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

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.