Aging
Normal aging is associated with hippocampal atrophy and declines in white matter integrity. Whereas age related changes in hippocampal volume lead to selective reductions in episodic memory, declines in white matter integrity as indexed by white matter hyperintensities are associated with reductions in both episodic memory and working memory.
In addition, white matter declines in aging lead to reductions in prefrontal activity during episodic retrieval and working memory tasks. These results suggest that disruption of white matter tracts, particularly in the prefrontal cortex, may be a mechanism for age related declines in memory.
Despite various brain changes related to aging, some forms of memory are well preserved in old age. For example, perceptual implicit memory (i.e., fragment completion) and conceptual implicit memory (i.e., exemplar generation) are well preserved in the aged. In contrast, however, abnormal aging associated with Alzheimer’s Disease is associated with reductions in conceptual implicit memory.