Abstracts

Rationale: Anterior temporal lobe resections (ATLR) benefit up to 70% of patients with intractable temporal lobe epilepsy (TLE) but may be complicated by material specific memory impairments, typically of verbal memory following left ATLR and non-verbal memory following right ATLR. The aim of this study was to use functional MRI (fMRI) to investigate specific memory functions in these patients.Methods: We scanned 53 patients with unilateral TLE (30 with left hippocampal sclerosis (HS), 23 with right HS) and 38 healthy controls on a 3T GE-MRI scanner; to date 32 patients have undergone surgery. All subjects performed an fMRI memory paradigm which examined the encoding of words, pictures and faces, allowing verbal and non-verbal memory encoding to be tested in a single scanning session. This task had previously demonstrated a material-specific lateralization of encoding in the medial temporal lobes (MTL) of healthy control subjects.Results: Event-related fMRI analysis revealed significantly less left MTL activation and relatively greater right MTL activation in left TLE patients compared to controls. Right TLE patients demonstrated less right MTL and greater left MTL activation compared to controls. In left TLE patients we found a positive correlation between fMRI activation in the left hippocampus on verbal encoding and verbal memory performance in standard neuropsycholgical tests. In right TLE patients right hippocampal fMRI activation on encoding of pictures was correlated with better non verbal memory.Conclusions: Pre-operative memory fMRI is a reliable and reproducible method to provide important additional information regarding organization of specific memory functions in patients with TLE to that provided by baseline neuropsychological tests. Correlation of pre-operative fMRI activation patterns with post-operative changes in memory in individual patients will determine whether pre-operative memory fMRI is a useful non-invasive predictor of post-operative memory decline following ATLR.