CT CHANGES ASSOCIATED WITH NORMAL AGING OF THE HUMAN BRAIN

CT was used to measure changes in cerebral gray and white matter tissu e densities associated with normal aging, using a cross-sectional desi gn, in order to provide normative data for comparisons with abnormal a ging such as dementias of Alzheimer's and vascular types. Cerebral com partmental densities were measured using plain CT; and their perfusion values were recorded during stable xenon inhalation (CT-CBF), among 8 1 neurologically and cognitively normal volunteers of different ages. Results led to the conclusion that cortical gray matter tissue densiti es progressively decline (polio-araiosis) after age 60. Cortical polio -araiosis is coupled with regional hypoperfusion but not with cortical atrophy. It is speculated that the cortical hypodensity identified by CT imaging parallels declines in cortical synaptic density, as report ed from autopsy studies using anti-synaptophysin staining of cerebral cortex obtained from normal people above and below age 60. The couplin g of cortical hypoperfusion with polio-araiosis is believed to reflect age-related reductions of cortical metabolic demands as reported by P ET. During normal aging leuko-araiosis correlates directly with cortic al atrophy, suggesting that anterograde axonal degeneration resulting from cortical neuronal dearborization play a role in its causation.