Practice effect and beyond: reaction to novelty as an independent predictor of cognitive decline among older adults.

Practice Effects (PE) have been gaining interest as an early marker of pathological cognitive decline among older adults, with cognitively compromised individuals exhibiting diminished or absent PE, presumably due to reduced ability to learn. However, the opposite pattern has also been observed, with MCI participants showing larger PEs than controls. In this prospective cohort study, we examined the possibility that individuals with incipient cognitive decline may be more "thrown" by task novelty, which may inflate PE due to diminished performance during the first exposure to the task. We assessed Novelty Effect (NE) and Learning (LRN) on a motor task in 50 community-dwelling independent older adults who expressed a concern about their cognition. Results showed that larger NE was associated with greater cognitive decline 17 months later, reliably classifying participants into decliners and nondecliners. LRN did not independently explain any variance in future cognitive change, but moderated the relationship between NE and decline and correlated with the level of cognition at baseline and follow-up. These findings highlight the differing contributions of NE and LRN to PE, and demonstrate that NE may be sensitive to depletion of cognitive reserve among individuals who are on the verge of exhibiting a reliable cognitive decline.