sábado, 29 de enero de 2011
Field of Attention for Instantaneous Object Recognition
Jian-Gao Yao 1, Xin Gao 1, Hong-Mei Yan 1, Chao-Yi Li 1,2
1 Key Laboratory for Neuroinformatics, Ministry of Education of China, University of Electronic Sciences and Technology, Chengdu, China,
2 Center for Life Sciences, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai, China
Instantaneous object discrimination and categorization are fundamental cognitive capacities performed with the guidance of visual attention. Visual attention enables selection of a salient object within a limited area of the visual field; we referred to as “field of attention” (FA). Though there is some evidence concerning the spatial extent of object recognition, the following questions still remain unknown: (a) how large is the FA for rapid object categorization, (b) how accuracy of attention is distributed over the FA, and (c) how fast complex objects can be categorized when presented against backgrounds formed by natural scenes.
To answer these questions, we used a visual perceptual task in which subjects were asked to focus their attention on a point while being required to categorize briefly flashed (20 ms) photographs of natural scenes by indicating whether or not these contained an animal. By measuring the accuracy of categorization at different eccentricities from the fixation point, we were able to determine the spatial extent and the distribution of accuracy over the FA, as well as the speed of categorizing objects using stimulus onset asynchrony (SOA). Our results revealed that subjects are able to rapidly categorize complex natural images within about 0.1 s without eye movement, and showed that the FA for instantaneous image categorization covers a visual field extending 20°×24°, and accuracy was highest (>90%) at the center of FA and declined with increasing eccentricity.
In conclusion, human beings are able to categorize complex natural images at a glance over a large extent of the visual field without eye movement.
viernes, 28 de enero de 2011
Beyond the bullet: Surviving a shot to the head carries host of challenges
January 28th, 2011 in Medicine & Health / Other
The spectral images, reproduced in neurosurgery journals and textbooks, could be captioned "Beauty and the Beast." Captured by X-ray and CT scan, the human brain is pierced by a bullet, nail, pool cue or chunk of razor-sharp debris. The intruding object has ripped a jagged vortex of destruction through the brain's gelatinous lobes and forged an even wider path of quivering shock.
If the projectile came in hard and fast, shards of broken skull will be scattered through the delicate tissue. The bullet might have ricocheted off bone and tumbled wildly in the cavity, bursting blood vessels and carving uneven holes where, only moments before, healthy brain cells had hummed.
Such havoc, you would think, would put an abrupt end to the brain's rhythmic buzz of activity and extinguish the life defined by its complex inner workings.
But - as the awakening of Rep. Gabrielle Giffords has demonstrated these last weeks - the human brain can be resilient, capable of withstanding brutish damage and then masterminding its reconstruction.
"I have seen every foreign body in the world pass through the brain, and I never cease to be amazed that some seem to survive and do amazingly well," said Dr. Ian Armstrong, a Century City, Calif., neurosurgeon, shortly after Giffords was shot.
Make no mistake: Bullets usually kill when they enter the brain. The U.S. Centers for Disease Control and Prevention estimates that in 90 percent of brain injuries that stem from firearms, the patient dies. Of the lucky 1 in 10, virtually all are thought to live with persistent disabilities.
In the last 15 years, however, better treatments have greatly improved the odds of survival. "In Iraq, we were fooled many times," said Duke University neurosurgeon Gerald Grant, who was an Air Force physician at Joint Base Balad in that country. Patients whose scans showed that shrapnel had crossed between the brain's hemispheres or cut a wide swath of destruction - injuries long thought to be a swift sentence of death - would often live.
But the result, as Giffords may yet show, is almost always a person profoundly changed by the injury.
As many as half of those who have had penetrating brain injury will suffer epileptic seizures and will have a higher risk of them for the rest of their lives, experts say.
Because these injuries often leave a victim fully conscious during and immediately after, many will retain vivid memories of the horror and suffer flashbacks, nightmares, anxiety and withdrawal, the hallmarks of post-traumatic stress disorder.
Vietnam veterans with a penetrating brain injury have shown steeper cognitive decline than that of their uninjured peers - apparently an accelerated version of normal age-related decline.
Beyond those broad strokes, the exact consequences of a penetrating brain injury depend heavily on where and at what speed the foreign body penetrated the skull.
