The frontal aslant tract (FAT) is a pathway that connects the inferior frontal gyrus with the supplementary motor area (SMA) and pre-SMA. The FAT was recently identified and introduced as part of a “motor stream” that plays an important role in speech production. In this study, we use diffusion imaging to examine the hypothesis that the FAT underlies speech fluency, by studying its properties in individuals with persistent developmental stuttering, a speech disorder that disrupts the production of fluent speech. We use tractography to quantify the volume and diffusion properties of the FAT in a group of adults who stutter (AWS) and fluent controls. Additionally, we use tractography to extract these measures from the corticospinal tract (CST), a well-known component of the motor system. We compute diffusion measures in multiple points along the tracts, and examine the correlation between these diffusion measures and behavioral measures of speech fluency. Our data show increased mean diffusivity in bilateral FAT of AWS compared with controls. In addition, the results show regions within the left FAT and the left CST where diffusivity values are increased in AWS compared with controls. Last, we report that in AWS, diffusivity values measured within sub-regions of the left FAT negatively correlate with speech fluency. Our findings are the first to relate the FAT with fluent speech production in stuttering, thus adding to the current knowledge of the functional role that this tract plays in speech production and to the literature of the etiology of persistent developmental stuttering.
Bibliographical noteFunding Information:
This work was supported by the Israel Science Foundation (ISF grant 513/11 awarded to M.B.-S and O.A) and by the Israeli Center of Research Excellence in Cognition (I-CORE Program 51/11 of the Planning and Budgeting Committee). O.C. was supported by the Israeli Ministry of Immigrant Absorption. We thank the Israeli Stuttering Association (AMBI) for their help with participant recruitment. We thank the team at the Wohl institute for advanced imaging in Tel Aviv Sourasky Medical Center, for their assistance with protocol setup and MRI scanning. We thank Jason Yeatman for his assistance with adjustments in the AFQ code. Finally, we are grateful to Prof. Yaniv Assaf and to Maya Yablonski for their helpful comments. The authors declare that there are no conflicts of interest.
© 2014, Springer-Verlag Berlin Heidelberg.
- Corticospinal tract
- Diffusion imaging
- Fiber tracking
- Frontal aslant tract
- White matter