Fig. 2: Seizures recruit spiking bursts to a distinct subspace.

a Top: projection of spike sequences onto two-dimensional PCA space in the same example participant. Each dot represents a single spike sequence during a baseline burst (cyan), IED burst (red), and seizure burst (colored dark purple to light purple based on the time from the first detected seizure burst). The four seizure, two IED, and two baseline bursts from Fig. 1 are highlighted (gray, red, and blue rings). We identified the centroid of the baseline bursts in PCA space (cyan circle). Bottom: Identical projection of spike sequences demonstrating the progression of seizure bursts over time. Each arrow reflects the mean location in PCA space for seizure bursts over two consecutive three-second bins. b Average distance between seizure (sz) bursts and baseline centroid (purple bar, 0.38 ± 0.04, normalized arbitrary units), between IED bursts and baseline centroid (red bar, 0.16 ± 0.05), and between baseline (bl) bursts and baseline centroid (cyan bar, 0.11 ± 0.03) across participants and arrays. Seizure bursts are significantly farther from the baseline centroid than IED bursts or baseline bursts are (repeated measures one-way ANOVA; two-tailed p < 0.001, Holm-Bonferroni correction for multiple comparisons). c Normalized Euclidean distance in PCA space between seizure bursts and the baseline centroid over the course of this example seizure (three-second moving average in black; example seizure bursts from Fig. 1 highlighted with gray rings). Seizure bursts initially reside close to baseline bursts (cyan line indicates mean baseline distance to baseline centroid), but then abruptly diverge. d Initial, maximum, minimum, and final distances between seizure bursts and baseline centroids in each participant and array. e Initial, maximum, minimum, and final distances between seizure bursts and baseline centroids, normalized by the distances observed after shuffling the sequences of the seizure bursts, in each participant and array (see Supplementary Fig. 8). Seizure bursts travel farther from the baseline centroid at maximum (p = 0.003, two-tailed one-sample t test, p value unadjusted) and terminate farther away from the baseline centroid (p < 0.004) than would be expected by chance alone.