 Patients et method: PD patients waiting for STN-DBS, will be assessed in a preoperative time 2 times at, at least, 3 month intervals, to evaluate the natural history of the disease on upper gastrointestinal symptoms and motility and in a postoperative time, after 6 months of chronic STN-DBS. Each assessment will include : 1 questionnaires about frequency and severity of upper gastrointestinal symptoms; 2 a nutritional assessment body mass index, dietary assessment; 3 the gastric emptying measurement with the 13C-octanoic acid breath test; 4 the colorectal transit time measurement with radio-opaque markers 5 an indirect calorimetry to estimate resting energy expenditure; 6 and plasmatic leptin and ghrelin concentrations, hormones involved in the homeostatic regulation of appetite. 