"There are some parts of the brain that have high real estate value," says Dr. Jam Ghajar, president of the Brain Trauma Foundation and clinical professor of neurological surgery at Weill Cornell Medical College in New York City. "If you go into the brainstem, or a millimeter to the right or left, you can have massive disruption and almost certain death. You go into the frontal lobe and you have a lot more room for error."
The brain is a marvel of redundancy, parallel networks and interlocking message centers that might, with time, rewire around obstacles. But many clusters have precise functions - governing word access or face recognition, or processing vision, hearing and smell. Damage to those can cause specific, maybe permanent, impairments.
Damage to deep brain structures such as the amygdala or the hypothalamus will likely disturb a victim's ability to fully form, retain and retrieve memories that are freighted with emotion. Such impairments can wreak havoc on relationships and day-to-day functioning.
Some damage is subtler still. When a penetrating object has stretched or torn some tissue, including the connective "white matter" that forms bridges among brain regions, problems of attention, memory and social processing make it tough to navigate the demands of work, high-level thinking or new social situations.
Damage to the frontal lobes - common in traumatic brain injury because they lie right behind the forehead - can disturb a person's ability to formulate plans, read or respond to social cues, and suppress the impulse to do or say things that might be socially inappropriate.
Such impairments - labored speech, flat emotion, an odd social manner, an inability to make and carry out a plan - often linger. Those symptoms plague many of the estimated 5.3 million Americans who live with the persistent consequences of brain trauma. Little wonder that brain injury is often called the silent epidemic.
After the threat of death has passed, the challenge of regaining lost abilities - and of adjusting to life without others - is where the power of human resilience and inventiveness really inspires awe and humility, say those who have studied such injuries or witnessed the fallout up close.
"It's been a heartbreaking and inspiring thing to see," said Daniel Gross, whose younger brother Matthew, 41, was shot through the head 14 years ago by a gunman on the observation deck of New York's Empire State Building. After a week in a coma, Matthew first struggled to piece sentences together. Fully articulate after years of rehabilitation, he wrestles now with more subtle conventions of tactful conversation - the result of the bullet's passage through the frontal lobes on both sides of his brain.
Jordan Grafman, an expert on the long-term effects of penetrating trauma, says the survivors he has studied are remarkable not only for having survived but also for their determination to adapt and grow beyond their losses.
"At least half of our guys are working in full-time jobs and have families," says Grafman, director of research on brain injury at the Kessler Foundation in West Orange, N.J. "While people are uniformly left with impairments that are significant, they often show a tremendous ability to recover and really live productive and meaningful lives."
A patient's long-term recovery is profoundly affected by the person he or she was before the injury, Grafman says: A person who was clever, socially adept and intellectually engaged before the injury is likely to recover more lost capability than a person who had less mental horsepower or fewer social resources - friends, school, work, hobbies.
Grafman's conclusion comes from a unique cache of data: a decades-long study that has tracked some 200 Vietnam veterans who survived penetrating brain injury. The military's practice of testing troops for mental fitness gave researchers a standard gauge of intelligence and ability on each person that predated his injury. That provided a basis for measuring changes in a survivor's cognitive function in the decades after.
Ingoing scores on the armed forces' qualifying test have been the best predictor of a brain injury survivor's recovery from impairment, Grafman says. Now the study has begun to assess the influence of caregivers' styles - whether they are demanding or lenient, pushy or reserved, socially linked or more withdrawn.
Ironically, for those best equipped to rebuild their lives - people who, pre-injury, were exceptionally bright and highly motivated - the injury can pack a cruel surprise. Many grasp the extent of their impairments and are impatient to regain lost abilities that may never come back or that return at an agonizing snail's pace. Such survivors, Grafman says, are more vulnerable to depression and anxiety, which can impede progress and make life a misery.
As the nation tracks the recovery of Giffords, some worry about how the weight of expectations - and the Arizona Democrat's own formidable intelligence and drive - will affect her ability to overcome or adapt to the impairments likely to come with her injury.
One of them is Jackie Nink Pflug, who survived a bullet to her head at point-blank range during the 1985 hijacking of an EgyptAir flight from Athens to Cairo.
During years of painstaking recovery, Pflug relearned how to find her words, read a book, count money and navigate the world with seizures, excruciating headaches, a narrow field of vision, unreliable memory and the loss of hearing in one ear.
Asked what she would tell Giffords, Pflug urges her, above all, to "be patient with yourself."
In the first several years, she says, she sometimes "didn't know where the brain injury ended and the depression began." But rather than slow down, she pushed harder. "I wanted to do better, and my brain wasn't always ready for it."
