Cats always land on their feet, but what makes them so agile? Their unique sense of balance has more in common with people than meets the eye. Researchers at the Georgia Institute of Technology are studying cat movement to better understand how the spinal cord works to help people with partial spinal cord injury walk and maintain balance.
Using a mix of experimental studies and computational models, the researchers show that somatosensory feedback, or neural signals, from special sensors in a cat’s body help inform the spinal cord about ongoing movement and coordinate the four limbs to prevent cats from falling when they encounter it. them. obstacles. Research shows that with sensory signals related to movement, the animal can walk even if the connection between the spinal cord and brain is partially broken.
Understanding the mechanisms of this type of balance control is especially important for older people who often have balance problems and can injure themselves in falls. Eventually, the researchers hope this could bring new insight into the role of somatosensory feedback in balance control. It could also lead to advances in spinal cord injury treatment because research suggests that activation of somatosensory neurons may improve the function of spinal nerve networks below the site of spinal cord injury.
«We are interested in the mechanisms that make it possible to reactivate injured networks in the spinal cord,» said Boris Prilutsky, Professor of the School of Biological Sciences. «We know from previous work that somatosensory feedback from the moving legs helps activate the spinal networks that control movement, ensuring steady motion.»
Although genetically modified mouse models have recently become dominant in the neural control of movement research, the cat model offers a significant advantage. Mice remain crouched when they move, meaning they are less likely to experience balance problems even if somatosensory feedback fails. Humans and cats, on the other hand, cannot maintain balance or even move if they lose sensory information about limb movement. This suggests that larger species such as cats and humans may have a different spinal nerve network organization that controls movement compared to rodents.
Georgia Tech collaborated with researchers at Sherbrooke University in Canada and Drexel University in Philadelphia to better understand how signals from sensory neurons coordinate the movements of the four legs. The Sherbrooke lab trained cats to walk on a treadmill at a pace consistent with human walking, and then used electrodes to stimulate their sensory nerves.
The researchers focused on the sensory nerve that transmits the sense of touch from the top of the foot to the spinal cord. By electrically stimulating this nerve, the researchers simulated hitting an obstacle and saw how the cats stumbled and corrected their movements in response. Stimuli were applied during the four periods of the gait cycle: mid stance, transition from stance to sway, medium sway, and transition from sway to stance. From this they learned that medium swing and the transition from stance to swing are the most important periods because stimulation increased activity in the muscles that flex the knee and hip joints, joint flexion and finger height, stride length, and stride duration. stimulated limb.
«To maintain balance, the animal must coordinate the movement of its other three limbs, otherwise it will fail,» Prilutsky said. Said. «We found that stimulation of this nerve during the swing phase increases the duration of the stance phase of the other limbs and improves stability.»
In fact, when the cat stumbles during the swing phase, this feeling triggers spinal reflexes as the swinging limb jumps over the obstacle, keeping the other three limbs on the ground and keeping the cat upright and balanced.
With these Canadian lab experiments, researchers at Georgia Tech and Drexel University are using the observations to develop a computational model of the cat’s musculoskeletal and spinal nerve control systems. The collected data is used to calculate somatosensory signals regarding the length, velocity and force produced of the muscles, as well as the pressure on the skin in all limbs. This information creates motion sensations in the animal’s spinal cord and contributes to inter-limb coordination by spinal cord neuronal networks.
«To help treat any disease, we need to understand how the intact system works,» Prilutsky said. Said. «That was one reason why this study was done so we could understand how the spinal cord networks coordinate limb movements and develop a realistic computational model of motion control of the spine. This will help us better know how the spinal cord controls movement.»
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