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For most people, balance is something they rarely think about. Standing upright, walking across a room, or navigating uneven ground happens almost automatically, guided by rapid, unconscious processes in the nervous system.

But for older adults, and especially those living with Parkinson’s disease, that automatic control can gradually fade away.

New research coauthored by 91ԭ�� Assistant Professor Aiden Payne is helping to explain why—and opening a path toward treatments that could restore automatic balance control rather than simply teaching people to compensate for losing it. 

Payne, whose background spans biomedical engineering, computational modeling, neuroscience and psychology, studies how the body maintains balance and what happens when that control starts to break down. His latest work shows a new model that can measure how different parts of the nervous system contribute to staying upright.

“Balance is surprisingly complex,” Payne said. “There are a lot of different things that can go wrong, and a lot of ways the body can compensate when they do.”

In young, healthy adults, balance is largely controlled by fast, involuntary processes in the brainstem. Sensory signals from the body are rapidly translated into muscle activity, allowing people to stay upright without conscious effort.

“You normally don’t have to think about your balance unless you’re in a new or challenging environment,” Payne explained.

But as we age, that changes. 

“Older adults often say they have to pay attention to their balance,” he said. “That’s a sign the system is becoming less automatic.”

In the past, researchers have tried to measure this shift by asking someone to maintain balance while performing a cognitive task, like counting backwards. If performance declines, it suggests their balance is relying on conscious effort.

According to Payne, though, the problem is that these methods are not precise.

“There are so many confounding factors. People vary widely in how they perform cognitive tasks, and how they divide their attention between tasks. This makes it hard to isolate what’s actually happening—and even harder to know whether an intervention is targeting the right neural circuits.”

To overcome those limitations, Payne and his collaborators took an engineering approach. 

“If you’re trying to balance a robot, you have to turn the motors on in a manner that is continuously proportional to errors from the desired upright position,” he said. “We applied that same logic to humans and find that the nervous system is essentially doing the same thing.”

The starting point, developed by Payne’s doctoral advisor Dr. Lena Ting at Emory University, was the insight that the nervous system automatically controls balance much like how an engineer would control a robot: by continuously producing forces to oppose a loss of balance. But when these forces are generated by the nervous system, there is a delay due to neural conduction and processing. 

Payne’s work helped to extend this framework by identifying a second wave of muscle activity that is essentially doing the same thing, but with a longer delay, coming from a neural circuit that passes through higher brain areas.

This finding was made possible by experiments in which Payne and colleagues suddenly destabilized participants to observe how the nervous system reacts. Those studies revealed a rapid, automatic response involving the brainstem and muscles. When the balance challenge became more severe, a second wave of activity followed, engaging higher brain regions and producing additional muscle responses.

Using sensors to track muscle activity, the researchers developed a computational model that can separate and quantify different “levels” of control, from fast, automatic responses in the brainstem to slower, compensatory responses driven by higher brain regions.

The result is a detailed picture of how balance is maintained and how it changes under stress.

“We can now explain about 90 percent of the variation in evoked muscle activity for balance recovery, millisecond by millisecond,” Payne said. “That level of precision just hasn’t been possible before.”

The team tested the model in younger adults, as well as older adults with and without Parkinson’s disease.

The findings, published in , revealed that older adults and people with Parkinson’s rely more on slower, less automatic levels of control even during relatively small balance disturbances - both the brain and muscles appeared to overreact when challenged.

The researchers also identified a key difference in how muscles behaved. When one muscle activated to help stabilize the body, the opposing muscle often tightened at the same time. While this may feel protective, it creates stiffness, making movement less efficient, and preventing dynamic balance recovery. Participants who showed more of this stiffness tended to perform worse on clinical measures of balance.

“We didn’t see a huge difference in how much people with vs. without Parkinson’s disease relied on non-automatic control,” Payne said. “But we did see that the way they compensate is different.”

He explained that people with and without Parkinson’s may both rely more on higher levels of control, but they do so in distinct ways that relate differently to clinical measures of balance and mobility, offering insight that could help explain why current treatments work well for some patients but not others.

One of the most important findings, Payne said, is that the compensation itself may be part of the problem.

“When people start to worry about their balance, they become more careful and that can make them feel safer in the moment,” he said. “But over time, it may actually contribute to a loss of function.”

The study suggests that the exaggerated muscle responses seen in older adults and people with Parkinson’s may actually make recovery from balance disturbances less effective. Rather than helping, these overreactions may be one reason fall risk increases with age and neurological disease.

According to Payne, many people begin compensating long before it’s truly necessary, shifting away from automatic control too early. That can create a cycle where the body relies more on conscious effort, making balance feel increasingly difficult and both physically and mentally exhausting.

“And it’s not just about falling,” Payne said. “Having to constantly pay attention to your balance is limiting. It affects your ability to engage with the world.”

By precisely measuring how different levels of the nervous system contribute to balance, researchers can begin to test which interventions target the right mechanisms and for whom. This approach may eventually have applications beyond research, one day potentially helping identify individuals at risk for balance problems before they start losing their independence.

“We can now determine whether someone has increased brain activity simply by assessing muscle activity after a balance disturbance,” Payne said. “That could give us a way to identify people earlier and intervene before they experience significant declines.”

Over the next five to 10 years, Payne hopes this work will lead to more personalized and effective treatments that restore the automatic nature of balance rather than simply teaching people to compensate.

“We’ve been missing a way to directly observe what’s happening in the nervous system,” he said. “Now that we can measure it, we can start to fix it.”