Multi-electrode array (MEA)

One day before plating, 6-well MEA plates (Axion Biosystems, M384-tMEA-6W) were coated with poly-D-lysine (Millipore Sigma P6407-5MG) in borate buffer

,then washed six times with sterile water and aspirated prior use.

150,000 cells in a 15 µl drop were plated on a 6-well MEA plate. Cultures were maintained for 17-21 days at 37 °C in 5% CO2

On the day of recording, MEA plates were equilibrated for 10 min on the pre-warmer reader at 37 °C in 5% CO2

2 mins of firing activity was recorded at a 12.5 kHz sampling rate and filtered with a bandpass filter from 200 Hz to 2.5 kHz. Each MEA well contained 64 electrodes that detected changes in extracellular field potentials reflecting the spiking activity of neurons.Spike detection was performed with the adaptive threshold crossing algorithm with a threshold of 6× standard deviation using the AxIS software version 2.4 (RRID:SCR_016308) https://www.axionbiosystems.com/products/axis-software. All spike trains were exported from AxIS software.