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Abstract

Theta band oscillations are known to underlie both language comprehension and domain-general cognitive abilities. It remains an open question whether it is one and the same theta oscillation underlying those functions. Here we show that theaging brain can provide an answer, thereby resolving a long-standing paradox. While resting state (RS) theta power declines with age, low RS theta power predicts better cognitive functioning but sentence comprehension does not improve with old age but deteriorates instead. We resolve this paradox showing that sentence comprehension declines due to changes in RS theta power within domain-general brain networks known to support successful sentence comprehension, while low RS theta power within the left-hemispheric dorso-frontal language network predicts intact sentence comprehension. The two RS theta networks were also found to functionally decouple relative to their independent internal coupling. Thus, both temporally and spatially distinct RS theta oscillations differentially predict the preservation of the core sentence processing network across the lifespan as well as the age-related decline in sentence comprehension due to underlying changes in domain-general brain networks.