Two-photon fiberscope with a proactive optoelectrical commutator for rotational resistance-free imaging in freely behaving rodents.

Significance: The recently developed two-photon (2P) fiberscope offers attractive opportunities in neuroscience by enabling high-resolution neural imaging in freely behaving rodents. However, like other miniature 2P devices, it involves a tether (for fiber and scanner drive wires), which inevitably limits the animal's movement, especially its rotation. Aim: We aim to develop a platform for 2P fiberscopes (and other tethered miniature devices), enabling rotational resistance-free neuroimaging in freely rotating/walking rodents. Approach: We introduced a proactive optoelectrical commutator (pOEC) capable of real-time sensing and compensation for a tiny torque buildup in the tether (with a preselected threshold), preemptively eliminating the rotational resistance when the mouse physically rotates the fiberscope. Results: Experimental results demonstrated that the pOEC effectively compensates for torque buildup in the fiberscope, thereby maintaining stable 2P imaging performance. In addition, the system minimizes the rotational resistance imposed by the head-mounted tether, enabling near-zero rotational burden during 2P neural imaging in freely behaving mice. Investigations of neural activity further revealed that a considerable proportion of motor cortex neurons exhibited statistically significant changes in their firing patterns when the mouse was restricted by tether-induced rotational resistance or completely immobilized via head fixation. Conclusions: The results indicated that rotational restriction induced visible impacts on neuronal activities. Our platform offers a promising opportunity for studying dynamic neural circuit functions under nearly natural conditions with minimized impacts by the rotational restriction.