What purpose do mouse tails serve?
The answer may be more complex than one might initially expect. Recent research conducted by the Okinawa Institute of Science and Technology (OIST) indicates that mouse tails have a more significant function than was previously recognized. Through innovative experiments employing a tilting platform, high-speed videography, and mathematical modeling, researchers have showcased that mice actively swing their tails, like a whip, to keep their balance. This insight not only broadens our knowledge of mouse physiology but could also enhance our understanding of balance disorders in humans, potentially leading to earlier detection and treatment of neurodegenerative conditions such as multiple sclerosis and Parkinson’s disease.
“Mice are a common subject in neuroscience due to their genetic, biological, and behavioral similarities to humans, yet the specific role of their tails has been somewhat of a mystery,” says Dr. Salvatore Lacava from the Neuronal Rhythms in Movement Unit at OIST, the primary author of the study published in the Journal of Experimental Biology. “By gaining a deeper insight into how healthy mice maintain their balance and refining the methods used to evaluate their performance, we can better investigate the neurological mechanisms at play and the potential treatments for issues affecting motor control and stability.”
Utilizing the tail for balance
For a long time, it was thought that mice used their tails merely as a passive counterbalance, akin to how you might lean your body on a bike while navigating bumpy terrain or sharp turns. “We dedicated considerable time to observing healthy mice,” Dr. Lacava recalls. “Instead of merely acting as a counterbalance, we discovered that their tails have a consistently proactive role in stabilizing them.” When the ground beneath them tilts, the team found that mice rotate their tails rapidly in the opposite direction. Despite the lightweight nature of the tail, the incredible speed at which it swings generates a substantial amount of angular momentum, helping to counteract any falling motion. “It’s similar to swinging a whip fast enough to pull yourself in the direction of the crack to prevent falling backward.”
Besides countering sudden changes in balance, the researchers observed that mice flick their tails continuously in the opposite direction to their movements while navigating narrow surfaces, helping them maintain equilibrium as they transverse. In more challenging scenarios, they also hold their tails at a lower angle, combining active and passive balance strategies.
The understanding of tail function in mice for balanced movement had previously been limited and often neglected in studies. “Although mice are essential for neuroscience research due to their similarities with humans, our findings highlight how factors such as tails—which we lack—can significantly impact research on conditions that do affect us,” points out Professor Marylka Yoe Uusisaari, the unit leader and co-author of the paper. By showcasing the active role of a mouse’s tail, this research sets a foundation for more accurate evaluations of balance in healthy mice, establishing a key reference point for studies on various balance-affecting conditions, including neurodegenerative diseases.
New challenges for mice and research
In addition to clarifying the function of mouse tails, the research team introduced a fresh experimental framework for testing mouse balance. The traditional approach was a beam-walking test where mice had to traverse a 1cm wide beam under different conditions; falling off would classify them as off-balance. However, for healthy mice, this test is relatively simple. As Prof. Uusisaari explains, “many mouse species are arboral creatures that thrive in trees, effectively adapting to crossing slim branches. Our new setup raises the stakes by presenting narrower beams and unexpected movements.”
The newly designed setup features a variety of platform widths, ranging from 1cm down to 4mm, along with random rotations of 10 to 30 degrees in either direction. Rather than merely measuring whether the mice can remain on a beam, balance is redefined as how effectively a mouse’s body is aligned over its feet. To capture the intricate details of their movements, a biomechanical model based on a neural network was created to monitor the positioning of different body parts as they navigate the platform. This model allowed researchers to compute the tail’s angular momentum in relation to the body’s tilt and demonstrate how it mitigates this tilt.
“We aim to identify and address balance issues in humans before they escalate to the point where individuals struggle to walk straight,” Dr. Lacava summarizes. “With this study, we’ve established a similar benchmark for mice.” By illustrating the importance of mouse tails in their movement and enhancing experimental scrutiny for healthy mice, researchers are now better prepared to detect subtle shifts in balance performance, providing greater precision in examining the initial impacts of neurodegenerative diseases.
