Abstracts

Rationale: Temporal lobe epilepsy (TLE) is associated with significant, and often progressive memory impairment. We hypothesised that this dysfunction may result from disruption of critical white matter tracts leading to reduced functional connectivity between cognitive processing domains, and impairment in specific memory modalities. Methods: We acquired diffusion tensor MRI data in 25 left TLE subjects and 20 control subjects. All patients underwent verbal and non-verbal recall memory tests derived from the adult memory and information processing battery (AMIPB). Principal components analysis was used to derive two factors for verbal and non-verbal recall memory. Recognition memory testing consisted of the Warrington recognition test for words and figures. The vocabulary subtest of the WAIS III was used to derive a measure of semantic memory. All patients also had hippocampal volumes measured manually on T1 weighted images, and fMRI laterality indices derived from verbal fluency tasks. A whole brain analysis of fractional anisiotropy (FA) and mean diffusivity (MD) against verbal/non-verbal/semantic memory was carried out using tract based spatial statistics (TBSS). A region of interest analysis using probabilistic tractography was used to investigate the relationship between the fornix, uncinate fasciculus (UF), parahippocampal gyrus, cingulum and memory function. Results: The TBSS analysis of MD images revealed large clusters of voxels in the left uncinate fasciculus and fornix that were negatively correlated with verbal and non-verbal recall memory. No large clusters of voxels in the FA or MD images correlated with recognition memory or vocabulary scores. The tractography analysis confirmed the TBSS findings by demonstrating significant negative correlations between the left and right fornix MD and verbal and non-verbal memory respectively (p<0.05), and a positive correlation between left UF volume and vocabulary (p<0.05). In contrast there were no significant correlations seen between FA/MD in these tracts and recognition memory, nor between the cingulum/parahippocampal gyrus and any of the memory indices.