Associate Research Specialist University of Wisconsin-Madison
Rationale: Both complex partial (CPS) and generalized tonic-clonic (GTC) seizures lead to loss of consciousness (LOC), which carries serious risks of injury or death. To date, differences in mechanisms of LOC during GTC vs. CPS remain poorly understood. Here we compared the intracranial spectral signatures of LOC during CPS vs. GTC in human epileptic subjects. Methods: Intracranial recordings were obtained during 129 CPS and 50 GTC from 42 patients (19 female, age range 14-63, 101 temporal seizures). LOC could be quantified using the consciousness seizure scale (Arthuis, et al. 2009) in 35 CPS and 20 GTC. Ictal spectral values were computed for both CPS and GTC within first and second seizure halves and normalized by pre-ictal baseline for slow wave activity (SWA, i.e., delta power, 1-4 Hz), beta/delta ratio (15-25 Hz power over SWA), and high gamma power (HG, 80-150 Hz). Power spectrum was calculated separately for the seizure onset zone (SOZ), frontal, temporal, and parieto-occipital areas. Group statistics were performed using a linear mixed-effect (LME) model and p-values thresholded at p< 0.05 corrected for multiple comparisons using false discovery rate. Results: CPS were characterized by verbal and motor unresponsiveness in 84% and 75% cases, by failure to interact with the examiner in 34% of cases, and by unawareness of seizure 75% cases. GTC presented with verbal unresponsiveness, motor unresponsiveness, and failure to interact with the examiner in 100% cases, and unawareness of having a seizure in 90% cases.During the first half of CPS, SWA showed no significant change from baseline, while beta/delta ratio increased in SOZ and decreased in all other areas. HG increased in all regions except the frontal lobe, where it decreased. During the second half of CPS, both SWA and HG increased in all brain areas while beta/delta ratio further decreased in frontal and parieto-occipital areas. During the first half of GTC, SWA increased in SOZ, temporal, and frontal regions, while beta/delta and HG ratio increased in all areas, most prominently in SOZ (p< 0.001). During the second half of GTC, SWA was increased compared to baseline in all brain areas (p< 0.001); SWA was higher in parieto-occipital regions during the second half of GTC compared to CPS. Beta/delta ratio and HG further increased from the first to second half of GTC. The extent of HG increase was significantly higher for both seizure halves during GTC compared to CPS in all brain areas, including the SOZ. Conclusions: While CPS induces some degree of unresponsiveness and amnesia, altered consciousness is more consistent and more severe during GTC. Intracranially, behavioral evidence for deeper LOC was accompanied by stronger increases in SWA in the parieto-occipital cortex and by stronger increases in beta/delta ratio and HG power in all brain areas. These results suggest that deep LOC in GTC may occur through a different mechanism than during CPS, including a stronger ictal involvement of the posterior cortex. Funding: Please list any funding that was received in support of this abstract.: Tiny Blue Dot Foundation and Lily’s Fund for Epilepsy Research Grace Grant
