Fiber photometry has become the technique of choice for many researchers in neuroscience, because of its relative simplicity compared to other in vivo recording techniques, its high signal-to-noise ratio, and the ability to record in a variety of behavioral paradigms. It most commonly used in conjunction with genetically-encoded calcium indicators (GECIs, the GCaMP series) . GECIs change their ability to fluoresce based on whether or not they are bound to calcium. Because the internal concentration of calcium in neurons is very tightly regulated and voltage-gated calcium channels open when a neuron fires an action potential, transient increases in internal calcium concentration, which result in transient increases in the ability of a GECI to fluorescence, can be a good proxy for neuronal firing.