Now, she says, "I'm just really good to myself." Giffords should be too, she adds.
"Even the littlest things, have a party about it."
(c) 2011, Los Angeles Times.
Distributed by McClatchy-Tribune Information Services.
jueves, 27 de enero de 2011
Teen brains over-process rewards, suggesting root of risky behavior, mental ills
January 26th, 2011 in Medicine & Health / Neuroscience
Each row represents the activity in a neuron at key times during the task. At the time of reward, nearly one-third of adolescent neurons became excited (shown in red) though the level of inhibition (in blue) changed marginally. Adult neurons registered much higher inhibitory activity and less excitation. Credit: B. Moghaddam
University of Pittsburgh researchers have recorded neuron activity in adolescent rat brains that could reveal the biological root of the teenage propensity to consider rewards over consequences and explain why adolescents are more vulnerable to drug addiction, behavioral disorders, and other psychological ills.
The team reports in the Journal of Neuroscience that electrode recordings of adult and adolescent brain-cell activity during the performance of a reward-driven task show that adolescent brains react to rewards with far greater excitement than adult brains. This frenzy of stimulation occurred with varying intensity throughout the study along with a greater degree of disorganization in adolescent brains. The brains of adult rats, on the other hand, processed their prizes with a consistent balance of excitation and inhibition.
The extreme difference in brain activity provides a possible physiological explanation as to why teenagers are more prone than adults to rash behavior, addiction, and mental diseases, said lead researcher Bita Moghaddam, a professor of neuroscience in Pitt's School of Arts and Sciences. She and coauthor David Sturman, a Pitt neuroscience doctoral student, observed the disparate reactions to reward in individual neurons in the orbitofrontal cortex, a brain region that weighs payoff and punishment to plan and make decisions.
"The disorganized and excess excitatory activity we saw in this part of the brain means that reward and other stimuli are processed differently by adolescents," Moghaddam said. "This could intensify the effect of reward on decision making and answer several questions regarding adolescent behavior, from their greater susceptibility to substance abuse to their more extreme reactions to pleasurable and upsetting experiences."
In addition, malfunctions in the orbitofrontal cortex have been observed in cases of schizophrenia, mood disorders, and other psychological disturbances, Moghaddam said. The type of erratic activity in the cortex that she and Sturman observed could aggravate these conditions at a time when the maturing brain is vulnerable.
"The symptoms of these illnesses generally begin to appear during adolescence," Moghaddam said. "Adolescence is a period of behavioral and psychiatric vulnerabilities, so the disorganized brain activity and excess excitation could push a brain already predisposed to mental disorders too far, triggering the onset of symptoms."
Adult and adolescent neural activity was similar at first. When a reward was expected (sessions 3-6), adolescent brain activity spiked, followed by a slow decrease after the sugar pellet was received (food trough entry). Adults experienced a similar rapid increase in activity followed by a quick return to baseline. Credit: B. Moghaddam
The study is the first to record and compare individual neuron activity in adult and adolescent brains during the performance of a task. Moghaddam and Sturman presented adult and adolescent rats—which exhibit behavioral and biological similarities to adult and teenage humans—with three holes to poke their noses through; the rats each received a sugar pellet when they chose the center hole.
Brain activity in the adolescents was similar to that of the adults most of the time but striking differences arose when the younger rats retrieved rewards. As each of the adult rats collected a sugar pellet, the orbitofrontal cortex neurons showed the normal increase in both excitation and inhibition, with consistent levels of each impulse throughout the study.
Adolescents, on the other hand, exhibited surges of excitation that ranged from twice to four times the levels in adults. At the same time, the inhibitory impulses in the adolescents' brains barely changed from the low levels they experienced before receiving the sugar pellet.
Provided by University of Pittsburgh
lunes, 24 de enero de 2011
Out of mind in a matter of seconds: How fast neuronal networks delete sensory information
January 24th, 2011 in Physics / General Physics
An activity pattern is comparable to a communication protocol. It indicates which neuron is active at a given time. Credit: MPI for Dynamics and Selforganisatio. The dynamics behind signal transmission in the brain are extremely chaotic. This conclusion has been reached by scientists from the Max Planck Institute for Dynamics and Self-Organization at the University of Gottingen. In addition, the researchers calculated, for the first time, how quickly information stored in the activity patterns of the cerebral cortex neurons is discarded. At one bit per active neuron per second, the speed at which this information is forgotten is surprisingly high.
