Probing the role of left inferior frontal gyrus in vocal motor control: Evidence from TMS and causal inference analysis

Beyond an established role in speech initiation and planning, the left inferior frontal gyrus (IFG) may contribute to sensorimotor control of speech production. We applied continuous theta burst stimulation (cTBS) over the anterior (aIFG) and posterior (pIFG) regions to investigate their roles in vocal motor control. A causal inference analysis (CIA) framework was developed to characterize source-space network organization. cTBS over both left aIFG and pIFG reduced vocal responses and enhanced P2 responses to pitch feedback perturbations, with no significant differences between two active stimulations. However, global dissimilarity analysis revealed greater P2-related topographic deviation from sham stimulation following aIFG stimulation than following pIFG stimulation. CIA further identified different source-space network patterns associated with aIFG and pIFG stimulation. These findings demonstrate the causal involvement of the left IFG in auditory-vocal integration and highlight the potential of CIA for characterizing distributed network organization underlying vocal motor control.