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 65 patients with unilateral TLE (37 with left hippocampal sclerosis (HS), 28 with right HS) and 20 healthy controls on a 3T GE-MRI scanner. 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. Results: Event-related fMRI analysis revealed significantly less activation in the left medial temporal lobe (MTL) in left TLE patients and significantly less right MTL activation in right TLE patients compared to controls. In left TLE patients, greater left than right hippocampal fMRI activation on encoding of words was correlated with better verbal memory performance on standard neuropsychological tests. In right TLE patients, greater right than left hippocampal fMRI activation on encoding of faces was correlated with better non-verbal memory performance. Earlier age of epilepsy onset correlated with greater contralateral hippocampal activation for both, verbal and non-verbal memory encoding. Conclusions: Our findings provide evidence for reorganization of hippocampal function to the contralateral side. Depending on the age of epilepsy onset, verbal and non-verbal memory function in the damaged, ipsilateral hippocampus is partly carried out by the contralateral hippocampus.