The brain codes information in the form of electrical pulses, known as spikes. Each of the brain’s approximately 100 billion interconnected neurons acts as both a receiver and transmitter: these bundle all incoming electrical pulses and, under certain circumstances, forward a pulse of their own to their neighbours. In this way, each piece of information processed by the brain generates its own activity pattern. This indicates which neuron sent an impulse to its neighbours: in other words, which neuron was active, and when. Therefore, the activity pattern is a kind of communication protocol that records the exchange of information between neurons.
How reliable is such a pattern? Do even minor changes in the neuronal communication produce a completely different pattern in the same way that a modification to a single contribution in a conversation could alter the message completely? Such behaviour is defined by scientists as chaotic. In this case, the dynamic processes in the brain could not be predicted for long. In addition, the information stored in the activity pattern would be gradually lost as a result of small errors. As opposed to this, so-called stable, that is non-chaotic, dynamics would be far less error-prone. The behaviour of individual neurons would then have little or no influence on the overall picture.
The new results obtained by the scientists in Göttingen have revealed that the processes in the cerebral cortex, the brain’s main switching centre, are extremely chaotic. The fact that the researchers used a realistic model of the neurons in their calculations for the first time was crucial. When a spike enters a neuron, an additional electric potential forms on its cell membrane. The neuron only becomes active when this potential exceeds a critical value. "This process is very important", says Fred Wolf, head of the Theoretical Neurophysics research group at the Max Planck Institute for Dynamics and Self-Organization. "This is the only way that the uncertainty as to when a neuron becomes active can be taken into account precisely in the calculations".
Older models described the neurons in a very simplified form and did not take into account exactly how and under what conditions a spike arises. "This gave rise to stable dynamics in some cases but non-stable dynamics in others", explains Michael Monteforte from the Max Planck Institute for Dynamics and Self-Organization, who is also a doctoral student at the Göttingen Graduate School for Neurosciences and Molecular Biosciences (GGNB). It was thus impossible to resolve the long-established disagreement as to whether the processes in the cerebral cortex are chaotic or not, using these models.
Thanks to their more differentiated approach, the Gottingen-based researchers were able to calculate, for the first time, how quickly an activity pattern is lost through tiny changes; in other words, how it is forgotten. Approximately one bit of information disappears per active neuron per second. "This extraordinarily high deletion rate came as a huge surprise to us", says Wolf. It appears that information is lost in the brain as quickly as it can be "delivered" from the senses.
This has fundamental consequences for our understanding of the neural code of the cerebral cortex. Due to the high deletion rate, information about sensory input signals can only be maintained for a few spikes. These new findings therefore indicate that the dynamics of the cerebral cortex are specifically tailored to the processing of brief snapshots of the outside world.
More information: Physical Review Letters, 105, 268104 (2010).
Provided by Max-Planck-Gesellschaft
jueves, 20 de enero de 2011
Musicians' brains keep time--With one another
By Jordan Lite | Mar 16, 2009 08:01 PM
Ever wonder how musicians manage to play in unison? Credit their brain waves: they synchronize before and while musicians play a composition, according to new research.
German scientists report in BMC Neuroscience that they measured the brain waves of eight pairs of guitarists using electroencephalography (EEG) while they played a modern jazz piece called "Fusion #1" (by Alexander Buck). The researchers found that the guitarists' brain waves were aligned most during three pivotal times: when they were syncing up with a metronome, when they began playing the piece and at points during the composition that demanded the most synchrony.
The synchrony was most prominent in the frontal and central parts of the brain that regulate motor function. "Whenever synchrony of behavior was high, synchrony of brain waves were also high," Ulman Lindenberger, a director the Max Planck Institute for Human Development in Berlin, tells ScientificAmerican.com. But, "we can't assign a causal role to that synchronizing."
While brain synchrony during a duet seems like a given, it's a mystery how it happens, says Lindenberger, a psychologist. "One could speculate that this may be related to mirror neurons, the capacity of primates and humans to imagine the action of the other person while performing actions yourself," he says. "The mirror neuron system could be active during synchronized guitar playing."
