The cognitive impact of epileptiform EEG-discharges; relationship with type of cognitive task.

In this study we analyzed the effect of differing task dimensions (high vs. low information demand; short vs. long testing duration) on the occurrence of epileptiform EEG-discharges and the cognitive impact of such discharges. We performed this study only in patients with focal discharges as this appears to be the most complicated group to assess any relationship between epileptiform EEG-discharges and cognitive impairment. Seventeen patients with focal discharges in the EEG and an established diagnosis of localization-related (partial) epilepsy were included. The following tasks were used: Low information demand: auditory and visual RT; high information demand: BCRT and CVST. Short testing duration: Arithmetic and Reading; long testing duration: Vocabulary and Block Design. The percentage of patients with epileptiform EEG-discharge and EEG-related cognitive impact were compared using Chi-square testing. The occurrence of epileptiform EEG-discharges was not associated with one of the experimental conditions introduced in our study, that is, high/low information demand or short/long testing period. Also the difference between computerized reaction-time measurement and more traditional 'paper and pencil tasks' such as reading was not statistically significant. The only statistical significant difference was the more frequent occurrence of epileptiform EEG-discharges during tasks that used the visual input mode. In addition, we could identify one test that appeared to be particularly sensitive to direct cognitive effects of epileptiform EEG-discharges. Only for the CVST, the computerized visual searching task, the relationship with epilepsy-related cognitive impact is statistically significant. This test is the most mentally demanding test of the tests presented in our study and measures speed of visual information processing, using complex stimulus patterns and has a long testing duration. Our results do not confirm that any of the investigated task dimensions (high vs. low information demand; short vs. long testing duration) have a dominant effect on the occurrence of epileptiform EEG-discharges and the cognitive impact of such discharges. The effect found for the CVST suggest that three factors combined are necessary to assess the impact of epileptiform EEG-discharges on cognition: visual input mode, longer testing duration and high information processing demand.