Structural Connectivity of Broca's Region

Objective: Investigate white matter connectivity between Broca’s region and frontal, inferior parietal, and temporal cortices using a novel diffusion tractography approach in 18 participants.Background: Based on evidence from aphasia, we hypothesized: (1) connectivity between Broca’s region and frontal cortex potentially supporting grammatic modification of phonological output; (2) two pathways connecting Broca’s region with postcentral cortex: a Broca’s region to posterior perisylvian cortex (PPC) pathway, and a Broca’s region to middle and inferior temporal gyri (MTG/ITG) pathway (via arcuate fasciculus); (3) two components to the pathway linking Broca’s region to PPC.Methods: Our novel tractography method represents local fiber orientations as Wishart distributions and allows successful modeling of crossing and branching pathways from high-angular resolution diffusion data (HARDI). Broca’s region consisted of pars orbitalis, triangularis, opercularis and inferior precentral gyrus (IPG).Results: Pars orbitalis and triangularis connected to anterior and middle portions of middle and superior frontal gyri. Pars opercularis and IPG connected with middle and posterior portions of frontal cortex. All divisions of Broca’s region were densely interconnected. Distinct pathways connecting Broca’s region with STG and MTG/ITG were identified. One pathway linked IPG to supramarginal gyrus (via arcuate fasciculus). A second connected pars opercularis and mid-superior temporal gyrus (via extreme/external capsule). A third linked pars opercularis and IPG to MTG/ITG via arcuate fasciculus. Finally, we found extensive connectivity between postcentral perisylvian areas linked to Broca’s region and both transverse gyrus and MTG/ITG.Conclusions: Our results show extensive connectivity between Broca’s region and frontal cortex that may support grammatic morphology. Pathways connecting Broca’s region with PPC may support sublexical sequence knowledge. Connections between Broca’s region and MTG/ITG may support naming via a whole word route, as the latter regions are likely involved in semantic processing. Postcentral perisylvian connectivity with transverse gyrus potentially incorporates the acoustic component into phonological sequence knowledge. Disclosure: Dr. Bohsali has nothing to disclose. Dr. Gullett has nothing to disclose. Dr. Mareci has nothing to disclose. Dr. Crosson has nothing to disclose. Dr. FitzGerald has nothing to disclose. Dr. White has received research support from Neuromuscular Engineering, Inc. Dr. Nadeau received personal compensation from Journal of the International Neuropsychological Society for serving as journal associate editor.