THE PAPER IN BRIEF
• Genetically encoded calcium indicators (GECIs) are designer proteins that react to intracellular calcium-ion (Ca2+)influxes — which occur during the activation of neurons — by emitting light.
• GECIs have enabled researchers to gain myriad insights into the workings of the brain, but until now the proteins have lacked the precision to record a fundamental unit of activity, known as the action potential, in single neurons.
• Writing in Nature, Zhang et al.1 describe a GECI that marks a step towards solving this problem.