This study will investigate whether seven days administration of the serotonin receptor subtype 4 (5-HT4) partial agonist prucalopride has effects on emotional processing and neural activity in healthy volunteers, compared to placebo administration. Using an experimental medicine approach, the effects of prucalopride on cognitive biomarkers of antidepressant action will be characterised. In a double-blind design, participants will be randomised to receive seven days administration of either prucalopride (1mg daily) or placebo. All participants will come for a Screening visit, Research Visit One (including an MRI scan) and Research Visit Two (including measures of emotional processing and non-emotional cognition). The primary study hypothesis is that seven-day prucalopride administration will have positive effects on emotional processing and reward sensitivity. A secondary hypothesis is that seven-day prucalopride administration will alter non-emotional cognition. Finally, the study will test the hypothesis that seven day prucalopride administration will alter neural activity during an emotional faces task and a memory task.

Inclusion Criteria:

• Participant is willing and able to give informed consent for participation in the study
• Male or female
• Aged 18-40 years
• Sufficiently fluent English to understand and complete the task
• Right handed
• Body Mass Index in the range of 18-30
• Not currently taking any medications (except the contraceptive pill)

Exclusion Criteria:

• Not fluent in English
• Any past or current Axis 1 DSM-V psychiatric disorder
• Current usage of psychoactive medication (except the contraceptive pill, the Depo-Provera injection or the progesterone implant)
• Current usage of any medication that will influence the MRI scan
• Current or past history of drug or alcohol dependency
• Currently pregnant or breastfeeding
• Study visits due to take place during the pre-menstrual week (female participants asked details of their menstrual cycle to schedule the study outside this week)
• Not right handed
• Body Mass Index outside the range of 18-30
• History of cardiac, thyroid, or liver problems
• An autoimmune disorder
• Current, or a history of, gastro-intestinal disorder or irritable bowel syndrome
• Epilepsy
• Known lactate deficiency or any other problem absorbing lactose, galactose, or glucose
• Participation in a study which uses the same computer tasks as those used in the present study
• Participation in a study that involves the use of a medication within the last three months
• Smoker > 5 cigarettes per day
• Typically drinks > 6 caffeinated drinks per day
• Any contraindication to MRI scanning (e.g. metal objects in the body, pacemakers, significant claustrophobia)