Posts tagged parietal cortex
Articles and news from the latest research reports.
Finally mapped: The brain region that distinguishes bits from bounty
In comparing amounts of things — be it the grains of sand on a beach, or the size of a sea gull flock inhabiting it — humans use a part of the brain that is organized topographically, researchers have finally shown. In other words, the neurons that work to make this “numerosity” assessment are laid out in a shape that allows those most closely related to communicate and interact over the shortest possible distance.
This layout, referred to as a topographical map, is characteristic of all primary senses — sight, hearing, touch, smell and taste — and scientists have long assumed that numerosity, while not a primary sense (but perceived similarly to one), might be characterized by such a map, too.
But they have not been able to find it, which has caused some doubt in the field as to whether a map for numerosity exists.
Now, however, Utrecht University’s Benjamin Harvey, along with his colleagues, have sussed out signals that illustrate the hypothesized numerosity map is real.
Numerosity, it is important to note, is distinct from symbolic numbers. “We use symbolic numbers to represent numerosity and other aspects of magnitude, but the symbol itself is only a representation,” Harvey said. He went on to explain that numerosity selectivity in the brain is derived from visual processing of image features, where symbolic number selectivity is derived by recognizing the shapes of numerals, written words, and linguistic sounds that represent numbers. “This latter task relies on very different parts of the brain that specialize in written and spoken language.”
Understanding whether the brain’s processing of numerosity and symbolic numbers is related, as we might be tempted to think, is just one area that will be better informed by Harvey’s new map.
To uncover it, he and his colleagues asked eight adult study participants to look at patterns of dots that varied in number over time, all the while analysing the neural response properties in a numerosity-linked part of their brain using high-field fMRI (functional magnetic resonance imaging). Use of this advanced neuroimaging method allowed them to scan the subjects for far fewer hours per sitting than would have been required with a less powerful scanning technology.
With the fMRI data that resulted, Harvey and his team used population receptive field modelling, which aims to measure neural response as directly and quantitatively as possible. “This was the key to our success,” Harvey said. It allowed the researchers to model the human fMRI response properties they observed following results of recordings from macaque neurons, in which numerosity experiments had been conducted more extensively.
Their efforts revealed a topographical layout of numerosity in the human brain; the small quantities of dots the participants observed were encoded by neurons in one part of the brain, and the larger quantities, in another.
This finding demonstrates that topography can emerge not just for lower-level cognitive functions, like the primary senses, but for higher-level cognitive functions, too.
"We are very excited that association cortex can produce emergent topographic structures," Harvey said.
Because scientists know a great deal about topographical maps (and have the tools to probe them), the work of Harvey et al. may help scientists better analyse the neural computation underlying number processing.
"We believe this will lead to a much more complete understanding of humans’ unique numerical and mathematical skills," Harvey said.
Having heard from others in the field about the difficulty associated with the hunt for a topographical map of numerosity, Harvey and colleagues were surprised to obtain the results they did.
They also found the variations between their subjects interesting.
"Every individual brain is a complex and very different system," Harvey explained. "I was very surprised then that the map we report is in such a consistent location between our subjects, and that numerosity preferences always increased in the same direction along the cortex."
"On the other hand," he continued, "the extent of individual differences … is also striking." Harvey explained that understanding the consequences of these differences for their subjects’ perception or task performance will require further study.
(Source: eurekalert.org)
A look inside children’s minds
University of Iowa study shows how 3- and 4-year-olds retain what they see around them
When young children gaze intently at something or furrow their brows in concentration, you know their minds are busily at work. But you’re never entirely sure what they’re thinking.
Now you can get an inside look. Psychologists led by the University of Iowa for the first time have peered inside the brain with optical neuroimaging to quantify how much 3- and 4-year-old children are grasping when they survey what’s around them and to learn what areas of the brain are in play. The study looks at “visual working memory,” a core cognitive function in which we stitch together what we see at any given point in time to help focus attention. In a series of object-matching tests, the researchers found that 3-year-olds can hold a maximum of 1.3 objects in visual working memory, while 4-year-olds reach capacity at 1.8 objects. By comparison, adults max out at 3 to 4 objects, according to prior studies.
“This is literally the first look into a 3 and 4-year-old’s brain in action in this particular working memory task,” says John Spencer, psychology professor at the UI and corresponding author of the paper, which appears in the journal NeuroImage.
