Age-related changes in sleep-dependent novel word consolidation

Learning new words is a vital, life-long process that benefits from memory consolidation during sleep in young adults. In aging populations, promoting vocabulary learning is an attractive strategy to improve quality of life and workplace longevity by improving the integration of new technology and the associated terminology. Decreases in sleep quality and quantity with aging may diminish sleep-dependent memory consolidation for word learning. Alternatively, given that older adults outperform young adults on vocabulary-based tasks, and that strength of memory encoding (how well older adults learn) predicts sleep-dependent memory consolidation, word learning may uniquely benefit from sleep in older adults. We assessed age-related changes in memory for novel English word-definition pairs recalled following intervals spent asleep and awake. While sleep was shown to fully preserve memory for word/definition pairs in young adults (N = 53, asleep = 32, awake = 21, 18-30 years), older adults (N = 45, asleep = 21, awake = 24, 58-75 years) forgot items equally over wake and sleep intervals but preserved the accuracy of typed responses better following sleep. However, this was modulated by the strength of encoded memories: the proportion of high strength items consolidated increased for older adults following sleep compared to wake. Older adults consolidated a lower proportion of medium strength items across both sleep and wake intervals compared to young adults. Our results contribute to growing evidence that encoding strength is crucially important to understand the expression of sleep-dependent benefits in older adults and assert the need for sufficiently sensitive performance metrics in aging research.