MR Shows How Brain Changes Focus to Track Objects

When searching for a child lost in a crowd, this means that the brain areas usually focused on recognizing other objects such as animals, or even the areas controlling abstract thought, change their focus, and join the search party. Therefore, the brain rapidly switches into a highly focused child-finder, and redirects resources it uses for other mental tasks.

“Our results show that our brains are much more dynamic than previously thought, rapidly reallocating resources based on behavioral demands, and optimizing our performance by increasing the precision with which we can perform relevant tasks,” said Tolga Cukur, a postdoctoral researcher in neuroscience at the University of California (UC), Berkeley (USA), and lead author of the study published April 21, 2013, in the journal Nature Neuroscience. “As you plan your day at work, for example, more of the brain is devoted to processing time, tasks, goals, and rewards, and as you search for your cat, more of the brain becomes involved in recognition of animals,” he added.

The findings help clarify why people find it difficult to concentrate on more than one task at a time. The study also provides clues into how individuals are able to shift their attention to challenging tasks, and may provide greater insight into neurobehavioral and attention deficit disorders such as attention deficit-hyperactivity disorder (ADHD).

These results were obtained in studies that used functional magnetic resonance imaging (fMRI) to record the brain activity of study participants as they searched for individuals or vehicles in movie clips. In one experiment, participants held down a button whenever an individual appeared in the movie. In another, they did the same with vehicles.

The brain scans simultaneously measured neural activity through the blood flow in thousands of locations across the brain. Researchers used regularized linear regression analysis, which finds data correlations to build models showing how each of the about 50,000 sites close to the cortex responded to each of the 935 classifications of actions or objects seen in the movie clips. Next, they compared how much of the cortex was focused on detecting humans or vehicles depending on whether or not each of those categories was the search target.

When searching for a human, more parts of the brain are engaged. The investigators discovered that when participants searched for humans, comparatively more of the cortex was devoted to humans, and when they searched for vehicles, more of the cortex was devoted to vehicles. For example, areas that were typically involved in recognizing specific visual categories such as plants or buildings changed to become attuned to humans or vehicles, vastly expanding the area of the brain occupied in the search. “These changes occur across many brain regions, not only those devoted to vision. In fact, the largest changes are seen in the prefrontal cortex, which is usually thought to be involved in abstract thought, long-term planning, and other complex mental tasks,” Dr. Cukur said.

The findings add onto an earlier UC Berkeley brain imaging study that demonstrated how the brain organizes thousands of animate and inanimate objects into what researchers call a “continuous semantic space.” Those findings questioned earlier suppositions that every visual category is represented in a separate region of the visual cortex. Instead, researchers found that categories are in reality represented in highly organized, continuous maps.

The latest study additionally shows how the brain’s semantic space is distorted during a visual search, depending on the search target. The investigators have posted their findings in an interactive, online brain viewer.

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University of California, Berkeley