The research is important, because visual working memory performance has been linked to a variety of childhood disorders, including attention-deficit/hyperactivity disorder (ADHD), autism, developmental coordination disorder as well as affecting children born prematurely. The goal is to use the new brain imaging technique to detect these disorders before they manifest themselves in children’s behavior later on.
“At a young age, children may behave the same,” notes Spencer, who’s also affiliated with the Delta Center and whose department is part of the College of Liberal Arts and Sciences, “but if you can distinguish these problems in the brain, then it’s possible to intervene early and get children on a more standard trajectory.”
Plenty of research has gone into better understanding visual working memory in children and adults. Those prior studies divined neural networks in action using function magnetic resonance imaging (fMRI). That worked great for adults, but not so much with children, especially young ones, whose jerky movements threw the machine’s readings off kilter. So, Spencer and his team turned to functional near-infrared spectroscopy (fNIRS), which has been around since the 1960s but has never been used to look at working memory in children as young as three years of age.
“It’s not a scary environment,” says Spencer of the fNIRS. “No tube, no loud noises. You just have to wear a cap.”
Like fMRI, fNIRS records neural activity by measuring the difference in oxygenated blood concentrations anywhere in the brain. You’ve likely seen similar technology when a nurse puts your finger in a clip to check your circulation. In the brain, when a region is activated, neurons fire like mad, gobbling up oxygen provided in the blood. Those neurons need another shipment of oxygen-rich blood to arrive to keep going. The fNIRS measures the contrast between oxygen-rich and oxygen-deprived blood to gauge which area of the brain is going full tilt at a point in time.
The researchers outfitted the youngsters with colorful, comfortable ski hats in which fiber optic wires had been woven. The children played a computer game in which they were shown a card with one to three objects of different shapes for two seconds. After a pause of a second, the children were shown a card with either the same or different shapes. They responded whether they had seen a match.
The tests revealed novel insights. First, neural activity in the right frontal cortex was an important barometer of higher visual working memory capacity in both age groups. This could help clinicians evaluate children’s visual working memory at a younger age than before, and work with those whose capacity falls below the norm, the researchers say.
Secondly, 4-year olds showed a greater use than 3-year olds of the parietal cortex, located in both hemispheres below the crown of the head and which is believed to guide spatial attention.
"This suggests that improvements in performance are accompanied by increases in the neural response," adds Aaron Buss, a UI graduate student in psychology and the first author on the paper. "Further work will be needed to explain exactly how the neural response increases—either through changes in local tuning, or through changes in long range connectivity, or some combination."
Older adult clumsiness linked to brain changes
For many older adults, the aging process seems to go hand-in-hand with an annoying increase in clumsiness — difficulties dialing a phone, fumbling with keys in a lock or knocking over the occasional wine glass while reaching for a salt shaker.
While it’s easy to see these failings as a normal consequence of age-related breakdowns in agility, vision and other physical abilities, new research from Washington University in St. Louis suggests that some of these day-to-day reaching-and-grasping difficulties may be be caused by changes in the mental frame of reference that older adults use to visualize nearby objects.
“Reference frames help determine what in our environment we will pay attention to and they can affect how we interact with objects, such as controls for a car or dishes on a table,” said study co-author Richard Abrams, PhD, professor of psychology in Arts & Sciences.
“Our study shows that in addition to physical and perceptual changes, difficulties in interaction may also be caused by changes in how older adults mentally represent the objects near them.”
The study, published in the journal Psychological Science, is co-authored by two recent graduates of the psychology graduate program at Washington University. The lead author, Emily K. Bloesch, PhD, is now a postdoctoral teaching associate at Central Michigan University. The third co-author, Christopher C. Davoli, PhD, is a postdoctoral psychology researcher at the University of Notre Dame.
When tested on a series of simple tasks involving hand movements, young people in this study adopted an attentional reference frame centered on the hand, while older study participants adopted a reference frame centered on the body.
Young adults, the researchers explain, have been shown to use an “action-centered” reference frame that is sensitive to the movements they are making. So, when young people move their hands to pick up an object, they remain aware of and sensitive to potential obstacles along the movement path. Older adults, on the other hand, tend to devote more attention to objects that are closer to their bodies — whether they are on the action path or not.
