Role of frontotemporal fiber tract integrity in task-switching performance of healthy controls and patients with temporal lobe epilepsy

Abstract

The objective of this study is to investigate the relationships among frontotemporal fiber tract compromise and task-switching performance in healthy controls and patients with temporal lobe epilepsy (TLE). We performed diffusion tensor imaging (DTI) on 30 controls and 32 patients with TLE (15 left TLE). Fractional anisotropy (FA) was calculated for four fiber tracts [uncinate fasciculus (UncF), arcuate fasciculus (ArcF), dorsal cingulum (CING), and inferior fronto-occipital fasciculus (IFOF)]. Participants completed the Trail Making Test-B (TMT-B) and Verbal Fluency Category Switching (VFCS) test. Multivariate analyses of variances (MANOVAs) were performed to investigate group differences in fiber FA and set-shifting performances. Canonical correlations were used to examine the overall patterns of structural-cognitive relationships and were followed by within-group bivariate correlations. We found a significant canonical correlation between fiber FA and task-switching performance. In controls, TMT-B correlated with left IFOF, whereas VFCS correlated with FA of left ArcF and left UncF. These correlations were not significant in patients with TLE. We report significant correlations between frontotemporal fiber tract integrity and set-shifting performance in healthy controls that appear to be absent or attenuated in patients with TLE. These findings suggest a breakdown of typical structure-function relationships in TLE that may reflect aberrant developmental or degenerative processes.

Fig. 1

Fibers that project to the frontal lobe selected for the analysis. Top row shows the selected fibers from superior horizontal and mid-sagittal views. Middle and bottom rows present the individual fibers from sagittal view. CING appears in blue; UncF in green; ArcF in red and IFOF in orange.

Fig. 2

Scatter plots showing significant fiber FA and task-switching performance association. Top row shows the relationship between TMT-B performance and IFOF FA. Bottom row shows the relationship between VFCS and ArcF FA. Circles show values for health controls; squares for left TLE patients; triangles for right TLE patients. Best fit lines (solid: controls; dashed: left TLE patients; dotted-dashed: right TLE patients) approximate the correlational relationships per group. In both cases, a significant FA-task-switching performance is observed only for healthy controls.