miércoles, 30 de junio de 2010

Is your left hand more motivated than your right hand?



Is your left hand more motivated than your right hand?
June 29th, 2010 in Medicine & Health / Psychology & Psychiatry

Motivation doesn't have to be conscious; your brain can decide how much it wants something without input from your conscious mind. Now a new study shows that both halves of your brain don't even have to agree. Motivation can happen in one side of the brain at a time.

Psychologists used to think that motivation was a conscious process. You know you want something, so you try to get it. But a few years ago, Mathias Pessiglione, of the Brain & Spine Institute in Paris, and his colleagues showed that motivation could be subconscious; when people saw subliminal pictures of a reward, even if they didn't know what they'd seen, they would try harder for a bigger reward.

In the earlier study, volunteers were shown pictures of either a one-euro coin or a one-cent coin for a tiny fraction of a second. Then they were told to squeeze a pressure-sensing handgrip; the harder they squeezed it, the more of the coin they would get. The image was subliminal, so volunteers didn't know how big a coin they were squeezing for, but they would still squeeze harder for one euro than one cent. That result showed that motivation didn't have to be conscious.

For the new study, in Psychological Science, a journal of the Association for Psychological Science, Pessiglione and his colleagues Liane Schmidt, Stefano Palminteri, and Gilles Lafargue wanted to know if they could dig even farther down and show that one side of the brain could be motivated at a time. The test started with having the subject focus on a cross in the middle of the computer screen. Then the motivational coin - one euro or one cent - was shown on one side of the visual field. People were only subliminally motivated when the coin appeared on the same side of the visual field as the squeezing hand. For example, if the coin was on the right and they were squeezing with the right hand, they would squeeze harder for a euro than for a cent. But if the subliminal coin appeared on the left and they were squeezing on the right, they wouldn't squeeze any harder for a euro.

The research shows that it's possible for only one side of the brain, and thus one side of the body, to be motivated at a time, says Pessiglione. "It changes the conception we have about motivation. It's a weird idea, that your left hand, for instance, could be more motivated than your right hand." He says this basic research helps scientists understand how the two sides of the brain get along to drive our behavior.

Provided by Association for Psychological Science

domingo, 27 de junio de 2010

The Effect of Visual Cues on Auditory Stream Segregation in Musicians and Non-Musicians

Jeremy Marozeau, Hamish Innes-Brown, David B. Grayden, Anthony N. Burkitt, Peter J. Blamey

Background

The ability to separate two interleaved melodies is an important factor in music appreciation. This ability is greatly reduced in people with hearing impairment, contributing to difficulties in music appreciation. The aim of this study was to assess whether visual cues, musical training or musical context could have an effect on this ability, and potentially improve music appreciation for the hearing impaired.
Methods

Musicians (N = 18) and non-musicians (N = 19) were asked to rate the difficulty of segregating a four-note repeating melody from interleaved random distracter notes. Visual cues were provided on half the blocks, and two musical contexts were tested, with the overlap between melody and distracter notes either gradually increasing or decreasing.
Conclusions

Visual cues, musical training, and musical context all affected the difficulty of extracting the melody from a background of interleaved random distracter notes. Visual cues were effective in reducing the difficulty of segregating the melody from distracter notes, even in individuals with no musical training. These results are consistent with theories that indicate an important role for central (top-down) processes in auditory streaming mechanisms, and suggest that visual cues may help the hearing-impaired enjoy music.

miércoles, 16 de junio de 2010

Experience shapes the brain's circuitry throughout adulthood


Experience shapes the brain's circuitry throughout adulthood
June 15th, 2010 in Medicine & Health / Neuroscience

The adult brain, long considered to be fixed in its wiring, is in fact remarkably dynamic. Neuroscientists once thought that the brain's wiring was fixed early in life, during a critical period beyond which changes were impossible. Recent discoveries have challenged that view, and now, research by scientists at Rockefeller University suggests that circuits in the adult brain are continually modified by experience.

The researchers, led by Charles D. Gilbert, Arthur and Janet Ross Professor and head of the Laboratory of Neurobiology, observed how neurons responsible for receiving input from a mouse's whiskers shift their relationships with one another after single whiskers are removed. The experiments explain how the circuitry of a region of the mouse brain called the somatosensory cortex, which processes input from the various systems in the body that respond to the sense of touch, can change. The findings will be published next week in the online, open access journal PLoS Biology.

