Single-center Study of Gustation in Idiopathic Parkinson's Disease and Lewy Body Disease Using Gustatory Evoked Potential Analysis

The aim of the PI-PEG study is to explore the taste functions of the following 3 groups of participants: * healthy volunteers * patients with early Parkinson's disease * patients with incipient Lewy body disease. To this end, the results obtained from taste evoked potentials in each of the 3 groups of participants will be compared with each other and with different nutritional, motor and cognitive data. This study could reveal a difference in cortical processing of gustatory sensory information between patients who have had idiopathic Parkinson's disease progressing for 3 years or less, and patients who have had Lewy body disease progressing for 3 years or less. Indeed, a modification of taste evoked potentials (in terms of latencies) proportional to the degree of cerebral degeneration could be observed.

Inclusion Criteria: Healthy volunteers: * Person who has given written consent * Adult * Enrolled in the national register of healthy volunteers * Fasting \> 2 hours before PEG measurement * Body Mass Index (BMI) \< 30 kg/m². * No cognitive complaints and normal neurological assessment Patients with idiopathic Parkinson's disease: * Person who has given written consent * Adult * Fasting \> 2 hours before PEG measurement * Body Mass Index (BMI) \< 30 kg/m². * Diagnostic criteria for established or probable IPD Patients with Lewy body disease: * Person who has given written consent * Adult * Fasting \> 2 hours prior to PEG measurement * Body Mass Index (BMI) \< 30 kg/m². * Diagnostic criteria for probable or possible LBD Exclusion Criteria: * Non-affiliated to national health insurance * Person under legal protection (curatorship, guardianship) * Person subject to a court order * Pregnant, parturient or breast-feeding women * Major unable to give consent * MMSE score \< 15 and/or MoCA \< 10 * Known infection with COVID-19 in the 6 months prior to inclusion * Active smoker (\> 4 cigarettes per day on a regular basis) * Subject with pacemaker (contraindication for bioelectrical impedancemetry) * Diabetic (type 1 or type 2) * Taking medication (in progress at the time of the study) that interferes with gustation