Abstracts

Rationale: Understanding loss of consciousness due to seizures and the underlying mechanism can have a positive impact on epilepsy patient care. Temporal lobe epilepsy has been the focus of previous research in focal epilepsy showing impaired consciousness to be associated with increased delta frequency slowing in the neocortex. The mechanism of impaired consciousness in focal frontal lobe seizures has been studied less, and is the goal of the present investigation. Methods: Our cohort of 14 patients undergoing intracranial EEG monitoring for surgical evaluation was obtained from Yale Comprehensive Epilepsy Center including 26 frontal lobe seizures confirmed by intracranial EEG monitoring. A Fast Fourier Transform was used to analyze each patient’s EEG from 30 second prior to seizure onset to 120 second after seizure onset with 1 second non-overlapping segments focusing on specific frequency bands: delta (0.5 to < 4 Hz), theta (4 to < 8 Hz), alpha (8 to 13 Hz), beta (>13 to < 25 Hz), and gamma (25-50 Hz). The fractional change of the power was calculated as (EEG power – Baseline Power) / Baseline Power defining baseline as 30 seconds prior to onset until seizure onset. The data were organized by ipsilateral and contralateral localizations to seizure onset and by eight localizations for each brain hemisphere. All statistics were two tailed unpaired t-tests with Holm-Bonferroni correction.  Results: We discovered that frontal lobe seizures with spared consciousness had significantly lower power than seizures with impaired consciousness. This occurred in all frequency ranges and for localizations both ipsilateral and contralateral to seizure onset (p < 0.05). The medial frontal lobe ipsilateral to the side of seizure onset did not show the same magnitude of difference between seizures with impaired and spared consciousness as seen in the rest of the brain. In contrast to the power, seizure duration was not significantly different for frontal lobe seizures with impaired vs. spared consciousness. Conclusions: This study suggests there is a less specific mechanism occurring with the propagation of EEG signals in frontal lobe seizures compared to temporal lobe seizures that impair consciousness. Unlike the decreased subcortical arousal producing cortical slow waves in temporal lobe seizures, frontal lobe seizures appear to impair consciousness due to widespread dissemination of ictal activity in a variety of frequency bands throughout the brain. It is our goal to aid in improving treatments and preventing loss of consciousness in frontal lobe seizures through our future investigations. Funding: James G. Hirsch M.D., Endowed Medical Student Research FellowshipYale University School of Medicine Medical Student Research FellowshipNational Institutes of Health-NHLBI Medical Student Research Fellowship