Event-related potentials in patients with temporal lobe epilepsy reveal topography specific lateralization in relation to the side of the epileptic focus

Event-related potentials (ERPs) were recorded during a continuous recognition memory paradigm in patients with left-sided (LTLE; n=8) or right-sided temporal lobe epilepsy (RTLE; n=6), and in healthy control subjects (n=24). Control subjects and both patient groups exhibited consistent OLD/NEW ERP-differences from 200–600 ms after stimulus onset. ERPs did not differ significantly between LTLE and RTLE patients, with respect to OLD/NEW distinction or the type of presented material (verbal vs. non-verbal). However, ERP topography showed significant differences between LTLE and RTLE patients: in lateral fronto-temporal recordings, patients showed larger negativities contralateral to the seizure focus, whereas we found larger negativities ipsilateral to the seizure focus in parietal recordings. Differences between the groups were significant from 300 to 600 ms post-stimulus. As a consequence, the amplitude gradient from fronto-temporal to parietal recordings was higher on the right side in LTLE patients and on the left side in RTLE patients. Again, differences between LTLE and RTLE patients were highly significant. We assume that ERPs reflect disturbances of a cortico-cortical network dependent on the side of the seizure focus in temporal lobe epilepsy. Furthermore, scalp-recorded ERPs might be a useful tool in the prediction of the side of the seizure focus in patients with temporal lobe epilepsy.