Resting state theta power as marker of successful language comprehension across the lifespan

Successful encoding of verbal information is a prerequisite for successful language comprehension, in both young and older adults. While language comprehension is often thought to remain rather stable across age, memory is known to decline. In the current study on young and older adults, this apparent paradox was addressed by combining a memory-intensive language-comprehension task with resting-state EEG as an electrophysiological indicator of both cognitive functioning and age-related cognitive decline. Whereas one line of research has shown decreased resting-state theta power to predict good general cognitive abilities, other studies showed that oscillatory power decreases with age across frequency bands, which coincides with age-related cognitive decline. We directly compared resting-state theta power linked to language performance in 19 young (mean age: 24) and 19 older adults (mean age: 65). As age-related effects, we predicted that, first, theta power decreases with age and that, second, language comprehension under high memory demands also decreases with age. Third, we predicted resting-state theta power to negatively correlate with language performance. The data revealed both decreased theta power and decreased language performance for older as compared to young adults. As a general effect, we found that across age groups, decreased theta power predicted higher language performance. Further analyses showed that the brain regions for which decreased resting-state theta power predicted successful language performance resembled that of the fronto-temporal language network. In sum, we show that decreased resting-state theta power is an electrophysiological indicator of both cognitive decline and good language performance. In other words: While decreased resting-state theta power indicates good language performance, language performance suffers when theta drops further during aging