Alpha and beta oscillations differentially support word production in a rule-switching task

Abstract

Research into the role of brain oscillations in basic perceptual and cognitive functions has suggested the alpha rhythm reflects functional inhibition while the beta rhythm reflects neural ensemble (re)activation. However, little is known regarding the generalization of these proposed fundamental operations to linguistic processes, such as speech comprehension and production. Here, we recorded magnetoencephalography (MEG) in participants performing a novel rule-switching paradigm. Specifically, Dutch native speakers had to produce an alternative exemplar from the same category or a feature of a given target word embedded in spoken sentences (e.g., for the word tuna an exemplar from the same category—seafood—would be shrimp, and a feature would be pink). A cue indicated the task rule—exemplar or feature—either before (pre-cue) or after (retro-cue) listening to the sentence. Alpha power during the working-memory delay was lower for retro-cue compared to pre-cue in left hemispheric language-related regions. Critically, alpha power negatively correlated with reaction times, suggestive of alpha facilitating task performance by regulating inhibition in regions linked to lexical retrieval. Furthermore, we observed a different spatiotemporal pattern of beta activity for exemplars vs. features in right temporo-parietal regions, in line with the proposed role of beta in recruiting neural networks for the encoding of distinct categories. Overall, our study provides evidence for the generalizability of the role of alpha and beta oscillations from perceptual to more complex (linguistic) processes, and offers a novel task to investigate links between rule-switching, working memory, and word production.

Significance Statement It remains unclear whether the proposed functional role of alpha and beta oscillations in perceptual function is generalizable to higher-level cognitive processes. We constructed a novel rule-switching paradigm involving speech comprehension and word production. We found that alpha power is modulated by cognitive load and is linked to task performance, potentially by regulating inhibition in brain regions linked to lexical retrieval. Additionally, the spatiotemporal pattern of beta activity differed between two distinct task rules, in line with the proposed role of beta in encoding of distinct categories and recruitment of respective neural networks. We offer experimental findings that support the view of a domain-general role of oscillations across the hierarchy of cognitive functions, from low-level sensory operations to high-level processes.