A NOVEL ENDOSCOPE DESIGNED FOR RECORDING NEURONAL ACTIVITY IN DEEP BRAIN REGIONS OF FREELY-BEHAVING ANIMALS WITH REDUCED INVASIVENESS

Optical methods based on thin multimode fibers (MMFs) are promising tools for measuring neuronal activity in deep brain regions of freely moving mice with limited invasiveness. However, current methods are limited. While fiber photometry only provides ensemble activity, imaging techniques using long MMFs are highly sensitive to bending and have not yet been applied to unrestrained rodents. Here, we present a new approach that combines a short MMF and a miniscope, and that relies on disentangling single-source time traces transmitted by the MMF using a general unconstrained non-negative matrix factorization algorithm [1].
To demonstrate the validity of the method, we conducted proof-of-concept in vitro experiments using a sample of fluorescent beads mimicking a set of active neurons with known activity patterns. The beads are illuminated by a light beam shaped by a digital micromirror device according to selected temporal patterns representative of calcium traces measured in neurons. Using this sample, we demonstrated that spatiotemporal fluorescence signals from >20 fluorescent sources transmitted by a thin (200µm) and short (8mm) MMF could be successfully disentangled. Similar results were obtained when the bead sources were buried behind a scattering media, and when we introduced neuropil signal stronger than the signal corresponding to the mimicked cell bodies. Furthermore, we showed that open-source miniscopes have sufficient sensitivity to image the same fluorescence patterns seen in our proof-of-principle experiment. Therefore, these results suggest a new approach to deep brain studies in freely moving mice with minimal invasiveness.
[1] Rimoli et al, Nature Communications 15, 6286 (2024)