Hippocampal plasticity in normal aging and decreased plasticity in Alzheimer's disease.

Different patterns of age-related dendritic change have been reported in different zones of the human hippocampal region in the normal and Alzheimer's disease (AD) brain. In normal aging there is an increase in average (net) dendritic extent (which we interpret as plasticity) in the parahippocampal gyrus and dentate gyrus. There is net stability of dendritic extent in CA2-3, CA1, and subiculum. In regions that show plasticity in normal aging, dendrites in AD show reduced or aberrant plasticity. In regions that show stability in normal aging, dendrites either are stable or regress in AD, depending upon how severely involved the region is with the pathology of AD.