How the brain pays attention to faces and places
Researchers identified areas of the brain that help us target our attention to objects, such as faces. The finding offers insight into how our brains are able to focus attention on key tasks amid a barrage of distracting sensory information.
Have you ever tried to find a friend in a large crowd? If you know where your friend is located, you can focus your attention on spatial details to search for her. This type of selective focus is known as spatial attention. Another option is to search for your friend's face. To do this, your brain has to recall the memory of her face and then try to match it without getting distracted by all the other sights and sounds of the crowd. This is known as object-based attention.
The prefrontal cortex area of the brain oversees important functions such as judgment, decision making, and problem solving, as well as emotional control and memory. While the brain areas working with the cortex to focus spatial attention have been identified, the regions involved in object-based attention have been less clear. Drs. Daniel Baldauf and Robert Desimone of the McGovern Institute at MIT set out to gain a better understanding. Their work was funded in part by NIH's National Eye Institute (NEI). Results appeared on April 25, 2014, in Science.
The researchers asked 12 participants to view a stream of images that included faces and houses. The images appeared sequentially in the exact same location so the brain couldn't use spatial information to distinguish them. Using magnetoencephalography (MEG), the scientists measured the participants' brain function while they focused on either houses or faces.
The face and house images were shown in different time patterns-2 images per second or 1.5 images per second. Since MEG can distinguish brain activity on a millisecond scale, the researchers were able to match areas of brain activity with different time patterns. By aligning the time-based MEG results with higher resolution fMRI data, they were able to pinpoint specific brain areas involved in object-based attention.
When participants paid attention to faces, activity increased in the fusiform face area (FFA) of the brain. When participants focused on houses, activity was enhanced in the parahippocampal place area (PPA). Increased activity in these areas occurred in concert with activity in the inferior frontal junction, an area of the prefrontal cortex that controls visual processing areas.
The neural activity in the inferior frontal junction typically appeared 20 milliseconds before activity in the FFA or PPA. This is the amount of time it takes for neurons to transmit information from the inferior frontal junction to the FFA or PPA. The finding suggests that the inferior frontal junction may direct the flow of visual processing during object-based attention.
"The interactions are surprisingly similar to those seen in spatial attention. It seems like it's a parallel process involving different areas," Desimone says.
Desimone and his team are interested in how the human brain deals with the information overload around us. The ability of brain regions to activate neurons in harmony with each other, thereby elevating a specific signal above the background noise, is extremely important, and may be impaired in many brain disorders.
-by Carol Torgan, Ph.D.
--From the National Institute of Health
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