Interactions of epileptiform EEG discharges and cognition.

Interactions of subclinical epileptiform EEG discharges and cognitive functioning were studied in 91 patients with epilepsy, under video monitoring, to exclude overt clinical ictal phenomena during the investigations. A short-term memory test was presented as an engaging television game, in two versions, using spatial, or verbal material. Transitory cognitive impairment (TCI) was demonstrated during EEG discharges, either generalised or focal, in half the patients. Right-sided discharges were associated with impairment of the spatial task and left-sided with errors on the verbal version. TCI was demonstrable only when the discharge occurred during presentation of the material to be recalled. Increasing task difficulty, up to the patients' limit of performance, was associated with increasing susceptibility to TCI. Sixteen patients showed a significant effect of task on discharge rate, but in some this increased during the stimulus and in others while responding. There are thus complex interactions of epileptiform EEG activity on cognitive function and vice versa.