Cultured cortical networks exhibit a tremendous range of firing behavior. We are looking for regularities in their firing patterns, which we plan to use to control a simulated animal (the Neurally Controlled Animat; Potter group, SFN 2000 #467.20). To this end, neurons and glia from E18 rat cortex were dissociated and densely plated on planar MEAs (multi-electrode arrays) with 60 electrodes. We recorded daily from each dish for 30 consecutive days, starting one day after plating. Recurring dynamic patterns were observed on many timescales, from less than 100 ms through minutes. Single-cell action potentials were observed from the second day in vitro. Dish-wide bursts occurred as early as the fifth day. As the cultures matured, bursts became increasingly frequent. Isolated spikes, while increasing in absolute numbers, became an ever smaller part of the dishes' activity patterns. The dishes produced global bursts between one and 30 times per minute. Often, periodicity was maintained with few interruptions fo...