Evaluating the temporal order of motor and auditory systems in speech production using intracranial EEG.

Theories propose that speech production can be approximated as a temporal reversal of speech perception. For example, phonological code is assumed to precede phonetic encoding in the motor system during speech production. However, empirical neural evidence directly testing the temporal order hypothesis remains scarce, mostly because of motor artifacts in non-invasive electrophysiology recordings and the requirements of both temporal and spatial precision. In this study, we investigated the neural dynamics of speech production using stereotactic electroencephalography (sEEG). In both onset latency analysis and representational similarity analysis (RSA), activation in the auditory region of the posterior superior temporal gyrus (pSTG) was observed before articulation, suggesting the availability of auditory phonological code before production. Surprisingly, the activation in the motor region of the inferior frontal gyrus (IFG) preceded that of pSTG, suggesting that the phonological code in the auditory domain may not necessarily be activated before the encoding in the motor domain during speech production.