A 60 electrode MEA (upper left) used to measure neural activity from a small network of cultured neurons. The upper right corner shows a magnified view of the array consisting of an 8×8 grid of 60 electrodes with living rat cortical neurons at 6 days in vitro. Each electrode is spaced 200 um apart and measures the extracellular potential of neurons nearby the electrode. Example of an extracellular action potential measured with a single electrode (window scale 100 ms×50 uV). Neurons on these arrays are spontaneously active producing synchronized bursts of activity throught their lifetime (up to two years).