Extended Data Fig. 8: Backbone sequences observed during spontaneous population bursts in murine cortical organoids.

a, Raster plot visualization of single-unit spiking (blue dots) measured across the surface of a murine organoid (MO1) recorded at 42 DIV, positioned on top of the same type of microelectrode array as used for the recordings included in the main figures. The population firing rate is shown by the red solid line. Population bursts are marked by sharp increases in the population rate. Burst peak events are denoted by local maxima (black dots) that exceed 4x-r.m.s. fluctuations in the population rate. The shaded gray regions denote the burst duration window as defined by the time interval in which the population rate remains above 10% of its peak value in the burst. b, The instantaneous firing rate of single-unit activity from panel a after reordering. The backbone units are plotted above the dashed line, while non-rigid units are plotted below the dashed line. In each category, units are ordered based on their median firing rate peak time relative to the burst peak, considered over all bursts in the recording. c, The average burst peak-centered firing rate measured across all burst events for the example recording of which part is shown in a. The burst peak is indicated by the dotted line. The unit order is the same as b. Please note the progressive increase in the firing rate peak time relative to the burst peak, as well as a spread in the active duration for units having their peak activity later in the burst. The average firing rate is normalized per unit to aid in visual clarity.