Striatal fiber photometry reflects primarily non-somatic activity

Calcium recording via fiber photometry is commonly used as a proxy for recording population neuronal activity in vivo, yet the biological source of the photometry signal remains unclear. Here, using simultaneous in vivo extracellular electrophysiology and fiber photometry in the striatum, along with endoscopic 1-photon and 2-photon calcium imaging, we determined that the striatal fiber photometry signal reflects primarily non-somatic, and not somatic, changes in calcium.