Cell states involve constellations of co-expressed genes that enact cellular functions. In neurons, the most well-studied state involves the immediate early genes (IEGs), which are transcribed in response to the Ca2+ influx that follows action potentials (Bading, 2013; Hrvatin et al., 2017). IEG expression is largely uniform across neuronal types (Hrvatin et al., 2017) and brain regions and exhibits little background expression, making it straightforward to detect in the Drop-seq data.
