Functional imaging studies of dopamine system and cognition in normal aging and Parkinson's disease

Modern functional imaging methods, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), provide non-invasive, quantitative tools for the direct measurement of neurotransmitter function in the living human brain. The dopamine system has been of key interest; first, because it has a prominant role in several cognitive and motor processes, and secondly because the tracers currently available for the dopamine system enable an effective investigation of various pre, post- and intra-synaptic processes. Recent functional imaging findings indicate that certain cognitive deficits associated with both normal aging and Parkinson's disease are modulated by changes in the brain dopamine system. This review covers the literature related to age-associated phenomena in the dopamine system studied with in vivo imaging. In particular, the focus is on describing and discussing the relationships between aging, cognition and the dopaminergic system in healthy subjects and in patients with Parkinson's disease.