Continuous monitoring of development activity changes in cultured cortical networks

During development, cortical neurons show highly synchronized spontaneous activity. This spontaneous activity probably reflects the mechanisms underlying proper network formation regulated by activity-dependent synaptic modification. To see long-term transitions in this spontaneous activity, we constructed a microelectrode-array (MEA)-based continuous monitoring system. Rat cortical neurons were cultured on MEAs with 64 embedded electrodes and maintained in a conventional CO₂ incubator. A perfusion system for medium changes and recording setup for electrical signals were directly connected to the MEA in the incubator. Culture medium was continuously perfused at a very slow rate (0.1 ml/h), which was quite effective at maintaining constant conditions without contamination. Using this system, we succeeded in recording spontaneous activity of cultured cortical networks, almost continuously from 5 days to more than 1 month in vitro. It was revealed that the spontaneous activity patterns showed transition from simple synchronized bursts to a complex mixture of multiple patterns, separated by a brief silent period at approximately 2 weeks in vitro.