Testing the role of beta band and the Inferior Frontal Gyrus in linguistic prediction with HD-tACS

Introduction: Language comprehension is thought to rely on the pre-activation of linguistic representations based on context, facilitating the processing of upcoming input. Prediction-by-production models propose that linguistic prediction draws on processes and representations shared with language production. To test this proposal, we applied high-density transcranial alternate current stimulation (HD-tACS) targeting a specific brain oscillatory band and a brain region known to be involved in language production, namely the beta band (13-30 Hz) and the left inferior frontal gyrus (lIFG). Methods: Participants performed a lexical decision task in which target words were either predictable or non-predictable based on sentence context, across two separate sessions. In one session, participants received active tACS at 20 Hz; in the other session, they received sham stimulation. In the first study (N = 19), stimulation was applied during task performance; in the second study (N = 18) the stimulation was administered prior to the task (20 min, 1.25 mA intensity). Results: Across both studies, we did not observe stimulation effects on lexical decision response times. Conclusion: Our findings do not support the involvement of beta-band activity within the lIFG in predictive processes. However, null results should be interpreted with caution: improvements in stimulation parameters (intensity, duration, number of repetitions, use of individualized peak frequencies) may yield more robust effects.