Twist-free ultralight two-photon fiberscope enabling neuroimaging on freely rotating/walking mice

Abstract

Lightweight and head-mountable scanning nonlinear fiberscope technologies offer an exciting opportunity for enabling mechanistic exploration of ensemble neural activities with subcellular resolution on freely behaving rodents. The tether of the fiberscope, consisting of an optical fiber and scanner drive wires, however, restricts the mouse’s movement and consequently precludes free rotation and limits the freedom of walking. Here we present the first twist-free two-photon fiberscope technology for enabling neuroimaging on freely rotating/walking mice. The technology equips a scanning fiberscope with active rotational tracking and compensation capabilities through an optoelectrical commutator (OEC) to allow the animal to rotate and walk in arbitrary patterns during two-photon fluorescence (TPF) imaging of neural activities. The OEC provides excellent optical coupling stability ( &lt;<!-- ± 1 % fluctuation during rotation) and an extremely high torque sensitivity ( &lt;<!-- 8 m N ⋅ m ). In addition, the new technology is equipped with a custom grating and prism to effectively manage the temporal properties of the femtosecond excitation pulses through the fiber-optic system, which improved neuroimaging signal by more than 2 X . This TPF fiberscope imaging platform has been tested for in vivo imaging, and the results demonstrate that it enables reliable recording of calcium dynamics of more than 50 neurons simultaneously in the motor cortices of freely behaving mice in a twist-free fashion. With active tracking function of the OEC enabled, we observed considerable increase in both behavior and neural activities in the motor cortices of the mice during freely behaving neuroimaging experiments.

Large-scale two-photon calcium imaging in freely moving mice

“…These constraints motivated attempts to develop a new generation of miniaturized 2P devices with resolution, speed, and z -scanning capability similar to those of 2P benchtop microscopes and an FOV close to that of 1P miniscopes ( Li et al., 2021 ; Ozbay et al., 2018 ; Wallace and Kerr, 2019 ; Zong et al., 2021 ; Zong et al., 2017 ). Of particular interest was the development of a new type of 2P miniscope that included (1) a hollow-core photonic-crystal fiber (HC-920) to deliver 920-nm femtosecond laser pulses, (2) a fast microelectromechanical systems (MEMS) scanner ( Milanovic et al., 2004 ) for fast point scanning, and (3) a supple fiber bundle to collect the fluorescence ( Zong et al., 2021 ; Zong et al., 2017 ).…”

Feasibility Analyses and Experimental Confirmation of Dove Prism Based Dual-fiberscope Rotary Joint

“…This means the rotation of a fiberscope can be compensated by rotating the Dove prism by a half angle so that the stationary incident beam can still be coupled into the rotated fiberscope after going through the half-angle rotated Dove prism; 4) The optical pathlength of any incident beams that are parallel with each other is a constant, which means a Dove prism does not introduce an optical pathlength difference among these beams. This is very favorable for 2P imaging since the material dispersion of the Dove prism for the incident femtosecond (fs) pulses can be conveniently pre-compensated, e.g., by using a grating-prism (GRISM) pair (for simultaneous compensation of the group velocity dispersion but for the third order dispersion as well) [16]. These key properties make a Dove prism a viable choice for a dual-fiberscope rotary joint.…”

Advances of optical miniscopes for in vivo imaging of neural activity in freely moving animals

“…In the work by Ozbay et al (2018) , the laser is spectrally broadened through a polarization maintaining fiber and pre-chirped using a grating pair pulse stretcher. Li et al (2021) use grating and prism to compensate for both material group velocity dispersion and third-order dispersion.…”

“…They also used an electrical rotary joint between the PMT and the optical fiber to further reduce the obstruction to the mice’s movement ( Zong et al, 2017 ). Li et al (2021) designed an optoelectrical commutator to allow mice to rotate and walk freely, which provides excellent optical coupling stability (≤±1%) fluctuation during rotation and high torque sensitivity (< 8 mN ⋅ m). Their work shows that when optoelectrical commutator tracking was enabled, not only the mice behaved more actively, but also the cortex neurons exhibited increased firing activities ( Li et al, 2021 ).…”