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 coffeeand pick it upis 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 cerebellumthe part of the brain that coordinates muscle
activityfunctions in overseeing the volitional muscle activity of the
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 teams 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 teams 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
Beyond applications in bioengineering, the KDI teams
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 diseaseswhy, 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
projectspecialists in control theory and engineering designgot 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. Ebners work,
visit his Web
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