Progressive neural engagement within the IFG-pMTG circuit as gesture and speech entropy and MI advances

Semantic representation emerges from distributed multisensory modalities, yet a comprehensive understanding of the functional changing pattern within convergence zones or hubs integrating multisensory semantic information remains elusive. In this study, employing information-theoretic metrics, we quantified gesture and speech information, alongside their interaction, utilizing entropy and mutual information (MI). Neural activities were assessed via interruption effects induced by High-Definition transcranial direct current stimulation (HD-tDCS). Additionally, chronometric double-pulse transcranial magnetic stimulation (TMS) and high-temporal event-related potentials were utilized to decipher dynamic neural changes resulting from various information contributors. Results showed gradual inhibition of both inferior frontal gyrus (IFG) and posterior middle temporal gyrus (pMTG) as degree of gesture-speech integration, indexed by MI, increased. Moreover, a time-sensitive and staged progression of neural engagement was observed, evidenced by distinct correlations between neural activity patterns and entropy measures of speech and gesture, as well as MI, across early sensory and lexico-semantic processing stages. These findings illuminate the gradual nature of neural activity during multisensory gesture-speech semantic processing, shaped by dynamic gesture constraints and speech encoding, thereby offering insights into the neural mechanisms underlying multisensory language processing.