Mechanical design of miniature head-mounted optical system for wireless photometry in mice
In basic neuroscience, fiber photometry is a method for monitoring neural activity in deep structures of the brains of awake and freely-moving animals (such as rats and mice), using fluorescence and genetic-targeting to record only from specific, experimentally relevant cells. An optical fiber relays excitation and emission light between the animal and a benchtop optoelectronic system. . This technology has matured to achieve ultra-low power operation for applications involving long-term and repeated measurements such as those related to learning and memory. The fiber tether, however, constrains the animal's motion and the ability to observe truly naturalistic behaviors, especially those related to social phenomena. Wireless photometry systems that operate without a tether have been proposed to address these challenges, but require high light levels that degrade the signal over time. This rules out applications like 24-hour homecage monitoring, where wireless photometry would otherwise be particularly useful.
In our lab, we have previously validated the use of a silicon photomultiplier (SiPM) as a highly-effective photodetector for wireless photometry, and are pursuing detailed electrical design with a group of electrical engineering students at UofC as part of their fourth-year capstone project. However, the optomechanical design and development of the miniaturized optical system, housing, and head-mounting mechanism remains an open question and critical challenge on its own.
We envision an optomechanical system that houses lenses, filters, LED lightsource, SiPM photodetector and port for an optical fiber. Ideally, the headstage would interface directly with a chronically-implanted optical fiber cannula, which would allow for direct comparison to systems involving an optical fiber tether. The housing, together with optical components, should weigh less than 1 g. Depending on the skills and interests of the team, there is also an opportunity to conduct the optical design through simulation tools.