"Reward processing plays a fundamental role in motivation, learning and cognition. Using fMRI in humans, we recently identified the neural structures involved when anticipating uncertain rewards. Cognitive impairments and dysfunction of the dopaminergic system are observed in healthy aging and in several neurological and psychiatric disorders. Moreover, damage from stroke and neurodegeneration in dementia may be retarded by estrogen and estrogens may prevent the deleterious effects of aging on cognition when administered soon after the cessation of ovarian function. However little is known about the effects of ageing and hormone replacement therapy (HRT) on the reward system and dopamine synthesis. The goals of this research program are to investigate the role of ageing in men and women and the effect of age-related hormonal decline in post-menopausal women with and without hormone replacement therapy on activation of the reward system and on dopaminergic. Using both fMRI and fDOPA PET, we shall investigate: 1) the activation of the reward system with fMRI in our monetary reward task; 2) dopamine synthesis in the midbrain and the striatum using F-DOPA PET; 3) the relationships between activation of the reward system and the levels of midbrain/striatum dopamine synthesis by combining fMRI and F-DOPA PET results in the same individuals; 4) the effect of HRT on the reward system and the dopaminergic function in post-menopausal women. Our findings should clarify the relationships between activation of the reward system, dopamine synthesis and the effect of ageing and HRT."