Low and high frequency signatures of impaired consciousness in temporal lobe seizures

Impaired consciousness is a debilitating and unpredictable outcome of mesial temporal lobe seizures whose mechanisms to date remain unclear. Moreover, questions about the relationship between impaired consciousness and lateralization, hemispheric spread and electrophysiological characteristics of seizures are yet to be answered. To address these gaps, we conducted in-depth investigation of behavioral and intracranial EEG data from 186 mesial temporal lobe seizures of 51 patients with intractable mesial temporal lobe epilepsy. We found that bilateral mesial temporal spread of seizures is not a necessary condition for impaired consciousness, although seizures with bilateral mesial temporal involvement were significantly more likely to have impaired consciousness than unilateral seizures. Contrary to prior belief, we found no relationship between the onset side (left vs. right temporal lobe or language dominant vs. non-dominant lobe) of seizures and the probability of impaired consciousness. Lastly, we established that widespread increases in slow-wave activity (delta band) in extratemporal cortical areas, as well as increases in fast activity (beta band) in the temporal lobes were both robust markers of seizures with impaired consciousness and could predict ictal impairment with up to 86% accuracy. Our findings shed new light on networks that underlie impaired consciousness in temporal lobe epilepsy and may help guide deep brain stimulation of such systems (e.g. via thalamic nuclei) as a potential intervention to improve consciousness during seizures.