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Source: University of California - San Francisco
Date Posted:2005-09-23
Web Address:http://www.sciencedaily.com/releases/2005/09/050923075201.htm

'NOISE' AFFECTS HOW BRAIN DIRECTS BODY TO MOVE


A UCSF study has revealed new information about how the brain directs
the body to make movements. The key factor is "noise" in the brain's
signaling, and it helps explain why all movement is not carried out
with the same level of precision.
Understanding where noise arises in the brain has implications for
advancing research in neuromotor control and in developing therapies
for disorders where control is impaired, such as Parkinson's disease.
The new study was developed "to understand the brain machinery
behind such common movements as typing, walking through a doorway or
just pointing at an object," says Stephen Lisberger, PhD, senior study
investigator who is director of the W.M. Keck Center for Integrative
Neuroscience at the University of California, San Francisco.
Study co-investigators are Leslie C. Osborne, PhD, a
postdoctoral fellow at UCSF, and William Bialek, PhD, professor of
physics at Princeton University.

The study findings, reported in the September 15 issue of the
journal Nature, are part of ongoing research by Lisberger and
colleagues on the neural mechanisms that allow the brain to learn and
maintain skills and behavior. These basic functions are carried out
through the coordination of different nerve cells within the brain's
neural circuits.

"To make a movement, the brain takes the electrical activity of
many neurons and combines them to make muscle contractions," Lisberger
explains. "But the movements aren't always perfect. So we asked, what
gets in the way?"
The answer, he says, is "noise," which is defined as the
difference between what is actually occurring and what the brain
perceives. He offers making a foul shot in basketball as an example. If
there were no noise in the neuromotor system, a player would be able to
perform the same motion over and over and never miss a shot. But noise
prevents even the best players in the NBA from having perfect
foul-shooting percentages, he says.
"Neuroscientists are interested in what limits virtuosity. Our
finding is significant because it demonstrates that errors in what is
seen can have a bigger impact on motor performance than errors in
controlling muscles," says co-investigator Osborne, who conducted the
research.

"By studying how the brain reduces noise, we can learn more
about how it processes sensory inputs, makes decisions and executes
them. Understanding how noise is reduced to very precise commands helps
us understand how those commands are created," adds Lisberger, who also
is a Howard Hughes Medical Institute investigator and a UCSF professor
of physiology.
In the study, the research team focused on a movement that all
primates, including humans, are very skilled at: an eye movement known
as "smooth pursuit" that allows the eyes to track a moving target.
In a series of exercises with rhesus monkeys in which the
animals would fixate on and track visual targets, the researchers
measured neural activity and smooth pursuit eye movements. From this
data, the team analyzed the difference between how accurately the
animals actually tracked a moving object and how accurately the brain
perceived the trajectory.

Findings showed that both the smooth pursuit system and the brain's perceptual system were nearly equal.

"This teaches us that these very different neural processes are
limited to the same degree by the same noise sources," says Lisberger.
"And it shows that both processes are very good at reducing noise. The
differences that exist are likely caused by the separate parts of the
brain that are responsible for the separate processes."

He concludes, "Because the brain is noisy, our motor systems
don't always do what it tells us to. Making precise movements in the
face of this noise is a challenge. This study gives us new insights
into how the brain works to do that."


The research was supported by grants from the National Institutes of Health and the Howard Hughes Medical Institute.



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