Quantitative changes in some subcortical nuclei in aging, Alzheimer's disease and Parkinson's disease.

In normal aging, AD/SDAT and Parkinson's disease, the changes in subcortical neuronal systems are similar in quality and distribution, but highly variable in their intensity. Some correlations between the intensity and pattern of lesions in some subcortical nuclei with changes in cortical target areas in AD/SDAT suggest that age-related subcortical changes may represent a secondary phenomenon (antograde or retrograde degeneration) due to primary cortical damage. However, severe depletion of subcortical nuclei in both AD/SDAT and PD may also occur without considerable cortical pathology which is more compatible with a concomitant degeneration of both subcortical and intracortical neuronal systems.