Abstracts

Rationale: To build and validate the novel dynamic tractography-based model for localizing interictal spike sources and visualizing single-axonal spike propagations through the white matter.

Methods: We studied 1,900 spike events recorded in 19 patients with drug-resistant temporal lobe epilepsy (TLE) who underwent extraoperative intracranial electroencephalography (iEEG) and resective surgery. Twelve patients had mesial TLE (mTLE) without dual pathology. The remaining seven had lesional TLE, characterized by a magnetic resonance imaging-visible mass lesion in the temporal lobe neocortex. We identified the leading and lagging sites, defined as those initially and subsequently (but within ≤50 milliseconds) showing spike-related augmentation of broadband iEEG activity. In each patient, we estimated the sources of 100 spike discharges using the latencies at given electrode sites and diffusion-weighted imaging-based streamline length measures. We determined whether the spatial relationship between the estimated spike sources and resection would be associated with postoperative seizure outcomes. We generated movies presenting the spatiotemporal change of spike-related fiber activation sites by estimating the propagation velocity using the streamline length and spike latency measures.

Results: The spike propagation velocity from the source was 1.03 mm/ms on average (95% confidence interval: 0.91-1.15) across 133 tracts noted in the 19 patients. The estimated spike sources in mTLE patients with ILAE class 1 outcome were more likely to be in the resected area (83.9% vs. 72.3%; φ=0.137; p< 0.001) and in the medial temporal lobe region (80.5% vs. 72.5%; φ=0.090; p=0.002) than those associated with the class ≥2 outcomes. The resulting movie successfully animated spike propagations, which were confined within the temporal lobe in mTLE but involved extratemporal lobe areas in lesional TLE.

Conclusions: We, for the first time, provided dynamic tractography visualizing the spatiotemporal profiles of rapid propagations of interictal spikes through the white matter. Dynamic tractography has the potential to serve as a unique epilepsy biomarker.

Funding: Please list any funding that was received in support of this abstract.: This work was supported by the National Institutes of Health [grant number: NS064033 (to E.A.); NS089659 (to J.W.J.)] and JST CREST [grant number: JPMJCR1784 (to T.M.)].