Role of fronto-striatal tract and frontal aslant tract in movement and speech: an axonal mapping study

Abstract

Despite a better understanding of their anatomy, the functional role of frontal pathways, i.e., the fronto-striatal tract (FST) and frontal aslant tract (FAT), remains obscure. We studied 19 patients who underwent awake surgery for a frontal glioma (14 left, 5 right) by performing intraoperative electrical mapping of both fascicles during motor and language tasks. Furthermore, we evaluated the relationship between these tracts and the eventual onset of transient postoperative disorders. We also performed post-surgical tract-specific measurements on probabilistic tractography. All patients but one experienced intraoperative inhibition of movement and/or speech during subcortical electrostimulation. On postoperative tractography, the subcortical distribution of stimulated sites corresponded to the spatial course of the FST and/or FAT. Furthermore, we found a significant correlation between postoperative worsening and distances between these tracts and resection cavity. A resection close to the (right or left) FST was correlated with transitory motor initiation disorders (p = 0.026), while a resection close to the left FAT was associated with transient speech initiation disorders (p = 0.003). Moreover, the measurements of average distances between resection cavity and left FAT showed a positive correlation with verbal fluency in both semantic (p = 0.019) and phonemic scores (p = 0.017), while average distances between surgical cavity and left FST showed a positive correlation with verbal fluency scores in both semantic (p = 0.0003) and phonemic modalities (p = 0.037). We suggest that FST and FAT would cooperatively play a role in self-initiated movement and speech, as a part of "negative motor network" involving the pre-supplementary motor area, left inferior frontal gyrus and caudate nucleus.

Frontal aslant tract projections to the inferior frontal gyrus

“…In dominant hemisphere FAT is associated with the initiation of speech and the fluency [9,12]. Speech arrest was observed in frontal lobe tumours infiltrating FAT as well as during its intraoperative electrical stimulation in awake surgeries [11,16]. FAT disconnection is attributed to stuttering, progressive aphasia or the development of Fox-Chavany-Marie syndrome [5,13].…”

Damage to the Frontal Aslant Tract Accounts for Visuo-Constructive Deficits in Alzheimer’s Disease

“…This hypothesis is supported by the strong anatomical association between FAT and the frontal-striatal tract (FST) [16], a bundle connecting the SMA and pre-SMA with caudate nucleus [50] and involved in motor control, including manual coordination [16]. In its rostral part (around pre-SMA) the FAT is intermingling and overlapping with FST [16], whereas, caudally, FAT is running in a little more anterolateral side than FST [16]. Moreover, the present findings are supported by recent evidence of the role played by FAT in the visually guided hand movements [51], necessary to perform the grapho-motor task underlying the drawing tests.…”

“…We hypothesize that the FAT might also be involved in the planning of the motor engrams needed to execute the grapho-motor movements necessary to produce a drawing, and that the praxis deficits observed in AD are therefore in line with what has been observed in agrammatic-PPA patients. This hypothesis is supported by the strong anatomical association between FAT and the frontal-striatal tract (FST) [16], a bundle connecting the SMA and pre-SMA with caudate nucleus [50] and involved in motor control, including manual coordination [16]. In its rostral part (around pre-SMA) the FAT is intermingling and overlapping with FST [16], whereas, caudally, FAT is running in a little more anterolateral side than FST [16].…”

“…It is known that FAT plays a role in normal language development, as previously shown in young healthy individuals [13]. There is also some evidence that FAT is involved in language impairments due to primary progressive aphasia (PPA) [14], brain tumors [15,16,17], and stroke [18]. FAT is considered as a part of a "motor stream" mainly involved in speech production [19] and complementing the dorsal and ventral language streams [20].…”

Neuroplasticity and the brain connectome: what can Jean Talairach’s reflections bring to modern psychosurgery?

“…46,51 Extensive work on the most studied functions in intraparenchymal function have led to a more and more accurate description of this anatomy. For example, the inferior frontooccipital fasciculus, 3 frontal aslant tract, 54 uncinate fasciculus, 13 inferior longitudinal fasciculus, 3 different portions of the arcuate fasciculus, 13,61 and the way they interconnect with the past classic "eloquent cortical area" of language, are at least as important as the cortical functional anatomy to understand the possibility of recovery after surgery. Following this example, an extensive surgery of the left temporal pole involving the inferior longitudinal fasciculus and uncinate fasciculus (i.e., the core of the "indirect semantic ventral pathway") produces semantic troubles that will recover within a few weeks or months, only if the left inferior frontooccipital fasciculus is preserved (i.e., the core of the "direct semantic ventral pathway").…”