The impact of subclinical epileptiform discharges on complex tasks and cognition: relevance for aircrew and air traffic controllers.

Subtle seizures consisting of brief alteration of consciousness with or without automatisms may go unnoticed in daily life, but can be detected more easily with electroencephalographic (EEG)/video recordings. Generalized and partial epileptiform EEG discharges can nevertheless be subclinical (subclinical epileptiform discharges, SEDs). When appropriate complex tasks are presented, it has been shown that even very short SEDs of 0.5 second disrupt cognition. In daily life this has been shown during automobile driving: half of the subjects showed significant deviations in lateral position of the car during SEDs and made more errors in an attention task while driving. Individual differences in the cognitive effects of SEDs are, however, striking and may be partly due to interaction between level of performance and frequency of spontaneous EEG discharges, as has been shown in another driving study: about 75% of subjects showed suppression of SEDs by driving, which is a combination of sensory, mental, and motor activity. Not only can SEDs negatively influence performance, but in some cases mental activities can provoke epileptiform discharges. It is important to realize that these mechanisms exist and that only detailed EEG studies can clarify these issues. In air traffic controllers, brief alterations of consciousness and cognitive impairment have occurred but cannot be accepted for safety reasons; therefore, Eurocontrol has used the EEG as a screening tool since 1995.