The multimodal stimulation probe will be positioned through the mouth in the distal esophagus. After the probe is positioned in the esophagus (top of the balloon 10 cm above the LES), it will be fixed to the chin and the volunteer will remain in a bed, in semi-recumbent position for the entire study period. Fifteen minutes after the ingestion of the multimodal esophageal stimulation probe, 10mg of chlorpromazine (Largactil®) or placebo (saline) will be slowly administered via intravenous injection. After de administration of chlorpromazine or placebo (saline) the multimodal stimulation tests will be initiated.