SWs coincide with cortical down-states and peak upward slope corresponds to the onset of down-states. (a) Example of single SW recorded across cortical layers by linear electrodes (with 20 µm spacing between the contacts). The channels are plotted and colored by depth. The top channel is located close to the surface, and the bottom channel (“depth”) is located 1,275 µm below. Left: Raw local field potential (LFP) traces. Middle: Delta-band filtered LFP. Right: Multiunit activity across all electrode channels; each line corresponds to a channel, and each dot represents the time of an extracellular spike detected on the channel. The density of spikes detected on all channels is evaluated using a 10 ms Gaussian kernel and plotted at the bottom. (b) Average LFP and multi-unit activity around the peak of all SW detected in a 2 h-recording session. Left: Average LFP trace for each depth. Middle: Spike count around the peak of the SW; each line corresponds to the cross-correlogram between the times of the peak of SW and the multiunit activity of a single channel. Right: Rasters of the total multi-unit activity detected across all channels for each individual SW (each line corresponds to a SW event, each dot on this line to an extracellular spike); a grand histogram is indicated at the bottom. Note that there is a clear drop in the density of spikes around the peak of each SW indicating the correspondence between the SW and cortical down-states. (c) The peak upward slope corresponds to the drop of multiunit cortical activity below the basal firing rate. The results of two mice are displayed. Top: Average SW waveform at the surface centered on the time of maximal slope of the SW. Middle: Average derivative of the surface LFP around the time of maximal slope of the SW. Bottom: Raster and histogram of the multi-unit activity for all SWs, centered on the maximal slope of each SW.