Source of Key Brain Function Located: How to Comprehend a Scene in Less Than a Second

Source of Key Brain Function Located: How to Comprehend a Scene in Less Than a Second

  9:44:00 PM    Science Lover

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Scientists at the University of Southern California have pinned down the region of the brain responsible for a key survival trait: our ability to comprehend a scene -- even one never previously encountered -- in a fraction of a second.

The intraparietal sulcus (IPS), a groove in the brain 
closer to the top of the head, is engaged with 
implementing visual attention. Above: Lateral surface 
of left cerebral hemisphere, viewed from the side. 
Intraparietal sulcus visible at upper right, running 
horizontally. (Credit: Gray / Wikimedia Commons, 
public domain)

The key is to process the interacting objects that comprise a scene more quickly than unrelated objects, according to corresponding author Irving Biederman, professor of psychology and computer science in the USC Dornsife College and the Harold W. Dornsife Chair in Neuroscience.

The study appears in the June 1 issue of The Journal of Neuroscience.

The brain's ability to understand a whole scene on the fly "gives us an enormous edge on an organism that would have to look at objects one by one and slowly add them up," Biederman said. What's more, the interaction of objects in a scene actually allows the brain to identify those objects faster than if they were not interacting.

While previous research had already established the existence of this "scene-facilitation effect," the location of the part of the brain responsible for the effect remained a mystery. That's what Biederman and lead author Jiye G. Kim, a graduate doctoral student in Biederman's lab, set out to uncover with Chi-Hung Juan of the Institute of Cognitive Neuroscience at the National Central University in Taiwan.

"The 'where' in the brain gives us clues as to the 'how,'" Biederman said. This study is the latest in an ongoing effort by Biederman and Kim to unlock the complex way in which the brain processes visual experience. The goal, as Biederman puts it, is to understand "how we get mind from brain."

To find out the "where" of the scene-facilitation effect, the researchers flashed drawings of pairs of objects for just 1/20 of a second. Some of these objects were depicted as interacting, such as a hand grasping for a pen, and some were not, with the hand reaching away from the pen. The test subjects were asked to press a button if a label on the screen matched either one of the two objects, which it did on half of the presentations.

A recent study by Kim and Biederman suggested that the source of the scene-facilitation effect was the lateral occipital cortex, or LO, which is a portion of the brain's visual processing center located between the ear and the back of the skull. However, the possibility existed that the LO was receiving help from the intraparietal sulcus, or IPS, which is a groove in the brain closer to the top of the head.

The IPS is engaged with implementing visual attention, and the fact that interacting objects may attract more attention left open the possibility that perhaps it was providing the LO with assistance.

While participants took the test, electromagnetic currents were used to alternately zap subjects' LO or IPS, temporarily numbing each region in turn and preventing it from providing assistance with the task.

All of the participants were pre-screened to ensure they could safely receive the treatment, known as transcranial magnetic stimulation (TMS), which produces minimal discomfort.

By measuring how accurate participants were in detecting objects shown as interacting or not interacting when either the LO or IPS were zapped, researchers could see how much help that part of the brain was providing. The results were clear: zapping the LO eliminated the scene-facilitation effect. Zapping the IPS, however, did nothing.

When it comes to providing a competitive edge in identifying objects that are part of an interaction, the lateral occipital cortex appears to be working alone. Or, at least, without help from the intraparietal sulcus.

The research was funded through Biederman's National Science Foundation grants as well as a competitive grant awarded to Kim by the National Science Foundation designed to allow US students to collaborate with scientists in East Asia. Kim worked with Chi-Hung Juan, an expert in transcranial magnetic stimulation.

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Right or Left? Brain Stimulation Can Change Which Hand You Favor

Right or Left? Brain Stimulation Can Change Which Hand You Favor

  10:11:00 AM    Science Lover

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Each time we perform a simple task, like pushing an elevator button or reaching for a cup of coffee, the brain races to decide whether the left or right hand will do the job. But the left hand is more likely to win if a certain region of the brain receives magnetic stimulation, according to new research from the University of California, Berkeley.

When the left posterior parietal cortex of the brain received magnetic stimulation, right-handed volunteers were more likely to use their left hand to perform simple one-handed tasks, UC Berkeley research shows. (Credit: Image courtesy of Flavio Oliveira)

UC Berkeley researchers applied transcranial magnetic stimulation (TMS) to the posterior parietal cortex region of the brain in 33 right-handed volunteers and found that stimulating the left side spurred an increase in their use of the left hand.

The left hemisphere of the brain controls the motor skills of the right side of the body and vice versa. By stimulating the parietal cortex, which plays a key role in processing spatial relationships and planning movement, the neurons that govern motor skills were disrupted.

"You're handicapping the right hand in this competition, and giving the left hand a better chance of winning," said Flavio Oliveira, a UC Berkeley postdoctoral researcher in psychology and neuroscience and lead author of the study, published in the journal Proceedings of the National Academy of Sciences.

The study's findings challenge previous assumptions about how we make decisions, revealing a competitive process, at least in the case of manual tasks. Moreover, it shows that TMS can manipulate the brain to change plans for which hand to use, paving the way for clinical advances in the rehabilitation of victims of stroke and other brain injuries.

"By understanding this process, we hope to be able to develop methods to overcome learned limb disuse," said Richard Ivry, UC Berkeley professor of psychology and neuroscience and co-author of the study.

At least 80 percent of the people in the world are right-handed, but most people are ambidextrous when it comes to performing one-handed tasks that do not require fine motor skills.

"Alien hand syndrome," a neurological disorder in which victims report the involuntary use of their hands, inspired researchers to investigate whether the brain initiates several action plans, setting in motion a competitive process before arriving at a decision.

While the study does not offer an explanation for why there is a competition involved in this type of decision making, researchers say it makes sense that we adjust which hand we use based on changing situations. "In the middle of the decision process, things can change, so we need to change track," Oliveira said.

In TMS, magnetic pulses alter electrical activity in the brain, disrupting the neurons in the underlying brain tissue. While the current findings are limited to hand choice, TMS could, in theory, influence other decisions, such as whether to choose an apple or an orange, or even which movie to see, Ivry said.

With sensors on their fingertips, the study's participants were instructed to reach for various targets on a virtual tabletop while a 3-D motion-tracking system followed the movements of their hands. When the left posterior parietal cortex was stimulated, and the target was located in a spot where they could use either hand, there was a significant increase of the use of the left hand, Oliveira said.

Other coauthors of the study are Jörn Diedrichsen from University College London, Timothy Verstynen from the University of Pittsburg and Julie Duque from the Université Catholique de Louvain in Belgium.

The study was funded by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institutes of Health Research, the National Institutes of Health, the National Science Foundation and the Belgian American Educational Foundation.

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