Stanford Study of Owls Finds Link in Brain between Sight and Sound

STANFORD, Calif.--(BUSINESS WIRE)--Jan. 18, 2006--Just imagine
listening to someone talk and also hearing the buzz of the overhead
lights, the hum of your computer and the muffled conversation down the
hallway. To focus on the person speaking to you, your brain clearly
can't give equal weight to all incoming sensory information. It has to
attend to what is important and ignore the rest.


Two scientists at the Stanford University School of Medicine have
taken a big step toward sorting out how the brain accomplishes this
task. In the Jan. 19 issue of Nature, the researchers show that a
mechanism for prioritizing information -- previously reported only in
primates -- is also used by birds.

"What our experiment demonstrates is a fundamental principle of how
the brain pays attention," said the paper's senior author, Eric
Knudsen, PhD, the Edward C. and Amy H. Sewall Professor of
Neurobiology. "The promise here is that because we are doing this in
owls, we can get at the mechanisms of how this works."

The study determined that the circuits in the brain that process
auditory information are influenced powerfully by the circuits that
control where the animal is looking -- the animal's direction of gaze.

"The ability to hear and the direction of gaze aren't necessarily
linked," said the paper's first author, postdoctoral scholar Daniel
Winkowski, PhD. Sounds originating from any direction don't require
visualization to be heard. "It's exciting to find that the circuits in
the brain that control gaze direction affect how the brain processes
auditory information," he added.

With funds from the National Institutes of Health, Winkowski and
Knudsen used electrodes to stimulate the area of the brain responsible
for controlling the direction of gaze in barn owls, and then studied
how that affected the neural responses in regions of the brain that
process auditory information. When the gaze control circuit was
activated, they found that the owls' auditory system responded more
strongly and more selectively to sounds that came from the same
spatial location as that encoded by the stimulated site. The same
stimulation suppressed the auditory system's response to sounds coming
from other locations.

Selecting certain kinds of information to be processed, while ignoring
others, is the root of attention. What was previously known about the
mechanism of attention was based on research done by other scientists
-- including assistant professor of neurobiology Tirin Moore, PhD --
who have looked at how monkeys focus their attention on things they
see. These researchers have found that when a monkey decides to turn
its eyes, the regions of the brain that process visual information
increase their responses to objects that the monkey is about to look
at and decrease their responses to all other objects in the world.

Finding that auditory responses can be regulated by the circuits that
control gaze in barn owls suggests that the brain uses a common
strategy to focus attention that spans different types of animals and
different parts of the brain.

"This paper opens the floodgates for studying a wide range of
species," Knudsen said. "The fundamental mechanisms are probably going
to be the same in all vertebrates, as even frogs and fish have gaze
control." All animals have to be able to attend to certain stimuli and
ignore others.

"Now that we have found that the principle applies in owls as well as
monkeys, we can figure out the mechanisms of how the brain manages
attention," said Winkowski. In owls, the circuits being examined are
amenable to manipulations that will allow researchers to determine
what mechanisms are involved and which neurotransmitters and
neurotransmitter receptors are used in signaling attention.

"Relatively nothing is known about how the brain increases and
decreases signaling," Winkowski said. "We want to discover the
cellular mechanisms of how attention works."

"Once we learn the circuitry for attention, we plan to use that to
drive learning in an efficient way," said Knudsen. He added that they
eventually hope to show that they can make adjustments in the circuits
of the owls' brains that will lead to improved performance in the owl.

Understanding the mechanisms of attention naturally leads to the
possibility of applying their knowledge to human disorders of
attention, learning and schizophrenia. "If you understand
mechanistically how something works, then you will know how best to
fix it," said Knudsen. "It's like with a car; if you know in detail
how it is built, then you can fix anything that goes wrong with it."

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education and patient care at its three institutions -- Stanford
University School of Medicine, Stanford Hospital & Clinics and Lucile
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Public Affairs at http://mednews.stanford.edu.