Alleviating Head-mounted Weight Burden for Neural Imaging in Freely-behaving Rodents Using a Helium-filled Balloon

The recently developed miniaturized head-mounted two-photon (2P) imaging devices have served as a valuable tool for neuroscientists, enabling real-time functional neural imaging in freely-behaving animals. Although the current 2P fiberscopes and miniscopes are lightweight, the weight of any potential additional accessories inevitably imposes a burden on the animal. Here, we present a buoyancy levitation method to alleviate head-mounted weight burden on mice. By utilizing the buoyance of a helium-filled balloon to counteract the additional weight of up to 7 g, both the motion behavior and neural activities remain unaffected by the added load. This easy-to-implement method provides a platform for studying neural network function in animals, effectively freeing them from the burden of head-mounted weight.