrist lying on the joystick) and a right-hand movement, consisting of moving joystick in 4 four different directions avoiding sequence repetition performed at rest and during a right hand movement.

Levodopa: the dosage of levodopa challenge will be equivalent to the first morning dose increased by 100 mg of levodopa whereas the dosage will be 200 mg in healthy subjects.