Lindenberger says that inter-brain synchrony may also help explain humans' ability to engage in a host of other activities and behaviors that involve couples or teams, such as dancing, boxing, tennis and mother–child bonding. "People have an extraordinary capacity to synchronize their actions," he says. "When two people concentrate on the same thing, gestures and head movements are highly coordinated and supported by brain synchronicity. We think what we are getting through music has wider implications and social bonding behaviors are part of those wider implications."
martes, 18 de enero de 2011
The more you know a place, the more likely your memory will play spatial tricks
January 17th, 2011 in Medicine & Health / Psychology & Psychiatry
Using Northwestern University students, a new study shows that as students better understand the relationship between buildings on a campus, for example, over time memory biases cause them to exaggerate the distance between the north and south ends of campus.
Many suburbanites remember a time when they were once city dwellers. For a time many returned to the city for dining, cultural and entertainment purposes. But over time the suburbs and "the city" seemed much farther apart thereby resulting in less frequent trips.
A new Northwestern University study is the first to show that something may be happening cognitively that leads people to gradually become more biased, and at the same time more accurate, when it comes to their spatial memory as they become more familiar with a particular area.
In other words, as people better understand the relationship between buildings on a campus, for example, over time memory biases cause them to exaggerate the distance between the north and south ends of campus. They become more and more biased and see the boundaries of campus as being much farther apart.
David Uttal, professor of psychology in the Weinberg College of Arts and Sciences, along with colleague Alinda Friedman at the University of Alberta, are lead authors of the study. They witnessed firsthand how this plays out among students on the Northwestern campus.
“I’ve had students tell me that they may be a few minutes late for class because they are coming all the way from south campus,” Uttal said. “And I’m thinking, ‘It’s only a six-minute walk.’
“Another time I overheard a student say, ‘This better be good, because I don’t go to north campus for nothing.’
“That really intrigued me because if you look at a map it’s not at all clear where these divisions are,” said Uttal. “There are north and south ends of campus but treating it like a really sharp division, like a foreign world, it’s not justified based solely on geography. I think there is something really interesting going on here cognitively.”
There have been other studies demonstrating the existence of spatial biases and how they affect spatial judgments, but Uttal said there were never studies about how such biases developed and how they were learned.
By studying Northwestern freshmen over three quarters and comparing them to seniors, Uttal said two significant findings emerged.
First, Uttal said, “We can get simultaneously more accurate and more biased at the same time, which seems counterintuitive, but it really shows how different kinds of information are stored and thought about differently in the mind.”
Secondly, Uttal and his colleagues were able to establish a time-course for when these biases develop, concluding that when people are new to an area, they are not inherently biased. They develop biases as they become more familiar with their surroundings.
However, it is still unclear how people acquire information that lead to such biases.
“Part of it has to be somewhat cultural – so as you become more part of a group, a ‘northsider’ or ‘southsider’ if you will, you hear more about these distinctions,” Uttal said. “It’s also kind of an interaction between what you learn from other people and what you learn on your own.”
Uttal said the study’s findings have implications for both the Northwestern University community and society at large.
“One of the goals of our campus is to bring people closer together and establish community,” he said. “However, it is possible that people's cognitive biases could actually make this hard. If people start to think of different areas on campus as being farther apart as they get more involved in Northwestern, then it might actually be harder to get people to think about ‘One Northwestern’ the longer they are here.”
In addition, the study’s findings may have desegregation implications.
“As other researchers have shown, in segregated areas, people may tend to believe that they are farther apart than they really are,” Uttal said. “And if we’re trying to bring people together, we have to address the cognitive biases that they create. You tend to see the area that you’re close to as closer and the areas that are socially and cognitively further from you as being geographically farther. “
“Learning Fine-grained and Category Information in Navigable Real-World Space” was published in the journal Memory & Cognition in December. The study’s co-authors, in addition to Uttal and Friedman, are Linda Liu Hand and Christopher Warren, Northwestern University.
Provided by Northwestern University
viernes, 14 de enero de 2011
Neuroscientists explain 'Proustian effect' of small details attached to big memories
January 13th, 2011 in Medicine & Health / Neuroscience
Neuroscientists at MIT's Picower Institute of Learning and Memory have uncovered why relatively minor details of an episode are sometimes inexplicably linked to long-term memories. The work is slated to appear in the Jan. 13 issue of Neuron.
"Our finding explains, at least partially, why seemingly irrelevant information like the color of the shirt of an important person is remembered as vividly as more significant information such as the person's impressive remark when you recall an episode of meeting this person," said co-author Susumu Tonegawa, Picower Professor of Biology and Neuroscience and director of the RIKEN-MIT Center for Neural Circuit Genetics.
