Language usage shapes neural mechanisms of code-switching

Linguistic environments play an important role in shaping the mechanisms of language processing. The current study examined how neural responses to bilingual code-switching vary as a function of ongoing language usage, and which control processes may underlie these differences. Forty highly proficient English-French bilinguals listened to continuous spoken narratives containing inter-sentential switches. Participants were matched for proficiency and language background but differed in their current L2 usage (Active vs. Inactive). Narratives alternated either between their first and second languages, or between language and an acoustically matched non-linguistic signal, providing a means to probe language disengagement and re-engagement. While comprehension and cortical speech tracking were comparable across groups, oscillatory analyses revealed a usage-dependent modulation of alpha-band activity. Active bilinguals showed comparable alpha responses to switch and non-switch sentences, whereas Inactive bilinguals showed reduced alpha power following language switches, emerging from 650 ms over parieto-occipital regions. The direction, timing, and location of this effect are consistent with later attention control processes rather than early perceptual responses to the switch. Further analyses suggested that group differences were more closely associated with language disengagement than re-engagement. Together, these findings demonstrate an association between current L2 usage and alpha-band responses during language switching, suggesting that ongoing language experience may be modulating the neural mechanisms of language control.