A decrease in EEG energy accompanies anti-epileptic drug taper during intracranial monitoring

Objective: During intracranial EEG (icEEG) monitoring the likelihood of observing a seizure is increased by tapering anti-epileptic drugs (AEDs). Presumably AED taper results in an increase in cortical excitation which in turn promotes seizure emergence. We measured change in signal energy of icEEGs in response to AED taper to quantify changes in excitation which accompany the increased propensity for seizures. Methods: Twelve consecutive adult patients who completed intracranial monitoring were studied. Two icEEG epochs from before and after AED taper, each 1 h in duration, during wake, matched by time-of-day and removed from seizures were selected for each patient. Teager energy, a frequency weighted measure of signal energy, was estimated for both the seizure onset region as well as all other brain areas monitored. Results: Considerable changes in Teager energy, evaluated at a 1-h time-resolution, occur during intracranial monitoring. The most dominant trend is a decrease to lower values than those when the patient is on AEDs. A decrease of 35% was observed for both all the brain areas monitored and the seizure onset region. Conclusions: A decrease in signal energy occurs during intracranial EEG monitoring, possibly accompanying AED taper. If the decrease is due to AED taper this would suggest that AEDs prevent seizures in ways other than reduction of cortical excitation and seizure generation may be influenced by factors other than poorly regulated cortical excitation. (C) 2009 Elsevier B.V. All rights reserved.