Novel word learning in older adults: A role for sleep?

Abstract

Sleep is an offline period during which newly acquired semantic information is transformed into longer-lasting memories. Language acquisition, which requires new word learning and semantic integration, is preferentially benefitted by a period of sleep in children and young adults. Specific features of sleep (e.g., sleep stage characteristics) have been associated with enhanced language acquisition and generalization. However, with increasing age, even in healthy individuals, sleep quality and quantity decrease. Simultaneously, deficits in word retrieval and new word learning emerge. Yet it is unknown whether age-related alterations in language ability are linked with alterations in sleep. The goal of this review is to examine changes in language learning and sleep across the lifespan. We consider how sleep detriments that occur with aging could affect abilities to learn novel words and semantic generalization and propose hypotheses to motivate future research in this area.

Keywords: Consolidation; Language; Lexicon; Sleep; Spindles; Word learning.

Figure 1

A model for how sleep-dependent processes facilitate language learning. Slow Wave Sleep is necessary for strengthening and stabilization of newly learned words, contributing to veridical recall. Sleep spindles are indicative of thalamocortical and hippocampocortical interaction, thus possibly fostering the integration of newly learned words into the existing lexicon.

Figure 2

Age-related differences in lexical integration components. WM = working memory; V = vocabulary. Older adults may overcome working-memory deficits by drawing upon their existing vocabulary to achieve lexical integration as well as young adults.

Figure 3

Typical nocturnal hypnograms demonstrating sleep stage proportion and distribution for a young and older adult. Relative to young adults, older adults have less SWS, more nREM2 sleep, and sleep stages are more fragmented. Differences in sleep architecture may hinder sleep-dependent lexical integration in older adults.