“We showed in our paper that older adults do not use an “action centered” reference frame. Instead they use a “body centered” one,” Bloesch said. “As a result, they might be less able to effectively adjust their reaching movements to avoid obstacles — and that’s why they might knock over the wine glass after reaching for the salt shaker.”
These findings mesh well with other research that has documented age-related physical declines in several areas of the brain that are responsible for hand-eye coordination. Older adults exhibit volumetric declines in the parietal cortex and intraparietal sulcus, as well as white-matter loss in the parietal lobe and precuneus. These declines may make the use of an action-centered reference frame difficult or impossible.
“These three areas are highly involved in visually guided hand actions like reaching and grasping and in creating attentional reference frames that are used to guide such actions. These neurological changes in older adults suggest that their representations of the space around them may be compromised relative to those of young adults and that, consequently, young and older adults might encode and attend to near-body space in fundamentally different ways,” the study finds.
As the U.S. population ages, research on these issues is becoming increasingly important. An estimated 60-to-70 percent of the elderly population reports difficulty with activities of daily living, such as eating and bathing and many show deficiencies in performing goal-directed hand movements. Knowing more about these aging-related changes in spatial representation, the researchers suggest, may eventually inspire options for skills training and other therapies to help seniors compensate for the cognitive declines that influence hand-eye coordination
(Source: news.wustl.edu)
The Hidden Costs of Cognitive Enhancement
Gentle electrical zaps to the brain can accelerate learning and boost performance on a wide range of mental tasks, scientists have reported in recent years. But a new study suggests there may be a hidden price: Gains in one aspect of cognition may come with deficits in another.
Researchers who study transcranial electrical stimulation, which uses electrodes placed on the scalp, see it as a potentially promising way to enhance cognition in neurological patients, struggling students, and perhaps even ordinary people. Scientists have used it to speed up rehab in people whose speech or movement has been affected by a stroke, and DARPA has studied it as a way to accelerate learning in intelligence analysts or soldiers on the lookout for bad guys and bombs.
Until now, the papers coming out of this field have reported one good-news finding after another.
“This is the first paper to my knowledge to show a cost associated with the gains in cognitive function,” said neuropsychologist Rex Jung of the University of New Mexico, who was not associated with the study. “It’s a really nice demonstration.”
Cognitive neuroscientist Roi Cohen Kadosh of the University of Oxford, who led the study, has been investigating brain stimulation to boost mathematical abilities. He has applied for a patent on a brain stimulator he hopes could help math-challenged students get a better grip on the basics, or even help the mathematically inclined perform even better.
Cohen Kadosh and his colleague Teresa Iuculano investigated 19 volunteers as they learned a new numerical system by trial and error. The new system was based on arbitrary symbols: A cylinder represented the number five, for example, and a triangle represented the number nine. In several training sessions the volunteers viewed pairs of symbols on a computer screen and pressed a key to indicate which one represented a bigger quantity. At first they had to guess, but they eventually learned which symbols corresponded with which numbers.
All of the volunteers wore electrodes on their scalp during these training session. Some received mild electrical stimulation that targeted the posterior parietal cortex, an area implicated in previous studies of numerical cognition. Others received stimulation of the dorsolateral prefrontal cortex, an area involved in a wide range of functions, including learning and memory. A third group received sham stimulation that caused a slight tingling of the skin but no change in brain activity.
Those who had the parietal area involved in numerical cognition stimulated learned the new number system more quickly than those who got sham stimulation, the researchers report in the Journal of Neuroscience. But at the end of the weeklong study their reaction times were slower when they had to put their newfound knowledge to use to solve a new task that they hadn’t seen during the training sessions. ”They had trouble accessing what they’d learned,” Cohen Kadosh said.
The volunteers who had the prefrontal area involved in learning and memory stimulated showed the opposite pattern. They were slower than the control group to learn the new numerical system, but they performed faster on the new test at the end of the experiment. The bottom line, says Cohen Kadosh, is that stimulating either brain region had both benefits and drawbacks. ”Just like with drugs, there seem to be side effects,” he said.
