- Subjects with an unstable history of seizures cannot participate in the study. However, subjects who have been seizure-free for 6 months on a stable dose of anticonvulsant medication other than divalproex sodium or related formulations (e.g., depakene) may participate, along with non-medicated subjects with a history of seizures who have been seizure-free for 6 months. Subjects with abnormal EEG but no clinical seizures are also eligible.