Abstract
Objective. Fluorescence imaging through head-mounted microscopes in freely behaving animals is becoming a standard method to study neural circuit function. Flexible, open-source designs are needed to spur evolution of the method. Approach. We describe a miniature microscope for single-photon fluorescence imaging in freely behaving animals. The device is made from 3D printed parts and off-the-shelf components. These microscopes weigh less than 1.8 g, can be configured to image a variety of fluorophores, and can be used wirelessly or in conjunction with active commutators. Microscope control software, based in Swift for macOS, provides low-latency image processing capabilities for closed-loop, or BMI, experiments. Main results. Miniature microscopes were deployed in the songbird premotor region HVC (used as a proper name), in singing zebra finches. Individual neurons yield temporally precise patterns of calcium activity that are consistent over repeated renditions of song. Several cells were tracked over timescales of weeks and months, providing an opportunity to study learning related changes in HVC. Significance. 3D printed miniature microscopes, composed completely of consumer grade components, are a cost-effective, modular option for head-mounting imaging. These easily constructed and customizable tools provide access to cell-type specific neural ensembles over timescales of weeks.
Highlights
Optical recording of neural activity in the brains of behaving animals has become an essential method in systems neuroscience
Fluorescence from the sample returns through the objective, the dichroic, the emission filter (Chroma, bandpass filter, 535/50 nm, 4 mm × 4 mm × 1.05 mm) and an achromatic doublet lens (Edmund Optics, NT45-207, f = 15, 12.5 or 10 mm) that focuses the image onto the CMOS
While the axial resolution of multiphoton microscopy is vastly superior (Helmchen and Denk 2005), headmounted microscopes are often the only way to optically observe neural populations during naturalistic behaviors (Resendez et al 2016). The motivation for this project was that existing commercially-available miniature microscopes proved too heavy to consistently evoke undirected song, a learning-intensive motor behavior in zebra finches
Summary
Optical recording of neural activity in the brains of behaving animals has become an essential method in systems neuroscience. Increasingly widespread and powerful method employs miniature head-mounted fluorescence microscopes to record cellular resolution activity in freely moving animals (Ghosh et al 2011, Park et al 2011, Barbera et al 2016). Some exciting custom built and/or open-source options have emerged (Barbera et al 2016, Cai et al 2016), but the need remains for simple modular designs that use off the shelf parts and rapid prototyping tools. New features described in this project include an open-source 3D printed housing for easy experiment-specific reconfiguration, and wireless telemetry. For small animals such as juvenile mice or small songbirds that cannot carry the extra weight of the wireless transmitter and battery, we describe a torque-sensing motorized commutator based on 3D printed parts and low cost hardware. A wired configuration connected through the commutator enables an ultralight configuration for recording (Fee and Leonardo 2001)
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