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How the Brain Orchestrates Reaching and Walking

The events in the brain and nervous system that allow a person to reach for a cup of coffee—and pick it up—is viewed differently by a neuroscientist and an engineer. Yet scientists from both groups came together to collaborate on a KDI-funded project that examined just how the cerebellum—the part of the brain that coordinates muscle activity—functions in overseeing the volitional muscle activity of the human body.

The project was called Artificial Implementation of Cerebro-Cerebellar Control of Reaching and Walking. The principal investigator was Dr. Steve Massaquoi of the Massachusetts Institute of Technology (MIT). Dr. Massaquoi and other engineers from MIT collaborated with Dr. Timothy Ebner, a neuroscientist who is professor and head of the Department of Neuroscience at the University of Minnesota.

The team studied several existing models of cerebellar function. According to Dr. Ebner, "Many experts believe the cerebellum does its business by carrying what we call an internal model, a kind of map or schematic diagram of the body and how that body works, or should work." By this view, the cerebellum holds the internal model, using it as a template for reference.

"But," according to Dr. Ebner, "Steve Massaquoi thinks that view is incorrect and that movement control is achieved through a more traditional engineering model applied to physiology, where the brain processes control signals using normal feedback loops." The question, then, is whether the cerebellum is a kind of "stationmaster" for neural messages moving to and from the muscles of the body, or if movement is coordinated and controlled on the basis of an internal schema of the body's circuitry.

Dr. Ebner collected basic data by recording the cerebellar activity of monkeys who had been trained to do certain tasks. As the monkeys reached, grasped, and performed other movements, Dr. Ebner and his colleagues recorded single-cell activity in the monkeys' cerebelli using microelectrodes. "Then we took those signals and processed them and tried to understand how information is represented and whether it matches either the internal map thesis or the signal-feedback theory," says Dr. Ebner.

Ultimately, the researchers found that the microelectrode signals were consistent with a traditional engineering signal-feedback model of neurological activity, garnering insights along the way into how the cerebellum handles information about speed, direction, and velocity of movement.

Although the team’s findings are preliminary, practical applications are already emerging. Better insight into how the brain controls movement will help engineers develop control systems that will improve robots and robotic movement. The KDI team’s work is also directly relevant to the study of neural control signaling and applications in the development of assistive devices for people with spinal cord and other devastating neurological injuries. And the same data promise to help in the design of computer interfaces.

Beyond applications in bioengineering, the KDI team’s research will help medical researchers better understand cerebellar disease. According to Dr. Ebner, "If we can understand what the cerebellum does and better understand some of these control signals, it becomes easier to have some insight into the processes of cerebellar diseases—why, for example, these diseases affect walking and talking."

"As exciting as these applications are," says Dr. Ebner, "it's equally important that people like the MIT engineers on our project—specialists in control theory and engineering design—got a real sense of biology, of neural signals and what a mess they really are. There's a point where an engineer begins to wonder how this human brain can ever work. At the same time, the biologically oriented team members have had much greater exposures to the math-based world of engineering. We've had the rare opportunity to reformulate our thinking on the basis of concepts we might normally have never been exposed to. This is what made the project an exceptionally valuable experience."

Dr. Ebner adds, "Neuroscience really needs the insight of the engineers and the computational people because the human nervous system is incredibly complex and still, in many ways, a mystery. Collaborating and having the cross-fertilization from different perspectives offer a great number of tools that help us move forward."

For more information on Dr. Ebner’s work, visit his Web page.

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