Background: The deterioration of the central cholinergic system in aging is hypothesized to underlie declines in\r\nseveral cognitive domains, including memory and executive functions. However, there is surprisingly little direct\r\nevidence regarding acetylcholine�s specific role(s) in normal human cognitive aging.\r\nMethods: We used short-latency afferent inhibition (SAI) with transcranial magnetic stimulation (TMS) as a putative\r\nmarker of cholinergic activity in vivo in young (n = 24) and older adults (n = 31).\r\nResults: We found a significant age difference in SAI, concordant with other evidence of cholinergic decline in\r\nnormal aging. We also found clear age differences on several of the memory and one of the executive function\r\nmeasures. Individual differences in SAI levels predicted memory but not executive functions.\r\nConclusion: Individual differences in SAI levels were better predictors of memory than executive functions. We\r\ndiscuss cases in which the relations between SAI and cognition might be even stronger, and refer to other agerelated\r\nbiological changes that may interact with cholinergic activity in cognitive aging
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