Abstracts

Rationale: Sleep-wake states (SWS) affect localization of the presumed epileptic source, with implications for resective surgery. Although rapid eye movement sleep (REM) reportedly has unique spatiodynamical features that may be used in localizing a potential epileptic source, there may be differences in this regard between the sub-states of phasic and tonic REM. We tested the extent to which phasic and/or tonic REM spatially agreed (overlap) or disagreed (non-overlap) with the cortical source localizations of other sleep-wake states.

Methods: From a prospectively recruited pool of epilepsy monitoring unit patients, we identified 7 patients with spikes in both phasic and tonic REM; 4 of whom also had spikes in each of non-REM1 (N1), N2, N3, and wakefulness (6 SWS total). We analyzed 271 spikes, sorted by SWS, from 66 day-night recordings. Spikes underwent electrical source localization (ESL) by standardized low-resolution electromagnetic tomography analysis (sLORETA) to yield source localizations of spikes arising in each SWS for each patient. ESL results were mapped to cortical grey matter (CGM) in individualized 3-D brain models using recent MRI when possible (n=6). Results reported as mean±standard deviation. Student’s two-tailed t-test compared 2 SWS at a time, and one-way ANOVA compared 6 SWS at a time, with significance level p≤0.05.

Results: The 6 SWS unanimously localized to a shared region of 14.1±10.2% individualized CGM, with each SWS contributing a similar proportion (36.5±26.6%, p=0.901) of its localization to this 6-way-concordant zone. Beyond unanimously localized cortex, SWS localizations dynamically agreed and disagreed. The degree to which the source localizations of any given SWS spatially agreed (CGM overlap) with those of any other one SWS was not significantly different (70.9%±17.2%, p=0.661). However, among patients with spikes in 6 SWS, tonic REM significantly revealed 5.6 times more unique source localizations (i.e. CGM that was not localized by any other SWS in that patient) as a fraction of its source localizations than phasic REM (0.051±0.014 vs. 0.0091±0.0028, p=0.023). Similarly, tonic REM strongly trended to revealing 7.5 times more unique source localizations than phasic REM as a fraction of CGM (0.025±0.018 vs. 0.0034±0.00178, p=0.0502).

Conclusions: SWS activate and deactivate epileptic sources as identified by ESL, dynamically agreeing and disagreeing about which cortical regions are responsible for starting seizures. Our finding that tonic REM offers a greater extent of unique source localizations compared to phasic REM has implications for epilepsy pre-surgical evaluation, and characterizing the underlying sub-state neurophysiology. Tonic, but not phasic, REM’s propensity for unique localizations warrants further study, including the assessment of whether more unique localizations translate into more frequently “correct” localizations following resective surgery.

Funding: Please list any funding that was received in support of this abstract.: Health Sciences Centre Foundation (Winnipeg), University of Manitoba; Mathematics of Information Technology and Complex Systems.