Noise in the brain's signalling influencing how our bodies are directed to move

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Noise in the brain's signalling influencing how our bodies are

directed to move

http://www.medicalnewstoday.com/medicalnews.php?newsid=31074

24 Sep 2005

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 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 C. Osborne, PhD, a postdoctoral

fellow at UCSF, and 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 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 Medical Institute.

University of California - San Francisco

http://www.ucsf.edu