Study of Owls Finds Link in Brain Between Sight and Sound
Sight and Sound
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."