The frontal aslant tract underlies speech fluency in persistent developmental stuttering

Area of Science:

• Neuroscience
• Speech Science
• Neuroimaging

Background:

• The frontal aslant tract (FAT) is a recently identified white matter pathway connecting the inferior frontal gyrus with speech motor areas.
• The FAT is proposed to be part of a motor stream critical for speech production.
• Persistent developmental stuttering is a speech disorder characterized by disruptions in speech fluency.

Purpose of the Study:

• To investigate the role of the frontal aslant tract (FAT) in speech fluency.
• To examine microstructural properties of the FAT in adults who stutter (AWS) using diffusion imaging.
• To determine if FAT alterations correlate with speech fluency deficits in AWS.

Main Methods:

• Diffusion tensor imaging (DTI) and tractography were used to quantify FAT volume and diffusion properties.
• Measures were also extracted from the corticospinal tract (CST) for comparison.
• Diffusion measures along the FAT and CST were correlated with behavioral measures of speech fluency in AWS and fluent controls.

Main Results:

• Adults who stutter (AWS) exhibited increased mean diffusivity in bilateral FAT compared to fluent controls.
• Specific regions within the left FAT and left corticospinal tract (CST) showed increased diffusivity in AWS.
• In AWS, increased diffusivity in left FAT sub-regions negatively correlated with speech fluency measures.

Conclusions:

• Findings suggest that microstructural alterations in the frontal aslant tract (FAT) are associated with persistent developmental stuttering.
• This study provides the first evidence linking the FAT to fluent speech production in stuttering.
• The results contribute to understanding the neural basis of stuttering and the functional role of the FAT in speech production.