et al., 2010; Obien et al., 2015). Calcium imaging, using cell permeable dye (e.g. Fluo4-AM) or a genetically encoded indicator (e.g. GCaMP6) (Grienberger and Konnerth, 2012), offers single cell resolution as well as information on network activity. Compared to electrophysiology and MEA, Ca2+ imaging has a slower temporal resolution, in which action potential spikes are integrated over time. However, this temporal resolution has been sufficient to monitor activity in neuronal networks (Grienberger and Konnerth, 2012). The development of optical sensors for changes in voltage may overcome this limitation in the future (Marshall and Schnitzer, 2013).
