Impairment in associative memory in healthy aging is distinct from that in other types of episodic memory

There is evidence that age related changes in episodic memory are heterogeneous and result from diverse pathologies. To test this, we examined performance of healthy high-functioning younger (N = 41, ages 18-60 y) and older (N = 58, ages 61-83 y) individuals in tests of associative memory, logical memory and memory in executive and object-recognition domains. We compared their relationships to each other and to other cognitive functions, including, psychomotor speed and verbal and spatial working memory. Older individuals showed significantly greater reduction in an index of the ability to learn new associations (NAL) than for memory in executive and object-recognition domains. Age-related reduction in NAL and in logical memory was of similar severity, but the two measures showed only moderate correlation when age and other cognitive functions were controlled for. NAL shows an age-related pattern of change distinct from memory in executive and object-recognition domains and from logical (item) memory. We propose that in healthy well-functioning individuals, NAL taps processes which support binding of newly learned association in context of accumulating information, a key function of the hippocampus. NAL may thus serve as a selective marker of complex, hippocampus-based, cognitive functions in studies of normal cognitive aging and of its possible relationship to early dementia. (C) 2012 Elsevier Ireland Ltd. All rights reserved.