The data also showed that irrelevant information that follows the relevant event rather than precedes it is more likely to be integrated into long-term memory.
Shaping a memory
One theory holds that memory traces or fragments are distributed throughout the brain as biophysical or biochemical changes called engrams. The exact mechanism underlying engrams is not well understood.
MIT neuroscientists Arvind Govindarajan, assistant director of the RIKEN/MIT Center for Neural Circuit Genetics; Picower Institute postdoctoral associate Inbal Israely; and technical associate Shu-Ying Huang; and Tonegawa looked at single neurons to explore how memories are created and stored in the brain.
Previous research has focused on the role of synapses葉he connections through which neurons communicate. An individual synapse is thought to be the minimum unit necessary to establish a memory engram.
Instead of looking at individual synapses, the MIT study explored neurons' branch-like networks of dendrites and the multiple synapses within them.
Boosting the signal
Neurons sprout dendrites that transmit incoming electrochemical stimulation to the trunk-like cell body. Synapses located at various points act as signal amplifiers for the dendrites, which play a critical role in integrating synaptic inputs and determining the extent to which the neuron acts on incoming signals.
In response to external stimuli, dendritic spines in the cerebral cortex undergo structural remodeling, getting larger in response to repeated activity within the brain. This remodeling is thought to underlie learning and memory.
The MIT researchers found that a memory of a seemingly irrelevant detail葉he kind of detail that would normally be relegated to a short-term memory--may accompany a long-term memory if two synapses on a single dendritic arbor are stimulated within an hour and a half of each other.
"A synapse that received a weak stimulation, the kind that would normally accompany a short-term memory, will express a correlate of a long-term memory if two synapses on a single dendritic branch were involved in a similar time frame," Govindarajan said.
This occurs because the weakly stimulated synapse can steal or hitchhike on a set of proteins synthesized at or near the strongly stimulated synapse. These proteins are necessary for the enlargement of a dendritic spine that allows the establishment of a long-term memory.
"Not all irrelevant information is recalled, because some of it did not stimulate the synapses of the dendritic branch that happens to contain the strongly stimulated synapse," Israely said.
More information: "The dendritic branch is the preferred integrative unit for protein synthesis-dependent LTP," by Arvind Govindarajan, Inbal Israely, Shu-Ying Huang and Susumu Tonegawa. Neuron, 13 January, 2011.
Provided by Massachusetts Institute of Technology
jueves, 13 de enero de 2011
Research shows emotional stress can change brain function
January 12th, 2011 in Medicine & Health / Neuroscience
Research conducted by Iaroslav Savtchouk, a graduate student, and S. June Liu, PhD, Associate Professor of Cell Biology and Anatomy at LSU Health Sciences Center New Orleans, has shown that a single exposure to acute stress affected information processing in the cerebellum – the area of the brain responsible for motor control and movement coordination and also involved in learning and memory formation. The work is published in the January 12, 2011 issue of The Journal of Neuroscience.
The researchers found that a five-minute exposure to the odor of a predator produced the insertion of receptors containing GluR2 at the connections (synapses) between nerve cells in the brain. GluR2 is a subunit of a receptor in the central nervous system that regulates the transfer of electrical impulses between nerve cells, or neurons. The presence of GluR2 changed electrical currents in the cerebellum in a way that increased activity and altered the output of the cerebellar circuit in the brains of mice.
Our ability to learn from experience and to adapt to our environment depends upon synaptic plasticity – the ability of a neuron or synapse to change its internal parameters in response to its history. A change in the GluR2 receptor subunit has been observed both during normal learning and memory as well as during many pathological processes, including drug addiction, stress, epilepsy, and ischemic stroke. However, the effect of this change on neuronal function is not fully understood.
"Our results lead to the testable prediction that emotional stress could affect motor coordination and other cerebellum-dependent cognitive functions," notes Dr. Liu. "These results are also applicable to communication in other brain regions and circuits. A long term goal is to alleviate the burden of neurological disorders such as motor dysfunctions, drug addiction, PTSD, and stroke."
Next steps include further research to improve our understanding of the role GluR2 insertion plays in normal learning and functioning of the brain, why some neurons contain GluR2-lacking receptors, but not others, and how that affects their role in brain function.
Provided by Louisiana State University
sábado, 8 de enero de 2011
Babies process language in a grown-up way
January 7th, 2011 in Medicine & Health / Neuroscience
This graphic shows estimated brain activity (indicated by bright colors) in four infants. Credit: UC San Diego School of Medicine
Babies, even those too young to talk, can understand many of the words that adults are saying – and their brains process them in a grown-up way.
