All baseline characteristics in MSA, PD and healthy volunteers will be compared by the Man-Whitney U test. For PET imaging, the 36 subjects will be included in the same statistical analysis on a voxel-by-voxel basis. Statistical parametric maps will be generated using an ANCOVA model implemented through the General Linear Model formulation of SPM after normalization for global effect by proportional scaling. We will analyze three main effects 1) The "movement effect" consists of comparing the images obtained during hand movement with those acquired at rest for each group (MSA, PD and Healthy subjects) using the Family Wise Error (FWE) statistical threshold at P < 0.05 for peak height in OFF and ON conditions. 2) Difference between motor activation of the three groups in OFF condition. 3) Difference between motor activation during OFF and ON condition in each group reflecting levodopa effect on motor activation. For inter groups comparisons statistical threshold will set at p<0.01 with clusters>10 voxels.