CAMBRIDGE, MA -- APRIL 21, 2005 -- At any given moment, the world bombards the senses with more information than the brain can process, and for more than a century scientists and psychologists have debated how the brain filters out distractions and focuses attention on the things that matter. Using the visual system as a model, Robert Desimone of the McGovern Institute for Brain Research at MIT and his former colleagues at the National Institutes of Health show that neurons synchronize their signals to command attention, like a chorus rising above the din of noisy chatter in a crowded room.

-- Robert Desimone, Director of the McGovern Institute, Offers New Findings On How the Brain Filters Out Distractions and Focuses Attention; Research Paper is Leading Article in Newest Edition of Science --

"We think that synchronizing signals could be a general way the brain focuses on what's important," says Desimone, the senior author of an April 22nd paper in Science. "Attention is a general problem for the brain, and maybe it has a general solution. "

This new study addresses a central question that anyone who has tackled a "Where's Waldo?" book can appreciate. When looking for Waldo on the crowded page, does the brain scan the page spatially (serial processing), like a mental spotlight moving across an otherwise dark page? Or does the brain take in the whole page at once and gradually zoom in on relevant features such as color and shape (parallel processing). In the first model, the attentional spotlight would track across the page, checking each detail against a mental image of Waldo's red stocking cap and striped shirt. In the second model, the color red and stocking-cap shapes would gradually come to the foreground and other shapes and colors recede.

For decades, scientists divided into two camps regarding these models, but recent evidence made some scientists suspect that the brain conducts a combination of the two. "What's cool about this paper is that it shows both processes are going on in the same chunk of the brain and in the same neurons," says Jeremy Wolfe, professor of Ophthalmology at Harvard Medical School, who wrote an accompanying review article in Science.

To explore visual attention, researchers study macaque monkeys, recording the activity of specific neurons, along with the eye movements, while the monkeys scan a complex array in an experimental equivalent of looking for Waldo. The neurons belong to the V4 area, a mid-region of the visual cortex known to be important to attention. Neurons specialize as to what they detect best. A "red" neuron gives off a stronger signal when red appears in the field of view, and the signal is even stronger if the monkey is actively searching for red. Moreover, if the monkey is searching for a red object, red neurons turn up their activity before the eyes even move towards the red item, as if the louder signal were calling: Look over here! "We think the yelling neurons are commanding the eyes to move towards a feature that matches something in the mental image," Desimone says.

Even so, the ability of a neuron to raise its lone voice does not explain how it gets heard over the cacophony of all the other neurons. "We think it's not just a question of the individual neuron," he says. "It's how it cooperates with other neurons to make their voices heard. We showed that to increase the signal, the neurons synchronize their activity." Desimone uses the analogy of a room full of people talking. If random individuals raise their voices, the room just gets louder. If a group of people starts chanting in unison, their voices rise above the background noise. Synchronization of the signals helps explain how the brain uses parallel processing to concentrate on relevant features in a complex scene. Then the brain switches to serial processing, scrutinizing relevant objects sequentially to find the object of desire.

"If timing is important for visual attention and this is the way the brain focuses," reflects Desimone, "that exploration might open up whole new domains for understanding and possibly treating attention disorders, which are common in mental illnesses, including ADHD and even schizophrenia."

"This is a unique finding," comments Richard Andersen, a neurophysiologist studying the visual system at the California Institute of Technology. "Knowing how the human brain processes visual information," say Andersen and Wolfe, "might also help engineers design better instrumentation and equipment for important visual search tasks like airport baggage screening or mammography."

The study was funded by the National Institute of Mental Health. The research began while Desimone, who is now the Director of the McGovern Institute for Brain Research at MIT, was Scientific Director of the Intramural Research Program of the National Institutes of Mental Health.

About the McGovern Institute at MIT

The McGovern Institute at MIT is a research and teaching institute committed to advancing human understanding and communications. Led by a team of world-renowned, multi-disciplinary scientists, The McGovern Institute was established in February 2000 by Lore Harp McGovern and Patrick McGovern to meet one of the great challenges of modern science - the development of a deep understanding of thought and emotion in terms of their realization in the human brain. Additional information is available at: http://web.mit.edu/mcgovern/

Lyn Chamberlin
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