Development of firing and bursting activity in dense cultures. A Median ASDR as a function of developmental age. Medians were taken across all 1800 one-second-wide time bins in individual half-hour long recordings. (Since bursts occupy a small fraction of time bins, a culture's median ASDR over time is a good indication of the baseline ASDR outside of bursts.) B Burstiness index as a function of developmental age. Dots in A and B are measurements from individual cultures, colored by plating batch. Black lines are interpolated averages across all cultures, using a Gaussian window with a half-width of 1 day. Dots were horizontally jittered by ± 0.25 days for visual clarity.