The Gilbert lab has been studying changing neuronal connections for several years. Their approach, in which the scientists use a viral labeling system to attach fluorescent proteins to individual neurons and then image individual synapses in an intact, living brain with a high-resolution two-photon microscope, has provided several important clues to understanding the dynamics of the brain's wiring. Students in the Gilbert lab, Dan Stettler and Homare (Matias) Yamahachi, in collaboration with Winfried Denk at the Max Planck Institute in Heidelberg, previously followed the same neurons week after week in the primary visual cortex of adult monkeys. They found that the circuits of the visual cortex are highly dynamic, turning over synapses at a rate of seven percent per week. These changes occurred without any learning regimen or physical manipulations to the neurons.

Last year, Yamahachi, together with Sally Marik and Justin McManus, showed that when sensory experience is altered, even more dramatic changes in cortical circuits occur, with very rapid alterations in circuitry involving an exuberant growth of new connections paralleled by a pruning of old connections. These studies and others by the Gilbert lab have begun to show that there are underlying dynamics in the sensory cortex and it's not a fixed system, as has long been believed.

In the new study, Marik and other members of the Gilbert lab looked at excitatory and inhibitory neurons within the mouse cortex during periods of sensory deprivation to determine how experience shapes different components of cortical circuitry. For this study they used the whisker-barrel system in adult mice. The barrel cortex, part of the somatosensory cortex, receives sensory input from the animal's whiskers. Scientists have shown that after a row of whiskers is removed, barrels shift their representation to adjacent intact whiskers.

Marik, together with Yamahachi and McManus, found that after a whisker was plucked excitatory connections projecting into the deprived barrels underwent exuberant and rapid axonal sprouting. This axonal restructuring occurred rapidly — within minutes or hours after whiskers were plucked — and continued over the course of several weeks. At the same time that excitatory connections were invading the deprived columns, there was a reciprocal outgrowth of the axons of inhibitory neurons from the deprived to the non-deprived barrels. This suggests that the process of reshaping cortical circuits maintains the balance between excitation and inhibition that exists in the normal cortex.

"Previously we showed changes only in excitatory connections," Gilbert says. "We've now demonstrated a parallel involvement of inhibitory connections, and we think that inhibition may play a role equal in importance to excitation in inducing changes in cortical functional maps."

The new study also showed that changes in the inhibitory circuits preceded those seen in the excitatory connections, suggesting that the inhibitory changes may mediate the excitatory ones. This process, Gilbert says, mimics what happens in the brain during early postnatal development.

"It's surprising that the primary visual or somatosensory cortices are involved in plasticity and capable of establishing new memories, which previously had been considered to be a specialized function of higher brain centers," Gilbert says. "We are just beginning to tease apart the mechanisms of adult cortical plasticity. We hope to determine whether the circuit changes associated with recovery of function following lesions to the central and peripheral nervous systems also occur under normal conditions of perceptual learning."

More information: Marik SA, Yamahachi H, McManus JNJ, Szabo G, Gilbert CD (2010) Axonal Dynamics of Excitatory and Inhibitory Neurons in Somatosensory Cortex. PloS Biol 8(6): e1000395. doi:10.1371/journal.pbio.1000395


Provided by Public Library of Science

jueves, 10 de junio de 2010

Devenir Humain? The art of human enhancement.

'Sound' science offers platform for brain treatment and manipulation





'Sound' science offers platform for brain treatment and manipulation
June 9th, 2010 in Medicine & Health / Research


The ability to diagnose and treat brain dysfunction without surgery, may rely on a new method of noninvasive brain stimulation using pulsed ultrasound developed by a team of scientists led by William "Jamie" Tyler, a neuroscientist at Arizona State University. The approach, published in the journal Neuron on June 9, shows that pulsed ultrasound not only stimulates action potentials in intact motor cortex in mice but it also "elicits motor responses comparable to those only previously achieved with implanted electrodes and related techniques," says Yusuf Tufail, the lead author from ASU's School of Life Sciences.

Other techniques such as transcranial magnetic and deep brain stimulation, electroconvulsive shock therapy and transcranial direct current stimulation are used to treat a range of brain dysfunctions, including epilepsy, Parkinson's disease, chronic pain, coma, dystonia, psychoses and depression. However, most of these approaches suffer from "critical weaknesses," Tyler says, including requirements for surgery, low spatial resolution or genetic manipulations. Optogenetics, for example, is one state-of-the-art technology that merges genes from plants and other organisms with the intact brains of animals to offer control of neural circuitry.

