Cats are always on their feet, but what makes them so agile? Their unique sense of balance has more in common with humans than it seems. Georgia Tech researchers are studying cat locomotion to better understand how the spinal cord helps people with partial spinal cord injuries walk and maintain balance.
The researchers combined experimental studies and computational modeling to show that somatosensory feedback, or neural signals from specialized sensors throughout a cat’s body, helps inform the spinal cord of ongoing movement and coordinates the limbs to prevent the cat from falling when it encounters obstacles. With these sensory signals associated with movement, the study showed that the animals could walk even if the connection between the spinal cord and the brain was partially broken.
Understanding this type of balance control mechanism is especially important for older adults who often have balance problems and may be injured when they fall. Ultimately, the researchers hope this will shed new light on the role of somatosensory feedback in balance control. It could also lead to advances in the treatment of spinal cord injuries, as studies have shown that the activation of somatosensory neurons can improve the function of the spinal cord neural network below the site of spinal cord injury.
“We’ve been interested in mechanisms that can reactivate damaged networks in the spinal cord,” said Boris Prilutsky, a professor in the School of Biological Sciences. “We know from previous research that somatosensory feedback from moving the leg helps activate the spinal network that controls movement, allowing for stable movement.”
Although transgenic mouse models have recently dominated the study of neural control of locomotion, cat models offer an important advantage. When they moved, the mice remained crouched, meaning they were less likely to have balance problems even if somatosensory feedback failed. On the other hand, humans and cats 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 organization of spinal neural networks to control movement compared to rodents.
Georgia Tech teamed up with researchers at the University of Sherbrooke in Canada and Drexel University in Philadelphia to better understand how signals from sensory neurons coordinate the movement of the four legs. The Sherbrooke lab trained cats to walk on a treadmill at a pace consistent with a human gait, then used electrodes to stimulate their sensory nerves.
The researchers focused on the sensory nerves that carry the sense of touch from the top of the foot to the spinal cord. By electrically stimulating this nerve, the researchers simulated bumping into an obstacle, watching how the cats stumbled and corrected their movements in response. Stimuli were applied during four phases of the gait cycle: intermediate stance, transition from stance to swing, intermediate swing, and transition from swing to stance. From this, they learned that the mid-swing and the transition from stance to swing are the most important periods as stimulation increases the activity of the muscles that flex the knee and hip joints, joint flexion and toe height, stride length and stride length are affected. Stimulated limbs.
“To maintain balance, the animal has to coordinate the movements of the other three limbs, or it falls over,” Prilutsky said. “We found that stimulating this nerve during the swing phase increased the duration of the stance phase of the other limb and improved stability.”
In fact, when the cat stumbles during the swing phase, this sensation triggers a spinal reflex that ensures the other three limbs remain on the ground and keeps the cat upright and balanced while the swinging limb straddles the obstacle.
Through these Canadian laboratory experiments, researchers at Georgia Tech and Drexel University are using observations to develop computational models of the cat’s musculoskeletal and spinal neural control systems. The collected data is used to calculate somatosensory signals related to the length, speed and force generated by the muscles, as well as skin pressure on the extremities. This information forms the sensation of movement in the animal’s spinal cord and contributes to limb-to-limb coordination of the spinal neuronal network.
“To help treat any disease, we need to understand how the complete system works,” Prilutsky said. “That’s one of the reasons this study was done, so we could understand how the spinal network coordinates limb movement and develop a realistic computational model of spinal motor control. This will help us better understand how the spinal cord controls movement.”