Abstracts

Rationale:
Consciousness is essential to normal human life, and its transient loss can have severe effects on morbidity and mortality. Impaired consciousness in focal temporal lobe seizures has been investigated in detail, however the mechanisms of impaired consciousness in frontal lobe seizures are not known. In this study, we used intracranial EEG to directly relate impaired consciousness in frontal lobe seizures to impaired behavioral responses as a marker of impaired consciousness.
Method:
We analyzed intracranial electroencephalography during 104 focal frontal onset seizures in 40 patients. Behavioral responsiveness was determined based on blinded review of video during seizures and classified into two main categories of impaired or unimpaired responsiveness to external stimuli. EEG signals from all electrodes were processed by fast Fourier transform, and signal power at different frequencies was calculated for each electrode. Signals were synchronized to time of seizure onset and signals averaged across electrodes within major anatomical regions. Fractional change [(EEG power—baseline power)/baseline power] from preictal baseline, was compared between seizures with impaired vs spared behavioral responsiveness.
Results:
Group data averages in different frequency bands (delta, theta, alpha, beta, and gamma) during seizure vs. baseline were analyzed for seizures, with (n = 54) and without (n = 50) impaired behavioral responsiveness. Seizures with impaired behavioral responsiveness had significantly longer mean duration than those without impairment. In addition, seizures with impaired behavioral responsiveness had greater high frequency EEG signal power in widespread brain regions bilaterally, and these increases reached statistical significance in the gamma frequency range (25 – 50 Hz).  
Conclusion:
These results suggest that broad increases in high frequency power throughout the cortex are associated with impaired consciousness in focal frontal lobe seizures. These findings contrast with impaired consciousness in focal temporal lobe seizures, where impaired consciousness is associated with widespread cortical slow wave (1-4Hz) activity. We can speculate that different focal seizure types produce impaired consciousness by impacting widespread cortical regions but through different mechanisms. The insights gained by studying mechanisms of impaired consciousness may be the first step towards developing novel treatments to prevent this important negative consequence of epilepsy.      
Funding:
:None