Dr. Vincent Cheung has spent countless hours in the laboratory working with frogs, making jumps, leaps and hops in understanding the human brain. He has been determining how frogs’ brains control their muscles and is now using his findings to help stroke survivors with rehabilitation.

There are many ways frogs can move—they can jump, walk, kick, and swim. “They can also wipe off irritants,” he said as he stood up, mentally transformed into a frog, and made sweeping motions with his leg. He attempted to twist his legs in impossible ways, showing how frogs crawl, kick to defend themselves, and swim what humans call the “frog stroke.” Perhaps the expression “You are what you study” has some truth. Fortunately, before a permanent metamorphosis, scientific passion acted as a princess’s kiss, transforming him back into a researcher eager to explain the mechanics behind muscle activity.

Frogs offer an ideal model through which to study motion. The flexibility needed to allow their legs to perform such diverse actions requires complex coordination similar to the intricacy required for human movement. Thus, what we learn from these amphibians may also be applied to humans. Cheung, a research scientist at the McGovern Institute for Brain Research at the Massachusetts Institute of Technology and a collaborating scientist in the Motor Analysis Laboratory at Harvard Medical School, is interested in the human motor system and how our brain learns and adapts to new muscle movements. He seeks to answer a difficult question that scientists for have been working on for decades—how the brain is capable of handling a wide range of movements simultaneously.

The 600-plus muscles in the human body lead to an impressive number of possible combinations of muscle contractions and relaxations. “It’s like how there are 26 letters in the alphabet, but millions of words,” Cheung says. In order to handle all of these combinations, the brain must have a strategy. The brain’s method is to group muscles together, forming a “synergy,” and then to activate them as a unit. To evaluate how rigid synergies are, Cheung disrupted the nervous system of frogs by destroying certain nerve cells and then assessed how the disruption affected the frogs’ muscle synergies. Through quantitative analysis of electrical activity of the muscles, he found that the synergies mostly stayed intact. Thus, synergies are generally independent and can function normally even under altered conditions. He hopes to apply this knowledge to develop novel rehabilitation techniques.

Cheung has worked with muscle synergies for many years since completing his bachelor’s degree at the University of British Columbia in both mathematics and pharmacology and therapeutics. He was then admitted to the Harvard-MIT Division of Health Sciences and Technology where he worked with his advisor, Emilio Bizzi, to complete his PhD dissertation on the modulation of muscle synergies for motor adaptation.

Bizzi’s first impression of Cheung was that he was a very serious person. Gradually, this opinion changed as he began to learn more about his advisee’s personal interests. “I was always fascinated by him,” Bizzi said. One day Bizzi went to retrieve his mail and was confused when he saw that there were two copies of his subscription to the New York Times Book Reviews instead of the usual one. He was surprised and impressed when he realized that the other was addressed to Cheung. Soon after, he also learned of Cheung’s musical talents (even attending many of his concerts), which earned Cheung a diploma in Piano Performance from the Royal Schools of Music in London, and extensive knowledge of Western and Asian culture, particularly of China’s fine arts and history. “Immediately, I understood that Vincent is a cultivated humanist, a cultivated person,” he said. Indeed, Cheung is well rounded, knowledgeable in the humanities, arts and sciences. He believes that neuroscience is like philosophy and that “understanding how we move is a way to understand life.”

Since initially joining Bizzi’s lab, Cheung has progressed from experimenting with frogs to working with human stroke survivors and has applied what he has learned from his previous projects to try to improve rehabilitation techniques. Together, Cheung and Bizzi hope to determine how the brain controls muscle synergies and whether or not this arrangement is changed when a person experiences a stroke.

A stroke occurs when blood flow to an area of the brain is blocked and causes the brain cells in that region to die. After collecting information on many stroke survivors, with different levels of impairment, Cheung was able to categorize most patients into three groups: the mildly impaired, the fairly impaired, and the chronically impaired. After analyzing persons in the first category, the mildly impaired, he found that synergies were not much different from those in a healthy person. The groups of muscles were preserved; only the activation of them was changed. However, the synergies in the fairly impaired were different. Some muscle synergies were merged together, leading to a loss of complexity, which explained the patients’ stiffer movements and reduced range of motion. Even more affected were those belonging to the chronically impaired category. Patients in this group had had their strokes long ago and had experienced more extensive brain damage, and thus their motor skills were more limited than those of the fairly impaired.. Cheung found that the synergies in these patients were actually fractured; the greater complexity of synergies made it harder for their brains to function efficiently and effectively.

He interprets the modification of muscle synergies as the brain’s way of adapting to damage and hopes that by understanding how synergies were altered he can discover how to change them back. Then, rehabilitation could help patients relearn their prior motor function with their original synergies. Ideally, individualized and effective rehabilitation methods can be implemented for severe injury survivors.

Cheung and Bizzi are planning to implement a project with the MIT gymnastics team in a few months by evaluating how gymnasts learn various new techniques with mobile sensors that will be able to determine changes in muscle activity. Electrodes will be attached to the skin on their limbs above muscles to measure activity through electromyography, a technique that detects and records skeletal muscle activity. They expect to find that the acquisition of new skills will cause the brain to adapt by developing more synergies alongside existing ones. If successful, the two plan to use this information to understand how the brain learns new things and hope to apply their findings to help stroke patients regain normal function by relearning their past abilities.

Cheung’s passion for his research ensures that he will continue to be invested in it, even after almost a decade of work on muscle synergies, and will hopefully lead him to more discoveries. Where will he be in five or ten years? His advisor avowed, “a leader in the field of motor control.”