White matter fiber structural integrity in diffusion tensor imaging and executive function of patients with left temporal lobe epilepsy

Abstract

Objective To investigate the characteristics of executive dysfunction and its association with microstructural integrity of white matter fiber bundle in patients with left temporal lobe epilepsy (L-TLE) who have negative findings in conventional magnetic resonance imaging (MRI). Methods Executive function assessments, including Verbal fluency Test, Stroop Color Word Interference Test A~C (Stroop test, A~C), Trail Marking Test and Digit Span Test, were performed in 21 patients with L-TLE and 21 healthy control subjects. The patients and the control subjects underwent scanning with diffusion tensor imaging (DTI) to compare their fiber bundle fractional anisotropy (FA) and the mean diffusivity (MD) values. The correlation between the fiber bundles with microstructural alterations and the executive function score was analyzed. Results Compared with the control subjects, the patients with L-TLE had significantly lower scores for digit span forward (P=0.028) and verbal fluency (P < 0.001), and spent more time in Stroop C test (P=0.008). The patients with L-TLE showed significantly decreased FA values in the left anterior thalamic radiation, the left cingulate gyrus near the hippocampus and the forceps major, and increased MD values in the left anterior thalamic radiation, the bilateral cingulate gyrus, the left cingulate gyrus near the hippocampus, the forceps minor and the bilateral uncinate fasciculus compared with the control subjects. Correlation analysis showed that Stroop C test score was negatively correlated with the FA value in the left anterior thalamic radiation (r=-0.461, P=0.035) and positively with the MD value in the left anterior thalamic radiation (r=0.634, P=0.002); Verbal fluency was positively correlated with the FA value in the left-sided cingulate gyrus near the hippocampus (r=0.486, P=0.026) and negatively with the MD value in the left uncinate fasciculus (r=-0.513, P=0.017); Trail Marking Test B score was positively correlated with the MD value in the left anterior thalamus radiation (r=0.481, P=0.043). Conclusion The MRI-negative patients with L-TLE have executive dysfunction and damage of the white matter fiber bundles, especially the frontotemporal fiber bundle. Executive dysfunction in L-TLE patients is associated with abnormalities in the frontotemporal fiber bundles, and the abnormal connection in the frontotemporal fibrous structures is probably one of the contributing factors to executive dysfunction in MRI-negative patients with L-TLE.

Keywords

• temporal lobe epilepsy
• executive function
• fibrous connection damage
• diffusion tensor imaging
• white matter
• fiber structure