Mu rhythm motor-auditory delay in imagined speech mirrors overt speech timing.

Speaking-whether overtly or covertly-requires a mapping between motor commands and their sensory consequences, a process of sensorimotor coordination. The timing of sensorimotor coordination during overt speech is relatively well established. Here we asked whether during imagined speech sensorimotor coordination can preserve this timing and remain grounded in the same biophysical constraints underlying vocal articulation. We instructed participants to imagine producing visually presented syllables (/pa/, /ta/, /ka/). Using magnetoencephalography (MEG), we investigated the spatiotemporal dynamics of mu rhythm (8-30 Hz) power suppression. Cluster-based permutation analysis reveals a segregation of alpha (8-12 Hz) and beta (15-30 Hz) frequencies to auditory and motor areas, respectively. Latency analyses show that beta suppression in motor areas precedes alpha suppression in auditory areas by ~ 120 ms. This delay closely matches sensorimotor coordination time windows previously reported for overt speech. While prior work provided only indirect evidence for the temporal equivalence between imagined and overt speech-by probing the system with altered auditory feedback-our findings offer direct evidence by measuring strictly internal neural processes. Together, the results demonstrate the suitability of alpha-beta power suppression as a neural marker that separately indexes motor and auditory processes associated with imagined speech production.