Combining structural equation modeling (SEM) and voxel-based morphometry (VBM), this study investigated the interactions among neural structures in the basal ganglia-thalamocortical circuit (BGTC) in the left hemisphere of stuttering and non-stuttering speakers. Stuttering speakers (n=12) and non-stuttering controls (n=12) were scanned while performing a picture-naming task and a passive-viewing (baseline) task. Results showed significant differences between stuttering and non-stuttering speakers in both effective connectivity and anatomical structures in the BGTC in the left brain. Specifically, compared to non-stuttering speakers, stuttering speakers showed weaker negative connectivity from the left posterior middle temporal gyrus (PMTG) to the putamen, but stronger positive connectivity from the putamen to the thalamus, from the thalamus to the PMTG and anterior supplementary motor area (preSMA), and from the anterior superior temporal gyrus (ASTG) to the preSMA. Accompanying such altered connectivity were anatomical differences: compared to non-stuttering controls, stuttering speakers showed more grey matter (GM) volume concentration in the left putamen, less GM volume concentration in the left medial frontal gyrus and ASTG, and less white matter volume concentration underlying the left posterior superior temporal gyrus inside the BGTC. These results shed significant light on the neural mechanisms (in terms of both functional connectivity and neural anatomy) of stuttering.

Using an fMRI-based classification approach and the structural equation modeling (SEM) method, this study examined the neural bases of atypical planning and execution processes involved in stuttering. Twelve stuttering speakers and 12 controls were asked to name pictures under different conditions (single-syllable, multi-syllable, or repeated-syllable) in the scanner. The contrasts between conditions provided information about planning and execution processes. The classification analysis showed that, as compared to non-stuttering controls, stuttering speakers' atypical planning of speech was evident in their neural activities in the bilateral inferior frontal gyrus (IFG) and right putamen and their atypical execution of speech was evident in their activations in the right cerebellum and insula, left premotor area (PMA), and angular gyrus (AG). SEM results further revealed two parallel neural circuits-the basal ganglia-IFG/PMA circuit and the cerebellum-PMA circuit-that were involved in atypical planning and execution processes of stuttering, respectively. The AG appeared to be involved in the interface of atypical planning and execution in stuttering. These results are discussed in terms of their implications to the theories about stuttering and to clinical applications.