Abstracts

Rationale: Interictal epileptiform discharges (IEDs) represent the signature of an individual's increased seizure tendency. It has been a common belief that IEDs have no clinical correlates, thus they are always defined as "subclinical" or "interictal". The aim of our study is to study the cognitive functions of the specific brain area where IEDs are present. Methods: A patient with epileptic encephalopathy and frequent long-bursts of IEDs originating from the right occipital region was studied. In order to test the impacts of IEDs on cognitive function, the patient was subjected to button-press visual and auditory reaction time (RT) tasks, as well as to auditory and visual evoked potentials (AEPs, VEPs) tests. Additionally, the patient also underwent a neuropsychological evaluation. Results: RT was increased significantly when stimuli were given during IEDs as compared to during normal EEG. The increase of RT is much more prominent for visual tasks (median values: 263 vs 346.2 msec.) than for auditory tasks (median values: 227.2 vs 243.7 msec.). Visual stimuli given at the beginning of the discharges caused a prolonged RT, whereas they were not perceived by the patient when given in the middle of the discharges. VEPs were abnormal if recorded concomitantly during IEDs. However, AEPs showed no difference between during normal EEG and during IEDs. Neuropsychological evaluation showed cognitive impairments including visual agnosia, apraxia, visual-spatial short-term memory and visual imagery impairments. Conclusions: We demonstrated that posterior IEDs cause prolonged visual RT, non-perception of visual stimuli and abnormal VEPs. These findings suggest that IEDs transiently disrupt certain domains of cortical function, and they may cause long-term cognitive impairments seen in patients with epileptic encephalopathy.