(A) Experimental setting: brain slices were perfused with 10 nM Hm1a, a concentration at which Hm1a is selective for Na_V1.1 (Supplemental Figure 1), and CSD induction was monitored with extracellular LFP recordings and IOS imaging obtained in extended brain regions (4× objective, 0.35× camera adapter). (B) Representative LFP recording of a CSD observed in the neocortex during the perfusion with Hm1a. Scale bars: 1 mV, 20 seconds. (C) Overall results showing the lack of spontaneous CSD in control (0/17 slices), and success rate for neocortical induction with bath application of Hm1a (16/71), which never triggered CSD in other structures (Fisher’s exact test, Bonferroni correction, neocortex control versus neocortex Hm1a, *P = 0.04; neocortex Hm1a versus other structures’ Hm1a, ****P = 10^–4). (D) Upper left panel, raw transmitted light image of a representative coronal slice including the neocortex, the hippocampus, the dorsal striatum, the globus pallidus, and the thalamus; upper right panel, illustration of a whole hemisphere (Brain Explorer, Allen Institute) in which the imaged area is indicated by the circle (see Supplemental Figure 2 for additional details). The 4 bottom panels correspond to time series of image processing of IOS acquisitions (one image every 5 seconds, the first one 5 seconds after CSD initiation; see Methods), which show that CSD was triggered only in the neocortex. Scale bar: 500 μm. (E) Raw transmitted light image of another representative coronal slice including the neocortex, the dorsal striatum, the globus pallidus, and the thalamus (upper left); illustration of a whole hemisphere (Brain Explorer, Allen Institute) in which the imaged area is indicated by the circle (see Supplemental Figure 2 for additional details). The 4 bottom panels are a time series of processed IOS images, which show that CSD was triggered only in the neocortex. Scale bar: 500 μm (see Supplemental Video 1).