The source of the associative deficit in aging: the role of attentional resources for processing relational information

Previous studies have proposed an associative deficit hypothesis, which attributes part of older adults' deficient episodic memory performance to their difficulty in creating cohesive episodes. According to the ADH, older adults show disproportionate deficits in relational memory (RM) relative to item memory (IM). The disproportionate RM deficit in older adults has been demonstrated with a variety of memory tasks, such as word-word, word-font, and face-name pairs. Despite rich evidence of an age-related RM deficit, the source of this deficit remains unspecified. One of the most widely investigated factors is the reduction in attentional resources in older adults. To investigate the effect of reduced attentional resources on RM performance, previous researchers have imposed a secondary task load on young adults during encoding of memory lists to divide attentional resources into two different tasks. However, none of the existing studies have found a disproportionate RM impairment in young adults under divided attention conditions. The current project investigated whether a reduction in attentional resources for relational processing underlies the memory impairments observed in aging. Using behavioral and functional neuroimaging techniques, I conducted three studies aimed at determining: 1) whether imposing a secondary task load for relational processing makes young adults' memory performance mimic the age-related RM deficit, and 2) whether the effect of reduced attentional resources for relational processing on RM is similar to the effect of aging at the neural level, using functional magnetic resonance imaging (fMRI). The results from the two behavioral studies indicate that a reduction in attentional resources for relational processing in young adults during encoding equates their performance in RM to that of older adults. Furthermore, the results from the fMRI study demonstrate that both aging and reductions in relational attention processing in young adults significantly reduced activity in the brain areas critical for RM formation, namely, the ventrolateral and dorsolateral PFC, superior and inferior parietal regions, and left hippocampus. This converging evidence from behavioral and neuroimaging studies thus documents the first evidence that the reduction in attentional resources for relational processing is the critical factor for the age-related RM deficit