Dick, A. S. | bioRxiv Science

bioRxiv2018

The frontal aslant tract (FAT) and its role in speech, language and executive function

In this review, we examine the structural connectivity of a recently-identified fiber pathway, the frontal aslant tract (FAT), and explore its function. We first review structural connectivity studies using tract-tracing methods in non-human primates, and diffusion-weighted imaging and electrostimulation in humans. These studies suggest a monosynaptic connection exists between the lateral inferior frontal gyrus and the pre-supplementary and supplementary motor areas of the medial superior frontal gyrus. This connection is termed the FAT. We then review research on the left FATs putative role in supporting speech and language function, with particular focus on speech initiation, stuttering and verbal fluency. Next, we review research on the right FATs putative role supporting executive function, namely inhibitory control and conflict monitoring for action. We summarize the extant body of empirical work by suggesting that the FAT plays a domain general role in the planning, timing, and coordination of sequential motor movements through the resolution of competition among potential motor plans. However, we also propose some domain specialization across the hemispheres. On the left hemisphere, the circuit is proposed to be specialized for speech actions. On the right hemisphere, the circuit is proposed to be specialized for general action control of the organism, especially in the visuo-spatial domain. We close the review with a discussion of the clinical significance of the FAT, and suggestions for further research on the pathway.\n\nHighlightsO_LIThe frontal aslant tract (FAT) is a recently identified fiber pathway\nC_LIO_LIIt connects inferior frontal gyrus with medial frontal motor areas\nC_LIO_LIThe left FAT has been associated with speech and language function\nC_LIO_LIThe right FAT has been associated with inhibitory control\nC_LIO_LIBoth FAT pathways may function in sequential motor planning\nC_LI

neuroscience↗

bioRxiv2017

Laterality of the frontal aslant tract (FAT) explains externalizing behaviors through its association with executive function.

We investigated the development of a recently-identified white matter pathway, the frontal aslant tract (FAT) and its association to executive function and externalizing behaviors in a sample of 129 neurotypical children ranging in age from 7 months to 19-years. We found that the FAT could be tracked in 92% of those children, and that the pathway showed age-related differences into adulthood. The change in white matter microstructure was very rapid until about 6-years, and then plateaued, only to show age-related increases again after the age of 11-years. In a subset of those children (5-18-years; n = 70), left laterality of the microstructural properties of the FAT was associated with greater attention problems as measured by the Child Behavior Checklist (CBCL). However, this relationship was fully mediated by higher executive dysfunction as measured by the Behavior Rating Inventory of Executive Function (BRIEF). This relationship was specific to the FAT--we found no relationship between laterality of the white matter of the brain in general and attention problems, or executive function. These findings suggest that the degree to which the developing brain favors a right lateralized structural dominance of the FAT is directly associated with executive function and attention. This novel finding provides a new potential structural biomarker to assess attention deficit hyperactivity disorder (ADHD) and associated executive dysfunction during development.\n\nSignificance StatementTo investigate the function of a recently-identified white matter fiber pathway, the frontal aslant tract (FAT), we tracked the pathway in 129 typically developing children using diffusion-weighted magnetic resonance imaging (DW-MRI). We then examined whether laterality of the tract is associated with attention problems and executive function. We found that reduced right laterality of the tract was associated with greater executive dysfunction, which predicted increased reports of attention problems. The findings suggest that the degree to which the developing brain favors a right lateralized structural dominance of the FAT is directly associated with executive function and attention. This novel finding provides a new potential structural biomarker to assess attention deficit hyperactivity disorder (ADHD) and associated executive dysfunction during development.

neuroscience↗