It can be a wobbly world for older people and those with lower limb prostheses or nervous system disorders. Dr. Daniel Ferris, the Robert W. Adenbaum Professor & Senior Associate Chair, at the J. Crayton Pruitt Family Department of Biomedical Engineering in the UF Herbert Wertheim College of Engineering, has been working to mitigate this problem. He and Steven Peterson, a Ph.D. student at the University of Michigan – Ann Arbor, have just published two papers that examine the neural mechanisms for human balance and motor coordination.
The first paper, which has already appeared online and in eNeuro, published the results of research that studied physical perturbation (movement of the body) vs. visual perturbation (movement of the eyes only) to see how the brain responds to different types of perturbations. Knowing how the brain responds helps determine what interventions might succeed in improving balance.
The second paper, published in the Journal of Neurophysiology, showed the results of a subsequent study on the use of Virtual Reality (VR) headsets in training people to improve balance.
Losing balance
Looking to answer the question, “Why, as we get older, do we have more problems with balance?” Ferris and Peterson first determined “When do you lose your balance? When does your brain detect it, and when do you respond?” In 2013, they built a balance beam that works on a treadmill. Using Dr. Ferris’ system for mobile brain imaging, they identified places in the brain that are involved in balance. “The brain knows about one second before it happens, that you are going to lose your balance,” Dr. Ferris said. “The left sensorimotor cortex is the first part of the brain that responds when you lose your balance and begin to fall.”
What part of the brain needs to be trained?
In the next phase of their research into helping people with balance problems, Ferris and Peterson asked, “How can we train people who have bad balance – elderly people, amputees, stroke, or spinal cord injury – to improve their balance?” Earlier theories suggested that physical perturbation (pushing and pulling the body) could provide a response that would help people get better at keeping their balance. Following people in the real world revealed that people usually fall without anyone or anything pushing into them. This suggests that pushing and pulling may not be the best means of training balance.
Ferris and Peterson’s study compared two forms of perturbation – physical (push and pull) and visual (wearing a virtual reality headset that incorporates visual perturbation). Using mobile brain imaging, which allows subjects to move around while brain activity is being measured, they found some interesting information about different areas of the brain:
• The anterior cingulate responds to error monitoring, as experienced in physical perturbation; but visual perturbation does not cause a response in the anterior cingulate.
• The left sensorimotor cortex shows a response to physical perturbation but not visual perturbation.
• The occipital region of the brain (the area that responds to vision), as expected, responded to visual perturbation.
• The posterior parietal region (where limb coordination is centered) has a strong response to visual perturbation; physical perturbation does not excite much of a response.
Ferris and Peterson reached the conclusion that visual perturbation primes the area responsible for coordination that is also important for motor learning. Therefore, visual perturbation should help subjects train their minds to better balance their bodies. They reported these findings in eNeuro: “Differentiation in Theta and Beta Electrocortical Activity between Visual and Physical Perturbations to Walking and Standing Balance.”
What is the best way to train the posterior parietal area?
If visual perturbation is better at stimulating the posterior parietal area of the brain where much of coordination is centered, it should help subjects learn to maintain better balance. The research team designed an experiment to test this hypothesis, using young adults without any balance problems.
To typify traditional balance training, Ferris and Peterson once again used their balance beam built into a treadmill. They tested two groups to determine if visual perturbation during training could make a significant difference in maintaining balance:
• One group who trained by walking on the balance beam while wearing a virtual reality headset (VR) without any perturbation
• One group who trained by walking on the balance beam while wearing a virtual reality headset (VR) that caused a visual perturbation (a 20-degree tilt in the field of vision) for one in every 10 seconds
Groups with perturbations and without visual perturbations had exactly the same “errors” introduced during training to give a controlled level of difficulty to the training.
Post-training testing for balance showed that the balance of the group of people who trained with VR without visual perturbations improved their balance by about 10%. The group who trained with VR that included visual perturbations improved their balance by about 40%.
Results showed conclusively that adding visual perturbations improved the outcome of balance training. Ferris and Peterson published this study in The Journal of Neurophysiology: “Transient visual perturbations boost short-term balance learning in virtual reality by modulating electrocortical activity.”
Ferris concluded, “We have made two important discoveries in our research. Visual perturbation can aid in training the mind to balance the body, and virtual reality headsets provide a means to enable this training. There is more work to do, but we have made an excellent start.”