Abstract
The limbic system is presumed to have a central role in cognitive performance, in particular memory. The purpose of this study was to investigate the relationship between limbic white matter microstructure and neuropsychological function in temporal-lobe epilepsy (TLE) patients using diffusion tensor imaging (DTI). Twenty-one adult TLE patients, including 7 non-lesional (nlTLE) and 14 with unilateral mesial temporal sclerosis (uTLE), were studied with both DTI and hippocampal T2 relaxometry. Correlations were performed between fractional anisotropy (FA) of the bilateral fornix and cingulum, hippocampal T2, neuropsychological tests. Positive correlations were observed in the whole group for the left fornix and processing speed index. In contrast, memory tests did not show significant correlations with DTI findings. Subgroup analysis demonstrated an association between the left fornix and processing speed in nlTLE but not uTLE. No correlations were observed between hippocampal T2 and test scores in either the TLE group as a whole or after subgroup analysis. Our findings suggest that integrity of the left fornix specifically is an important anatomical correlate of cognitive function in TLE patients, in particular patients with nlTLE.
Highlights
Temporal-lobe epilepsy (TLE) is the most common focal epilepsy syndrome and is often associated with cognitive comorbidity in particular for patients with mesial temporal sclerosis (MTS) (Hermann et al, 2009)
Considering Auditory Verbal Learning Test delayed recall score (AVLT), for which the mean standard score is 50 (SD 10), both groups are within normal limits for AVLT but non-lesional TLE (nlTLE) patients scored higher (54) than unilateral mesial temporal sclerosis (uTLE) (42)
The primary observation of this study was that correlations were only observed between fractional anisotropy (FA) of the left fornix and processing speed for the TLE group as a whole with no correlations observed for the verbal (AVLT) and non-verbal (CVMT) memory tests nor for FA of the other tracts and any of the cognitive measures
Summary
Temporal-lobe epilepsy (TLE) is the most common focal epilepsy syndrome and is often associated with cognitive comorbidity in particular for patients with mesial temporal sclerosis (MTS) (Hermann et al, 2009). Previous magnetic resonance imaging (MRI) volumetric studies have demonstrated that cognitive deficits in TLE are most strongly predicted by white matter volume (Hermann et al, 2002, 2003). In vivo DTI of the fornix in TLE patients has shown histological correlates between fractional anisotropy (FA) and axonal membranes (Concha et al, 2010) thereby validating the technique as a non-invasive indicator of white matter micro-structural characteristics in human brain. In the Abbreviations: AVLT, Rey auditory verbal learning test recall score; CPMG, Carr Purcell Meibom Gill sequence; CVMT, continuous visual memory test total score; DTI, diffusion tensor imaging; FA, fractional anisotropy; MRI, magnetic resonance imaging; MTS, mesial temporal sclerosis; nlTLE, non-lesional temporal-lobe epilepsy; r(p) , Spearman rho correlation.; ROI, region of interest; SD, standard deviation; TLE, temporal-lobe epilepsy; uTLE, temporal-lobe epilepsy with unilateral mesial temporal sclerosis; WAIS-III, Wechsler adult intelligence scale third edition
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