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

Abstract

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 FAT's 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 FAT's 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.

A general role for ventral white matter pathways in morphological processing: going beyond reading

“…Of particular relevance is the case reported by Sierpowska and colleagues (2015), where damage to the left FAT elicited production errors characterized by inappropriate application of morphological rules. Taken together, these prior findings and the current results suggest that the role of the FAT in speech production may extend to high level language functions beyond its contribution to articulation and motor planning (Dick et al, 2019).…”

“…In contrast, no associations were found between the right FAT and verbal fluency in chronic stroke patients (Li et al, 2017). Considering these mixed findings and its cortical terminations, it has recently been postulated that the right FAT supports general inhibitory control (Dick et al, 2019). According to this view, the FAT supports the process of selecting a specific action program among several competitors that require the same motor resources.…”

The Supplementary Motor Area Responsible for Word Retrieval Decline After Acute Thalamic Stroke Revealed by Coupled SPECT and Near-Infrared Spectroscopy

“…The phonemic verbal fluency task recruits the left IFG [23] and pre-SMA/SMA [5,24]. Specifically, left FAT is associated with speech production, whereas right FAT is involved in executive function/inhibition control [25]. Both FAT pathways may be involved in sequential motor planning.…”

Is there any incremental benefit to conducting neuroimaging and neurocognitive assessments in the diagnosis of ADHD in young children? A machine learning investigation

“…In addition, it is part of a relatively recently identified fiber pathway, the frontal aslant tract (FAT). Recent work from our group (Dick et al, 2019;Garic et al, 2019) has implicated FAT to be an important potential moderator for ADHD related deficits in executive function. Our modeling results implicate SFG as a potential diagnostic region.…”