Extended Data Fig. 1: Example spiking activity recorded from each microelectrode array.
Example spike waveforms detected during a 10-s time window are plotted for each electrode (data were recorded on post-implant day 119). Each 8x8 grid corresponds to a single 64-electrode array, and each rectangular panel in the grid corresponds to a single electrode. Blue traces show example spike waveforms (2.1-ms duration). Neural activity was band-pass filtered (250–5000 Hz) with an acausal, 4th order Butterworth filter. Spiking events were detected using a −4.5 root mean square (RMS) threshold, thereby excluding almost all background activity. Electrodes with a mean threshold crossing rate of at least 2 Hz were considered to have ‘spiking activity’ and are outlined in red (note that this is a conservative estimate that is meant to include only spiking activity that could be from single neurons, as opposed to multiunit ‘hash’). The results show that many electrodes record large spiking waveforms that are well above the noise floor (the y axis of each panel spans 580 μV, whereas the background activity has an average RMS value of only 30.8 μV). In area 6v,118 electrodes out of 128 had a threshold crossing rate of at least 2 Hz on this particular day (113 electrodes out of 128 in area 44).
