braking mechanisms in the brain

Stop Signs: Study Identifies 'Braking' Mechanism In The Brain
Science Daily - As wise as the counsel to "finish what you've started"
may be,
it is also sometimes critically important to do just the opposite --
stop. And
the ability to stop quickly, to either keep from gunning the gas when
a
pedestrian steps into your path or to bite your tongue mid-sentence
when the
subject of gossip suddenly comes into view, may depend on a few
"cables" in the
brain.

Researchers led by cognitive neuroscientist Adam Aron, an assistant
professor of
psychology at the University of California, San Diego, have found
white matter
tracts -- bundles of neurons, or "cables," forming direct, high-speed
connections, between distant regions of the brain -- that appear to
play a
significant role in the rapid control of behavior.

Published in the April 4 issue of the Journal of Neuroscience, the
study is the
first to identify these white matter tracts in humans, confirming
similar
findings in monkeys, and the first to relate them to the brain's
activity while
people voluntarily control their movements.

"Our results provide important information about the correspondence
between the
anatomy and the activity of control circuits in the brain," Aron said.
"We've
known for some time about key brain areas involved in controlling
behavior and
now we're learning how they're connected and how it is that the
information can
get from one place to the other really fast."

"The findings could be useful not only for understanding movement
control," Aron
said, "but also 'self-control' and how control functions are affected
in a range
of neuropsychiatric conditions such as addiction, Tourette's syndrome,
stuttering and Attention Deficit Hyperactivity Disorder."

To reveal the network, Aron and researchers from UCLA, Oxford
University and the
University of Arizona performed two types of neuroimaging scan on
healthy
volunteers.

They used diffusion-weighted MRI, in 10 subjects, to demonstrate the
"cables"
between distant regions of the brain known to be important for
control, and they
used functional MRI, in 15 other subjects, to show that these same
regions were
activated when participants stopped their responses on a simple
computerized
"go-stop" task.

One of the connected regions was the subthalamic nucleus, within the
deep-seated
midbrain, which is an interface with the motor system and can be
considered a
"stop button" or the brake itself. A second region was in the right
inferior
frontal cortex, a region near the temple, where the control signal to
put on the
brakes probably comes from.

"This begs the profound question," Aron said, "of where and how the
decision to
execute control arises."

While this remains a mystery, Aron noted that an additional,
intriguing finding
of the study was that the third connected node in the network was the
presupplementary motor area, which is at the top of the head, near the
front.
Prior research has implicated this area in sequencing and imagining
movements,
as well as monitoring for changes in the environment that might
conflict with
intended actions.

The braking network for movements may also be important for the
control of our
thoughts and emotions.

There is some evidence for this, Aron said, in the example of
Parkinson's
patients. In the advanced stages of disease, people can be completely
frozen in
their movements, because, it seems, their subthalamic nucleus, or stop
button,
is always "on." While electrode treatment of the area unfreezes the
patients'
motor system, it can also have the curious effect of disinhibiting
them in other
ways. In one case, an upstanding family man became manic and
hypersexual, and
suddenly began stealing money from his wife to pay for prostitutes.

Examples like these motivate Aron to investigate the generality of the
braking
mechanism.

"The study gives us new targets for studying how the brain relates to
behavior,
personality and genetics," Aron said. "Variability in the density and
thickness
of the 'cable' connections is probably influenced by genes, and it
would be
intriguing if these differences explained people's differing abilities
not only
to control the swing of a bat but also to control their temper."

Coauthors on the study are Tim E. Behrens and Steve Smith, of Oxford
University,
Michael J. Frank, of the University of Arizona, and Russell A.
Poldrack, of
UCLA.

The research was supported by a 21st Century Science Award from the
James S.
McDonnell Foundation and by the United Kingdom Medical Research
Council.

Source: University of California - San Diego
http://www.sciencedaily.com/releases/2007/04/070403184940.htm

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