Silicon Photomultiplier-based Low-light in vivo Fiber Photometry

Fiber photometry is an important tool for studying neural activity in freely moving animals. Existing systems utilize photodetectors requiring a high bias voltage or high optical power. The former results in expensive bulky systems and the latter leads to photobleaching or phototoxicity. We present a low-light fiber photometry system for recording neural activity in mice. Employing a sensitive silicon photomultiplier (SiPM) allows the use of low excitation light without requiring high-voltage power supplies. Isosbestic wavelength control was implemented to correct for motion artifacts. The same control signal was used as a novel method for SiPM gain correction, eliminating the need for additional sensors and control mechanisms. An off-the-shelf impedance measurement integrated circuit was used to simplify the electronics for homodyne detection of light. Sensitivity, dynamic range, and robustness to artifacts were characterized by measurement of fluorescence in fluorescein solutions. In vivo measurements during footshock experiments validated the system’s effectiveness at 2.3 μW excitation power. The system’s power requirements show promise for miniaturization and animal-mountable configurations.