Combining the cutting-edge technologies of MRI and MEG, scientists at the University of California, San Diego show that babies just over a year old process words they hear with the same brain structures as adults, and in the same amount of time. Moreover, the researchers found that babies were not merely processing the words as sounds, but were capable of grasping their meaning.
This study was jointly led by Eric Halgren, PhD, professor of radiology in the School of Medicine, Jeff Elman, PhD, professor of cognitive science in the Division of Social Sciences, and first author, Katherine E. Travis, of the Department of Neurosciences and the Multimodal Imaging Laboratory, all at UC San Diego. The work is published this week in the Oxford University Press journal Cerebral Cortex.
"Babies are using the same brain mechanisms as adults to access the meaning of words from what is thought to be a mental 'database' of meanings, a database which is continually being updated right into adulthood," said Travis.
Previously, many people thought infants might use an entirely different mechanism for learning words, and that learning began primitively and evolved into the process used by adults. Determining the areas of the brain responsible for learning language, however, has been hampered by a lack of evidence showing where language is processed in the developing brain.
While lesions in two areas called Broca's and Wernicke's (frontotemporal) areas have long been known to be associated with loss of language skills in adults, such lesions in early childhood have little impact on language development. To explain this discordance, some have proposed that the right hemisphere and inferior frontal regions are initially critical for language, and that classical language areas of adulthood become dominant only with increasing linguistic experience. Alternatively, other theories have suggested that the plasticity of an infant's brain allows other regions to take over language-learning tasks if left frontotemporal regions are damaged at an early age.
In addition to studying effects of brain deficits, language systems can be determined by identifying activation of different cortical areas in response to stimuli. In order to determine if infants use the same functional networks as adults to process word meaning, the researchers used MEG – an imaging process that measures tiny magnetic fields emitted by neurons in the brain – and MRI to noninvasively estimate brain activity in 12 to 18-month old infants.
In the first experiment, the infants listened to words accompanied by sounds with similar acoustic properties, but no meaning, in order to determine if they were capable of distinguishing between the two. In the second phase, the researchers tested whether the babies were capable of understanding the meaning of these words. For this experiment, babies saw pictures of familiar objects and then heard words that were either matched or mismatched to the name of the object: a picture of a ball followed by the spoken word ball, versus a picture of a ball followed by the spoken word dog.
Brain activity indicated that the infants were capable of detecting the mismatch between a word and a picture, as shown by the amplitude of brain activity. The "mismatched," or incongruous, words evoked a characteristic brain response located in the same left frontotemporal areas known to process word meaning in the adult brain. The tests were repeated in adults to confirm that the same incongruous picture/word combinations presented to babies would evoke larger responses in left frontotemporal areas.
"Our study shows that the neural machinery used by adults to understand words is already functional when words are first being learned," said Halgren, "This basic process seems to embody the process whereby words are understood, as well as the context for learning new words." The researchers say their results have implications for future studies, for example development of diagnostic tests based on brain imaging which could indicate whether a baby has healthy word understanding even before speaking, enabling early screening for language disabilities or autism.
Provided by University of California - San Diego
jueves, 6 de enero de 2011
Gesturing while talking helps change your thoughts
January 5th, 2011 in Medicine & Health / Psychology & Psychiatry
Sometimes it's almost impossible to talk without using your hands. These gestures seem to be important to how we think. They provide a visual clue to our thoughts and, a new theory suggests, may even change our thoughts by grounding them in action.
University of Chicago psychological scientists Sian Beilock and Susan Goldin-Meadow are bringing together two lines of research: Beilock's work on how action affects thought and Goldin-Meadow's work on gesture. After a chat at a conference instigated by Ed Diener, the founding editor of Perspectives on Psychological Science, they designed a study together to look at how gesture affects thought.
For the study, published in Psychological Science, a journal of the Association for Psychological Science, Beilock and Goldin-Meadow had volunteers solve a problem known as the Tower of Hanoi. It's a game in which you have to move stacked disks from one peg to another. After they finished, the volunteers were taken into another room and asked to explain how they did it. (This is virtually impossible to explain without using your hands.) Then the volunteers tried the task again. But there was a trick: For some people, the weight of the disks had secretly changed, such that the smallest disk, which used to be light enough to move with one hand, now needed two hands.
