Seizures and arousals from sleep--which comes first?

Epileptic seizures may be associated with arousals from sleep. The temporal sequence of seizures and arousals is often uncertain and it may be impossible to determine their relationship by surface electroencephalogram (EEG) recordings alone. We describe a 28-year-old right-handed man with medically refractory partial epilepsy in whom seizure onset appeared to follow arousal from stage 2 nonrapid eye movement sleep based on the surface EEG. Inspection of simultaneously recorded intracranial EEG, however, demonstrated that the seizure onset preceded the arousal. This study illustrates the limitations of surface EEG and the utility of intracranial electrode recordings in investigating the relationship between arousals and seizures.