Combining psychopharmacological and brain imaging approaches to study individual and social decision making in humans.

Summary The goal of this thesis was to study the brain mechanisms underlying social decision making in healthy subjects, the influence of gonadal steroid hormones on cognitive flexibility, and the brain dysfunctions underlying reward devaluation in Parkinson's disease. In our first protocol, we investigated how making a decision for oneself or for a group to which we belong, and when faced with a single individual or group, influences our inequity aversion and the brain regions engaged. Our results showed the influence of two distinct brain networks in inequity aversion during these social interactions, defining a brain signature for the "interpersonal/intergroup discontinuity" effect. Our second study aimed to determine the influence of hormone replacement therapy on cognitive flexibility in recently menopausal women. Numerous studies have shown a deleterious effect of hormone supplementation on cognitive functions if it is started late after menopause. However, a recent hypothesis has proposed that hormonal treatment may be beneficial and neuroprotective against psychiatric illnesses if started for a short time after the onset of menopause. In a study combining pharmacology and fMRI, we demonstrated modulation by hormone treatment on regions involved in cognitive control in recently menopausal women. Our latest study evaluates the effect of dopaminergic treatment and the presence of a specific impulse control disorder (i.e., hypersexuality) in patients with Parkinson's disease. Our preliminary results showed the influence of these factors on specific frontal and subcortical regions involved in choices, requiring the evaluation of different costs (i.e., effort/expectation) leading to greater or lesser rewards. Our thesis demonstrates the value of combining pharmacological and fMRI studies to understand how hormonal and dopaminergic treatments influence the brain mechanisms of individual and social decision.