Going forward, Cohen Kadosh says, more work is needed on how to maximize the benefits and minimize the costs of electrical brain stimulation. He thinks the approach has promise, but only when it’s used strategically, by picking the right brain regions to target and stimulating them while a person is training on the skill they want to improve. ”I think it’s going to be useless unless you pair it with some type of cognitive training,” he said.
But that’s not stopping some people from giving it a try on their own. Although it should be obvious that DIY brain stimulation is a bad idea, both Jung and Cohen Kadosh say there seems to be growing interest in the general public in using it for cognitive enhancement.
“There are some do it yourself websites I’ve stumbled across that are pretty frightening,” Jung said. “People are definitely tinkering around with this in their garage.”
The new study suggests one way that could backfire. And that’s not all, said Jung. ”You can burn yourself if nothing else.”
A region of the brain known to play a key role in visual and spatial processing has a parallel function: sorting visual information into categories, according to a new study by researchers at the University of Chicago.
Primates are known to have a remarkable ability to place visual stimuli into familiar and meaningful categories, such as fruit or vegetables. They can also direct their spatial attention to different locations in a scene and make spatially-targeted movements, such as reaching.
The study, published in the March issue of Neuron, shows that these very different types of information can be simultaneously encoded within the posterior parietal cortex. The research brings scientists a step closer to understanding how the brain interprets visual stimuli and solves complex tasks.
“We found that multiple functions can be mapped onto a particular region of the brain and even onto individual brain cells in that region,” said study author David Freedman, PhD, assistant professor of neurobiology at the University of Chicago. “These functions overlap. This particular brain area, even its individual neurons, can independently encode both spatial and cognitive signals.”
Freedman studies the effects of learning on the brain and how information is stored in short-term memory, with a focus on the areas that process visual stimuli. To examine this phenomenon, he has taught monkeys to play a simple video game in which they learn to assign moving visual patterns into categories.
“The task is a bit like a baseball umpire calling balls and strikes,” he said, “since the monkeys have to sort the various motion patterns into two groups, or categories.”
The monkeys master the tasks over a few weeks of training. Once they do, the researchers record electrical signals from parietal lobe neurons while the subjects perform the categorization task. By measuring electrical activity patterns of these neurons, the researchers can decode the information conveyed by the neurons’ activity.
“The activity patterns in these parietal neurons carry strong information about the category that each motion pattern gets assigned to during the task,” Freedman said.
(Image: Thinkstock)
Out of Sight, Out of Mind? How the brain codes its surroundings beyond the field of view
Even when they are not directly in sight, we are aware of our surroundings: so it is that when our eyes are fixed on an interesting book, for example, we know that the door is to the right, the bookshelf is to the left and the window is behind us. However, research into the brain has so far concerned itself predominantly with how information from our field of vision is coded in the visual cortex. To date it has not been known how the brain codes our surroundings beyond the field of view from an egocentric perspective (that is, from the point of view of the observer).
In the latest issue of the renowned journal Current Biology, Andreas Schindler und Andreas Bartels, scientists at the Werner Reichardt Center for Integrative Neuroscience (CIN) of the University of Tübingen, present for the first time direct evidence of this kind of spatial information in the brain.
The participants in their study found themselves in the center of a virtual octagonal room, with a unique object in each corner. As the brain’s activity was monitored by means of functional magnetic resonance imaging, the participants stood in front of one corner and looked at its object. Now they were instructed to determine the position of a second randomly chosen object within the room relative to their current perspective (for example, the object behind them). After a few trials the participant turned around so that the next object was brought into the field of view and the task was set up again. The whole procedure was repeated until every object had been looked at once.
The scientists discovered that patterns of activity in the parietal cortex code the participant’s egocentric position, that is, the relative position to his or her surroundings. The spatial information discovered there proved to be independent of the particular object, its absolute position in the room or that of the observer – i.e. it encoded egocentric spatial information of the three-dimensional surroundings. This result turns out to be particularly interesting because damage to the brain in the parietal cortex can lead to serious disruption of egocentric spatial awareness. Hence it is difficult for patients suffering from optical ataxia to carry out coordinated grasping movements. Lesions in the parietal cortex can also lead to a symptom called spatial neglect where patients have difficulties in perceiving their surroundings on the side opposite to the lesion. The brain areas identified in the present study coincided precisely with the areas of brain damage in such patients and provide for the first time insights regarding their function in the healthy brain.