Newswise — Cats always land on their feet, but what makes them so nimble? Their unique sense of balance has more in common with humans than meets the eye. Georgia Institute of Technology researchers are studying cat locomotion to better understand how the spinal cord works to help humans with partial spinal cord injuries walk and maintain balance.
Using a mix of experimental studies and computational models, the researchers show that somatosensory feedback, or neural signals from specialized sensors throughout a cat’s body, help inform the spinal cord of movement taking place and coordinate the four limbs to prevent the cats from falling when they encounter obstacles. Research suggests that with these movement-related sensory signals, the animal can walk even if the connection between the spinal cord and the brain is partially fractured.
Understanding the mechanisms of this type of balance control is particularly relevant for older people who often have balance problems and can be injured in falls. Ultimately, the researchers hope this could provide new understanding of the role of somatosensory feedback in balance control. It could also lead to advances in the treatment of spinal cord injuries, as research suggests that activating somatosensory neurons can improve the function of spinal neural networks below the site of spinal cord injury.
“We were interested in the mechanisms that allow damaged networks to be reactivated in the spinal cord,” said Professor of the School of Biological Sciences Boris Prilutsky. “We know from previous studies that somatosensory feedback from moving legs helps activate spinal networks that control locomotion, enabling stable movement.”
The researchers presented their findings in “Sensory Perturbations From Hindlimb Cutaneous Afferents Generate Coordinated Functional Responses in All Four Limbs during Locomotion in Intact Cats” in the journal in Euro.
Although genetically modified mouse models have recently become dominant in neural control of locomotion research, the cat model offers an important advantage. When moving, the mice remain crouched, which means they are less likely to have 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 organization of the spinal neural network controlling locomotion than rodents.
Georgia Tech has teamed up with researchers from 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. The Sherbrooke lab trained cats to walk on a treadmill at a pace consistent with human gait, then used electrodes to stimulate their sensory nerve.
The researchers focused on the sensory nerve that transmits tactile sensation from the top of the foot to the spinal cord. By electrically stimulating this nerve, the researchers mimicked hitting an obstacle and saw how cats stumbled and corrected their movement in response. Stimulations were applied to four periods of the gait cycle: mid-stance, stance-to-wobble transition, mid-wobble, and wobble-to-stance transition. From there, they learned that the middle of the swing and the transition from stance to swing were the most important times because stimulation increased activity in the muscles that flex the knee and hip joints, flexing the joints and toe height, step length and step duration. the stimulated member.
“In order to maintain balance, the animal must coordinate the movement of the other three limbs, otherwise it would fall,” Prilutsky said. “We found that stimulating this nerve during the swing phase increases the stance phase duration of other limbs and improves stability.”
This is because when the cat stumbles during the swing phase, the sensation triggers spinal reflexes that ensure the other three limbs stay on the ground and keep the cat upright and balanced, while the swing limb straddles the obstacle. .
With these Canadian lab experiments, researchers at Georgia Tech and Drexel University are using observations to develop a computer model of the cat’s musculoskeletal and spinal neural control systems. The data collected is used to calculate somatosensory signals related to muscle length, speed and force produced, as well as pressure on the skin of all limbs. This information forms sensations of movement in the animal’s spinal cord and contributes to coordination between limbs through spinal neural networks.
“To help treat any disease, we need to understand how the intact system works,” Prilutsky said. “This is one of the reasons this study was done, so that we can understand how spinal networks coordinate limb movements and develop a realistic computer model of spinal control of locomotion. This will help us better understand how the spinal cord controls locomotion.
CITATION: Merlet AN, Jéhannin P, Mari S, Lecomte CG, Audet J, Harnie J, Rybak IA, Prilutsky BI, Frigon A (2022) Sensory Perturbations from Hindlimb Cutaneous Afferents Generate Coordinated Functional Responses in All Four Limbs during Locomotion in Intact Cats . eNeuro 9: 0178-22.
The Georgia Institute of Technology, or Georgia Tech, is one of the top public research universities in the United States, developing leaders who advance technology and improve the human condition. The Institute offers degrees in business, computer science, design, engineering, liberal arts, and science. Its more than 46,000 students, representing 50 states and more than 150 countries, study at the main campus in Atlanta, at campuses in France and China, and through distance and online learning. As a leading technology university, Georgia Tech is an engine of economic development for Georgia, the Southeast, and the country, conducting more than $1 billion in research annually for government, industry, and the society.