Abstracts

Rationale: A subset of individuals with temporal lobe epilepsy (TLE) have unexpected attention and executive impairments (e.g., adapting to and solving problems, inhibiting undesirable responses), as well as expected memory impairments. Previous studies suggest that these unexpected impairments are associated with structural abnormalities outside of the temporal lobe. Using diffusion tensor imaging (DTI), Wang et al. (2007) found that verbal fluency impairment in patients with TLE was associated with reduced fractional anisotropy (FA) of white matter in the left frontal lobe. Cingulum atrophy is found in individuals with epilepsy, especially in patients with left-sided TLE (Riederer al., 2008). The cingulum bundle is thought to be associated with working memory, emotional regulation, error detection, learning, and problem solving (Nestor et al., 2008; O’Sullivan et al., 2005; Sepulcre et al., 2009). The purpose of this study was to evaluate the relationship between executive functions and white matter tract integrity of the cingulum bundle using DTI in individuals with TLE. Methods: Eight patients (mean age of 37.3 years; six women) diagnosed with video-EEG confirmed intractable TLE (4 left, 4 right; mean duration of disease of 16 years) underwent DTI and neuropsychological assessment. FA was computed for the left and right cingulum bundles using AFNI and the ICBM WM Atlas. Neuropsychological tasks included measures of working memory, problem solving, mental flexibility, verbal fluency, and visual and verbal learning. Results: One-way ANOVA indicated that patients with executive dysfunction (z-score -1.64 below normative data) had significantly lower mean FA values. For example, the four patients with impaired mental flexibility had a lower mean FA value compared to patients with intact mental flexibility (impaired mean FA=0.30 [SD=0.05]; intact mean FA=0.44 [SD=0.04]; F[1,7]=24.6,p=0.003). Controlling for age, lower left cingulum FA values were significantly correlated with poorer working memory (r=0.82; see Figure 1), problem solving (r=0.73), mental flexibility (r= -0.83), lexical fluency (r=0.79), semantic fluency (r=0.87), and verbal learning (r=0.92; see Figure 2; all p values < 0.05). Spatial learning impairment was the only ability associated with lower right cingulum FA values (r=0.76, p=0.03). Conclusions: Cingulum bundle white matter tract disruption may partly explain why unexpected executive dysfunction exists in a subset of individuals with TLE.