Multifiber Array-Based Photometry System for Multiregional Functional Mapping in the Mouse Brain.

Mesoscopic functional brain mapping is essential for a better understanding of various brain functions and dysfunctions. However, accessing distributed neural circuits in mammalian brain regions remains a significant challenge. While fiber photometry is a versatile optical approach, existing methods often suffer from invasiveness and limited scalability. Here we present an affordable multifiber array (MFA)-based photometry system to monitor neural signals across multiple regions. Our system comprises a custom-designed MFA utilizing 50-μm diameter optical fibers and off-the-shelf optical components. To demonstrate the system's versatility, we monitored GABAergic population activity using jGCaMP8s across multiple brain regions in head-fixed, awake mice. By combining this approach with pupillometry, we identified state-dependent, region-specific GABAergic dynamics. Our MFA-based photometry system opens new avenues for investigating state-dependent neural dynamics at the mesoscopic level. To facilitate wider adoption, all code and resources are publicly available on GitHub (https://github.com/Sakata-Lab/MFA).