Separate brain regions firing in unison may be what keeps us focused on important things while we ignore distractions.

A deluge of visual information hits our eyes every second, yet we're able to focus on the minuscule fraction that's relevant to our goals. When we try to find our way through an unfamiliar area of town, for example, we manage to ignore the foliage, litter and strolling pedestrians, and focus our attention on the street signs.

Now, researchers at the Massachusetts Institute of Technology have discovered that the brain's control center syncs up to its visual center with high-frequency brain waves, directing attention to select features of the visual world.

"It's been known that the prefrontal cortex plays an important role in focusing our attention, but the mystery was how," said neuroscientist Robert Desimone, who led the study, published in *Science *Friday. "Now we have some insight into how it has that focusing role — through this synchrony with our sensory systems."

This novel understanding of attention may inform future studies on disorders like schizophrenia and ADHD, in which patients are easily distracted and the prefrontal cortex is thought to be impaired. The region's newly discovered role as a source of synchronized brain activity may be crucial to understanding these diseases.

Previous research showed that when something important (such as a street sign) catches our attention, the sign-processing neurons in the visual region begin to fire in unison. The rest of the neurons in the region fire too, stimulated by other information that hits the eye, but they chatter out of sync with one another. The synchronized firing of neurons carrying the important aspects of the visual field is thought to focus our attention to these features.

"If there's a group of people that's chanting in the middle of a large crowd having random conversations, the chanters stand out," Desimone said.

What wasn't known is what gets the chanters going in the first place. Neuroscientists knew the control center, known as the prefrontal cortex, was involved, but it is on the opposite side of the brain from the visual center, so it was unclear how such long-range interactions might actually operate.

First, Desimone's team recorded the activity of neurons in two monkeys while the animals focused on images on a computer screen. They found that, as expected, neurons in the visual area began firing together when the monkeys looked at the images. But they discovered that neurons in a region of the prefrontal cortex were also firing in unison, and at the same frequency as those in the visual area.

When they took a closer look at their data, they found that the prefrontal region started firing 80 milliseconds after the monkeys were cued to focus on the image, while the visual cortex started firing after 130 milliseconds. The two regions, on opposite sides of the brain, then fired at a high frequency in synchrony with one another. The waves were offset by 8 to 13 milliseconds, which the authors believe may be the time it takes for a signal to travel between the two regions.

"Imagine a spring between your two hands, and you're vibrating your hands back and forth," said Desimone. "If you time it just right, your hands are going to have a spring bouncing back and forth at a certain resonance. The neural equivalent of that is a very strong signal in the brain."

Neurons in the prefrontal cortex were essentially directing the neurons in the visual cortex to pay attention by firing with them, Desimone said. He believes this type of synchronization may be a mechanism for communication between separate brain regions.

"[The results] provide a possible explanation for how attention-dependent synchrony might be brought about by the [prefrontal cortex], and how the communication between distant neurons might be facilitated by attention," said Tirin Moore, a neurobiologist at Stanford University who was not involved with the study. "This is an important step indeed."

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*Citation: "High-Frequency, Long-Range Coupling Between Prefrontal and Visual Cortex During Attention," by G.G. Gregoriou, S.J. Gotts, H. Zhou, R. Desimone. Science Vol. 324, Issue 5930.

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Image: Flickr/Quasic