Jiachen Yao | The Long-Range Neural Interactions in Human Sentence Comprehension: Linking Structural and Functional Connectivities

The investigation of the dynamic neural interactions in the course of verbal working memory maintenance and speech comprehension has gained notable attention. A key question is how the brain processes different information (like words' meaning, syntax, etc.) from continuous speech and links them together to form hierarchical structures representing temporal events. Recent research on neural oscillations, crucial for cognitive functions, sheds light on this intricate process. We propose that both semantic meaning and syntactic labels of words in speech can be encoded via sparse bursts of multiple neural assemblies ("word-webs"). These word representations are maintained in working memory using the theta-gamma code, where each assembly emits a burst per theta-cycle. Successive word representations are then activated and retained in working memory via phase-shifted gamma bursts modulated at theta frequency. To merge individual words into larger linguistic units, like phrases or event structures, we suggest synchronization of gamma bursts, likely involving regions like the left inferior frontal gyrus (LIFG) and tempo-parietal areas associated with verbal working memory. Structural connectivity between these brain regions may modulate this merging process. Using MEG, we aim to investigate how theta-gamma interactions and long-range fronto-temporal synchronization support word maintenance and merging during auditory language comprehension. Additionally, we will fMRI sessions for a subset of subjects to localize the neural networks involved, aiding MEG source-level analysis. Diffusion-weighted imaging (DWI) data will be collected to assess individual structural connectivity. Finally, we will examine whether individual functional connectivity can be influenced by structural connectivity in the context of working memory maintenance and linguistic merging.