Naturalistic language comprehension is supported by alpha and beta oscillations linked to domain-general inhibition and reactivation

Abstract

Brain oscillations are prevalent in all species and are involved in numerous perceptual operations. Alpha oscillations are thought to facilitate processing through the inhibition of task-irrelevant networks, while beta oscillations are linked to the reactivation of content representations. Can the proposed functional role of alpha and beta oscillations be generalized from low-level operations to higher-level cognitive processes? Here we address this question focusing on naturalistic spoken language processing. Twenty-two (18 female) Dutch native speakers listened to stories in spoken Dutch and French while magnetoencephalography (MEG) was recorded. We used dependency parsing to identify three dependency states at each word, as the number of (1) newly opened dependencies, (2) dependencies that remained open, and (3) resolved dependencies. We then constructed linear forward models to predict alpha and beta power from the dependency features. Results showed that dependency features predict alpha and beta power in language-related regions beyond low-level linguistic features. Left temporal, fundamental language regions are involved in language comprehension in the alpha band, while frontal and parietal, higher-order language regions, and motor regions are mostly involved in the beta band. Critically, alpha and beta band dynamics seem to subserve language comprehension tapping into syntactic structure building and semantic composition by providing low-level mechanistic operations for inhibition and reactivation processes. Overall, this study sheds light on the role of alpha and beta oscillations during naturalistic language processing, providing evidence for the generalizability of these dynamics from perceptual to complex linguistic processes. Significance StatementPrior research identified the functional role of alpha and beta oscillations in basic perceptual and motor functions. However, it remains unclear whether their proposed role can be generalized to higher-level processes during language comprehension. Here, we found that high-level syntactic features predict alpha and beta power in language-related regions beyond low-level linguistic features when listening to comprehensible naturalistic speech. Our work contributes to the debate about whether the functional roles of brain oscillations are domain-general or depend on the task at hand. We offer experimental findings that integrate a neuroscientific framework on the role of brain oscillations as "building blocks" with language comprehension as a compositional process, and novel evidence regarding the encoding of higher-level syntactic operations in the brain. This supports the view of a domain-general role of cortical oscillations across the hierarchy of cognitive functions, from low-level sensory operations to complex linguistic processes.