NORMAL AND PATHOLOGICAL AGING - FINDINGS OF POSITRON-EMISSION-TOMOGRAPHY

Normal aging of the brain is predominantly characterized by metabolic changes in the prefrontal cortex. While in middle age there is a trend to hyperfrontality, PET demonstrates in old age a decline of regional cerebral glucose metabolism in frontal areas. In progeric diseases, c linically apparent as premature aging, the metabolic pattern is simila r like in normal aging but qualitatively more severe. In patients with the diagnosis of probable Alzheimer's disease (AD) hypometabolism in early dementia is typically present in heteromodal association areas. Hypometabolism then spreads to other cortical and subcortical regions suggesting a characteristic pattern of degeneration that reflects sele ctive vulnerability within limbic-cortical networks. Synaptic plastici ty, clinically apparent as cognitive reserve capacity, can be assessed by PET under specific cognitive activation. In AD it is reduced in co mparison to age-matched normals and may be influenced by drugs giving trophic support to neurochemical systems.