Abstracts

Rationale: Neuropsychological deficits in temporal lobe epilepsy with hippocampal sclerosis (HS) regularly affect frontal lobe function. The origins of extra temporal cognitive deficits are multifaceted and include altered metabolism and structural connectivity, medication, seizure propagation and ongoing epileptic discharge. Our study intended to single out the role of interictal epileptic activity in executive dysfunction.Methods: Thirty four patients with unilateral HS (17 right, 17 left), all in the course of presurgical evaluation, underwent 3D high resolution T1 MR-imaging, video EEG monitoring and detailed neuropsychological testing. The latter comprised full scale IQ, verbal and non verbal memory and a large battery of tests for frontal lobe function, such as verbal and non verbal fluency, Brixton test of spatial anticipation, Wisconsin card sorting test, Stroop test. Hippocampi of patients were segmented via freesurfer and confirmed strictly unilateral atrophy. Surface video-EEG samples were collected during day time and sleep and were clinically analyzed for quantity and scalp distribution of spikes and sharp waves. Only spikes and sharp waves ipsilateral to the lesion were sufficiently abundant to calculate correlations. Their impact on cognitive scores was assessed with partial correlations, thus correcting for age, age of onset, disease duration and hippocampal volume in order to sort out the genuine role of interictal discharge.Results: We found a clear correlation between the number of temporal spikes and a large range of executive functions, notably in patients with left HS. Temporal and temporofrontal sharp waves were correlated with semantic and phonetic verbal fluency, graphical fluency and Brixton test of spatial anticipation in patients with left HS, and with semantic fluency and Wisconsin card sorting test in patients with right HS. In patients with left HS, semantic verbal fluency was well correlated with SW over the Broca region, whereas in patients with right HS, posterior temporal SW had greater impact.Conclusions: Temporal and temporofrontal interictal activity is correlated with diminished performance in a large range of executive functions. We suggest that epileptic discharge has a genuine impact on cognitive functions beyond the temporal lobe, most likely via alterations of frontotemporal interplay.