People who had used one hand in their gestures when talking about moving the small disk were in trouble when that disk got heavier. They took longer to complete the task than did people who used two hands in their gestures—and the more one-handed gestures they used, the longer they took. This shows that how you gesture affects how you think; Goldin-Meadow and Beilock suggest that the volunteers had cemented how to solve the puzzle in their heads by gesturing about it (and were thrown off by the invisible change in the game).
In another version of the experiment, published in Perspectives in Psychological Science, the volunteers were not asked to explain their solution; instead, they solved the puzzle a second time before the disk weights were changed. But moving the disks didn't affect performance in the way that gesturing about the disks did. The people who gestured did worse after the disk weights switched, but the people who moved the disks did not—they did just as well as before. "Gesture is a special case of action. You might think it would have less effect because it does not have a direct impact on the world," says Goldin-Meadow. But she and Beilock think it may actually be having a stronger effect, "because gesturing about an act requires you to represent that act." You aren't just reaching out and handling the thing you're talking about; you have to abstract from it, indicating it by a movement of your hands.
In the article published in Perspectives in Psychological Science, the two authors review the research on action, gesture, and thought. Gestures make thought concrete, bringing movement to the activity that's going on in your mind.
This could be useful in education; Goldin-Meadow and Beilock have been working on helping children to understand abstract concepts in mathematics, physics, and chemistry by using gesture. "When you're talking about angular momentum and torque, you're talking about concepts that have to do with action," Beilock says. "I'm really interested in whether getting kids to experience some of these actions or gesture about them might change the brain processes they use to understand these concepts." But even in math where the concepts have little to do with action, gesturing helps children learn—maybe because the gestures themselves are grounded in action.
Provided by Association for Psychological Science
miércoles, 5 de enero de 2011
In Brief: The cocktail party problem
January 4th, 2011 in Medicine & Health / Research
People can identify a repeating sound in a noisy room, but only when the noise includes mixtures of distinct distracting sounds, according to a study published this week in the Proceedings of the National Academy of Sciences.
Sound researchers have pondered this so-called "cocktail party problem," which underlies the ability to focus on a specific, unfamiliar sound.
To determine how the auditory system parses sound seemingly effortlessly, Josh H. McDermott and colleagues presented listeners with a synthesized audio recording that resembled everyday sounds, such as spoken words and animal vocalizations.
When the target sound was presented with one other sound, the listeners heard the mixture as a single sound and were unable to identify the target correctly.
However, when the target sound was presented repeatedly, mixed with a distinct distracting sound each time, the listeners developed an impression of the repeating target and identified it in the mixtures.
Further, the listeners' ability to recognize the target sound depended on the number of different mixtures in the audio recording, not the number of times the target was presented.
Hence, the authors suggest, the auditory system detects sounds based on patterns of time and frequency, such as might be produced by feet pounding on pavement or by branches swaying in the wind, and interprets the patterns as sound sources.
More information: "Recovering sound sources from embedded repetition," by Josh H. McDermott, David Wrobleski, and Andrew J. Oxenham, Proceedings of the National Academy of Sciences, January 2010.
Provided by Proceedings of the National Academy of Sciences
sábado, 1 de enero de 2011
Tempo Rubato: Animacy Speeds Up Time in the Brain
Mauro Carrozzo 1,2, Alessandro Moscatelli 2, Francesco Lacquaniti 2,3,4
1 Institute of Neuroscience, National Research Council, Rome, Italy,
2 Laboratory of Neuromotor Physiology, Santa Lucia Foundation, Rome, Italy,
3 Centre of Space BioMedicine, University of Rome Tor Vergata, Rome, Italy,
4 Department of Neuroscience, University of Rome Tor Vergata, Rome, Italy
How do we estimate time when watching an action? The idea that events are timed by a centralized clock has recently been called into question in favour of distributed, specialized mechanisms. Here we provide evidence for a critical specialization: animate and inanimate events are separately timed by humans.
In different experiments, observers were asked to intercept a moving target or to discriminate the duration of a stationary flash while viewing different scenes. Time estimates were systematically shorter in the sessions involving human characters moving in the scene than in those involving inanimate moving characters. Remarkably, the animate/inanimate context also affected randomly intermingled trials which always depicted the same still character.
The existence of distinct time bases for animate and inanimate events might be related to the partial segregation of the neural networks processing these two categories of objects, and could enhance our ability to predict critically timed actions.