Whitford, Thomas J.Spencer, Kevin M.Godwin, MariantheHirano, YojiChung, Lawrence Kin HeiVodovozov, WadimGriffiths, OrenHarris, Anthony W.F.Le Pelley, Mike E.Jack, Bradley N.2026-09-162026-09-16PubMed:39843220https://hdl.handle.net/1885/733815476Inner speech refers to the silent production of language in one’s mind. As a purely mental action without obvious physical manifestations, inner speech has been notoriously difficult to quantify. To address this issue, the present study repurposed the phenomenon of speaking-induced suppression, wherein overt speech has been consistently shown to elicit reduced auditory evoked potentials compared with externally generated speech, as well as changes in oscillatory activity in gamma and theta frequency bands. Given the functional similarities between inner and overt speech, we used an established experimental protocol to investigate whether similar metrics could be used to distinguish the content of inner speech. Healthy participants (n = 129) produced an inner syllable at a precisely specified time. An audible syllable was concurrently presented which either matched or mismatched the content of the inner syllable. The results revealed that Match and Mismatch conditions could be differentiated on the basis of their evoked oscillations in the gamma, theta, and alpha bands. Notably, there was a gamma-band oscillation in the vicinity of the P2 that differed between the Match and Mismatch conditions, suggesting that “late” gamma-band activity may index consciously perceived expectancy violations, or cognitive prediction errors. Regarding the auditory evoked potentials, the N1 component was suppressed in the Match condition while the P2 component was suppressed in the Mismatch condition, replicating previous findings. This study provides support for the existence of “inner speaking-induced suppression”, and demonstrates that inner syllables can be differentiated based on their influence on the electroencephalographic activity elicited by simulta-neously-presented audible syllables.This work was supported by the Australian Research Council (DP200103288, DE220100739) and the National Health and Medical Research Council of Australia (APP2004067).13enPublisher Copyright: © 2025 Whitford et al.auditory evoked potentialEEGgammainner speechN1prediction error202510.1523/ENEURO.0297-24.202585218415069