Cats always land on their feet, but what makes them so mobile? Their unique sense of balance has more in common with humans than it might seem. Researchers at the Georgia Institute of Technology are studying feline locomotion to better understand how the spinal cord works to help humans with partial spinal cord damage walk and maintain balance.
Using a combination of experimental studies and computational models, the researchers showed that somatosensory feedback, or nerve signals from specialized sensors throughout a cat’s body, help inform the spinal cord of continuous movement and coordination of all four limbs to prevent cats from falling when they encounter obstacles. Research indicates that by using those sensory cues related to movement, an animal can walk even if the connection between the spinal cord and the brain is partially broken.
Understanding the mechanics of this type of balance control is especially important for older adults who often have balance problems and can injure themselves if they fall. Ultimately, the researchers hope that this will lead to a new understanding of the role of somatosensory feedback in controlling balance. It could also lead to advances in the treatment of spinal cord injury because research indicates that activating somatosensory neurons can improve the function of spinal neural networks below the site of spinal cord damage.
We were interested in the mechanisms that make it possible to reactivate injured networks in the spinal cord. We know from previous studies that somatosensory feedback from moving legs helps activate the spinal networks that control movement, enabling stable locomotion.
Boris Prilutsky, Professor, Faculty of Biological Sciences
The researchers presented their findings in the journal “Sensory Disorders from Cutaneous Handlimb Effects Generate Coordinated Functional Responses in All Four Limbs During Locomotion in Healthy Cats.” eNeuro.
Although transgenic mouse models have recently become dominant in neural control in locomotion research, the cat model provides an important advantage. When they move, the mice remain crouched, which means they are less likely to have balance problems even if somatosensory feedback fails. On the other hand, humans and cats cannot maintain balance or even move if they have lost sensory information about limb movement. This indicates that larger species, such as cats and humans, may have a different organization of the spinal neural network that controls locomotion compared to rodents.
Georgia Tech has partnered with researchers at the University of Sherbrooke in Canada and Drexel University in Philadelphia to better understand how signals from sensory neurons coordinate the movements of all four legs. Sherbrooke’s lab trained cats to walk on a treadmill at a pace consistent with a human’s gait and then used electrodes to stimulate their sensory nerves.
The researchers focused on the sensory nerve, which transmits the sense of touch from the top of the foot to the spinal cord. By electrically stimulating this nerve, the researchers mimicked hitting an obstacle and saw how the cats stumbled and corrected their movement in response. Stimulation was applied at four periods of the gait cycle: mid-position transition, stance-to-swing transition, mid-swing, and swing-to-stand transition. From this, they learned that the middle swing period and the transition from standing to swing were the most significant periods because the stimulation increased the activity of the muscles that flex the knee and hip joints, joint flexion and toe height, stride length, and stride duration. motivating party.
“In order to maintain balance, the animal must coordinate the movement of the other three limbs, otherwise it will fall,” Prilutsky said. “We found that stimulating this nerve during the swinging phase increases the duration of the standing phase of the other limbs and improves stability.”
In fact, when the cat stumbles during the swinging phase, the sensation triggers reflexes in the spine that ensure that the other three limbs stay on the ground and keep the cat upright and balanced, while the swinging limb goes over the obstacle.
Through 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 control systems. The data collected is used to calculate somatosensory signals related to the length, speed, and force produced by the muscles, as well as the pressure on the skin on all extremities. This information forms motion sensations in the animal’s spinal cord and contributes to coordination between the limbs through neural networks in the spine.
“To help treat any disease, we need to understand how the proper system works,” Prilutsky said. “This was one of the reasons for conducting this study, so that we can understand how spinal networks coordinate limb movements and develop a realistic computational model for controlling movement of the spine. This will help us to better understand how the spinal cord controls movement.”
Merlette, AN, et al. (2022) Sensory disturbances from cutaneous effects of Hindlimb generate coordinated functional responses in all four limbs during locomotion in healthy cats. eNeuro. doi.org/10.1523/ENEURO.0178-22.2022.