Exploratory Study of the Expression of the Serotonergic 5-HT4 Receptor in Parkinson's Disease

Inclusion Criteria: * Man or woman : Age between ≥ 50 and ≤ 85 years old * For women: postmenopausal * Affiliated to a social security scheme or similar; * Having given written consent to participate in the free and informed study. * Level of study: ≥ 6 years of schooling * only for healthy volunteer : No history of neurological or psychiatric disease * Only for patient : Having a clinically established or probable diagnosis of Parkinson's disease according to the criteria defined by the Movement Disorder Society at a Hoehn and Yahr stage ≤ 3 (in on dopa conditions) and a duration of evolution of the disease between 2 and 8 years. * Only for patient : Having a MoCA (Montreal Cognitive Assessment) ≥ 20/30. Exclusion Criteria: * Diagnosis other than Parkinson's disease ( for patient only) * Treated with specific serotonin inhibitors (SSRIs), specific noradrenaline inhibitors (SNRIs), tricyclic antidepressants, monoamine oxidase inhibitors (MAOIs) and neuroleptics in the last 3 months * Use of recreational drugs interfering with the serotonergic system (ecstasy, MDMA) or opioids (cannabis, opiates) in the last 3 months or chronic use * Contraindication to magnetic resonance imaging (MRI) or positron emission tomography (PET) * Participation in the last year to a study using ionizing radiation or concomitant participation in another research project involving the human being that may interfere with the results or the conclusions of this study * Exceeding the annual amount of compensation authorized for participation in research protocols * Deprivation of liberty by judicial or administrative decision, person subject to a legal protection measure * BMI ≥ 35kg/m2 * Presence of depression (BDI-2 score ≥21), anxiety (Parkinson Anxiety Scale (PAS) score ≥14) or apathy (STARKSTEIN score ≥14) - (for healthy volunteers only) * Cognitive impairment (MOCA score ≤26) (for healthy volunteers only) * Current or past neurological or psychiatric pathology (for healthy volunteers only) * Serious and progressive medical pathology * Current or past dependence on any addictive substance according to DSM-V (The Diagnostic and Statistical Manual of Mental Disorders) criteria (alcohol, cannabis, hallucinogens, inhalants, opiates, sedatives, stimulants), except tobacco and caffeine. (for healthy volunteers only)