Genetically‑encoded calcium indicators (GECIs) are essential for studying brain function, while voltage indicators (GEVIs) are slowly permeating neuroscience. Fundamentally, GECI and GEVI measure different things, but both are advertised as reporters of “neuronal activity”.  Dr. Srdjan D. Antic, associate professor, recently published “Population imaging discrepancies between a genetically-encoded calcium indicator (GECI) versus a genetically-encoded voltage indicator (GEVI)”, which compares these two indicators in detail and is now available for all to read at https://rdcu.be/cggFE.