Fast and sensitive GCaMP calcium indicators for neuronal imaging

We review the principles of development and deployment of genetically encoded calcium indicators (GECIs) for the detection of neural activity. Our focus is on the popular GCaMP family of green GECIs, culminating in the recent release of the jGCaMP8 sensors, with dramatically improved kinetics relative to previous generations. We summarize the properties of GECIs in multiple colour channels (blue, cyan, green, yellow, red, far‐red) and highlight areas for further improvement. With their low‐millisecond rise‐times, the jGCaMP8 indicators allow new classes of experiments following neural activity in time frames approaching the underlying computations. figure legend GCaMP calcium sensors are widely used to report neuronal activity via fluorescence readout.