Brain Regions Synchronize Activity to Enable Attention

“We think the brain not only puts regions that facilitate attention on alert but also makes sure those regions have open lines for calling each other,” said first author Amy Daitch, a graduate student researcher from the Washington University School of Medicine in St. Louis (MO, USA).

The study’s findings were published ahead of print November 11, 2013, in the Proceedings of the National Academy of Sciences of the United States of America (PNAS). People who suffer from brain injuries or strokes frequently have difficulties paying attention and concentrating. “Attention deficits in brain injury have been thought of as a loss of the resources needed to concentrate on a task,” said senior author Maurizio Corbetta, MD, a professor of neurology. “However, this study shows that temporal alignment of responses in different brain areas is also a very important mechanism that contributes to attention and could be impaired by brain injury.”

Attention lets people disregard extraneous sensory stimuli, similar to a driver disregarding a ringing cell phone, and pay attention to important stimuli, like stepping onto the road in front of the car. To examine brain alterations linked to attention, the scientists employed grids of electrodes temporarily implanted onto the brains of patients with epilepsy. Co-senior author Eric Leuthardt, MD, associate professor of neurosurgery and bioengineering, uses the grids to map for surgical removal of brain tissues that contribute to uncontrollable seizures.

With patient permission, the grids also can allow Dr. Leuthardt’s lab to study human brain activity with a degree of detail unavailable with any other technology. Typically, Dr. Corbetta and his colleagues research attention using various forms of magnetic resonance imaging (MRI), which can identify changes in brain activity that occur every 2 to 3 seconds. However, with the grids in position, Drs. Corbetta and Leuthardt can study the changes that occur in milliseconds.

The scientists scanned the brains of seven epilepsy patients before grid implantation, using MRI to map regions known to contribute to attention. With the grids in position, the investigators monitored brain cells as the patients watched for visual targets, directing their attention to different locations on a computer screen without moving their eyes. When patients saw the targets, they pressed a button to let the scientists know they had seen them.

“We analyzed brain oscillations that reflect fluctuations in excitability of a local brain region; in other words, how difficult or easy it is for a neuron to respond to an input,” Ms. Daitch said. “If areas of the brain involved in detecting a stimulus are at maximum excitability, you would be much more likely to notice the stimulus.”

Excitability typically increases and falls in the cells that comprise a specific brain region. But these oscillations normally are not aligned between different brain regions. The findings revealed that as patients directed their attention, the brain regions most important for paying attention to visual stimuli modified their excitability cycles, causing them to start hitting the peaks of their cycles at the same time. The excitability cycles did not vary in regions not involved in attention. “If the cycles of two brain regions are out of alignment, the chances that a signal from one region will get through to another region are reduced,” Dr. Corbetta said.

The scientists are now trying to determine whether knowing not just the location, but additionally the rhythm of the task, allows participants to bring the excitability of their brain regions into alignment more rapidly.

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Washington University School of Medicine in St. Louis