"Scientists have known for more than 80 years that ultrasound can influence nerve activity," observes Tufail. "Pioneers in this field transmitted ultrasound into neural tissues prior to stimulation with traditional electrodes that required invasive procedures. Those studies demonstrated that ultrasound pre-treatments could make nerves more or less excitable in response to electrical stimulation.

"In our study, however, we used ultrasound alone to directly stimulate action potentials and drive intact brain activity without doing any kind of surgery," Tufail says.

"It is fascinating to witness these effects firsthand," he adds. Tufail is one of four doctoral students in ASU's School of Life Sciences who worked with Tyler on the project. The team also included Alexei Matyushov, an physics undergraduate student in ASU's Barrett Honors College working with Tyler, and Nathan Baldwin, a doctoral student in bioengineering, and Stephen Helms Tillery, an assistant professor, with ASU's Ira A. Fulton Schools of Engineering.

"We knew from some of our previous work that ultrasound could directly stimulate action potentials in dishes containing slices of brain tissue," says Tyler. "Moving to transmit ultrasound through the skin and skull to stimulate the intact brain inside a living animal posed a much greater challenge."

Despite such challenges, the study shows how ultrasound can be used to stimulate brain circuits with millimeter spatial resolution.
"We've come a long way from the observations of Scribonius Largus, a Roman physician in the 1st century A.D. who placed electric torpedo fish on headache sufferers' foreheads to ease their pain," Tyler quips. "Our method paves the way for using sound waves to study and manipulate brain function, as well as to diagnose and treat its dysfunction."

In addition to advancing hope for noninvasive treatments of brain injury and disease, the groups' experiments in deeper subcortical brain circuits also revealed that ultrasound may be useful for modifying cognitive abilities.

"We were surprised to find that ultrasound activated brain waves in the hippocampus known as sharp-wave ripples," Tufail says. "These brain activity patterns are known to underlie certain behavioral states and the formation of memories."

The scientists also found that ultrasound stimulated the production of brain-derived neurotrophic factor (BDNF) in the hippocampus - one of the most potent regulators of brain plasticity.

Tyler says the fact that ultrasound can be used to stimulate action potentials, meaningful brain wave activity patterns, and BDNF leads him to believe that, in the future, ultrasound will be useful for enhancing cognitive performance; perhaps even in the treatment of cognitive disabilities such as mental retardation or Alzheimer's disease.

Tyler's students have also collected data that suggests that repeated exposure to low intensity ultrasound does not pose a health risk to rodents. "We examined many aspects of brain health following stimulation and found that low-intensity ultrasound is safe for repeatedly stimulating the brains of mice," noted Anna Yoshihiro, a neuroscience doctoral student in ASU's College of Liberal Arts and Sciences and co-author of the journal article. Yoshihiro works to treat Parkinsonian monkeys and has achieved some early success in treating epileptic seizures in mice using ultrasonic neuromodulation.

Monica Li Tauchmann, Yoshihiro's contemporary and co-author on the article, recalls the first time the method worked: "I was helping with experiments. We were trying to stimulate the brain of a living mouse with ultrasound. Not a whole lot was happening at first. Then, Dr. Tyler changed some of the ultrasound waveform parameters and the mouse started moving. We spent the rest of that day repeating the stimulation and the mouse was perfectly fine. It recovered from anesthesia as if nothing had happened. I think we were all astonished."

Tyler believes that there are a host of potential applications for ultrasound in brain manipulation. Besides basic science and medical uses, ultrasound represents a core platform around which future brain-machine interfaces can also be designed for gaming, entertainment and communication purposes because of its noninvasive nature.

"Space travel, hand-held computers, the Internet, and global positioning - not even a lifetime ago these things were mere science fiction. Today, they are commonplace," Tyler says. "Maybe the next generation of social entertainment networks will involve downloading customized information or experiences from personalized computer clouds while encoding them into the brain using ultrasound. I see no reason to rule out that possibility."

"To be honest," he adds, "we simply don't know yet how far we can push the envelope. That is why many refer to the brain as the last frontier - we still have a lot to learn."

Provided by Arizona State University

jueves, 3 de junio de 2010

How does the human brain memorize a sound?

How does the human brain memorize a sound?
June 3rd, 2010 in Medicine & Health / Neuroscience


Sound repetition allows us to memorize complex sounds in a very quick, effective and durable way. This form of auditory learning, which was evidenced for the first time by French researchers from CNRS, ENS Paris, and Paris Descartes and Toulouse universities, is believed to occur in daily life to help us identify and memorize sound patterns; it allows, for example, immediate recognition of sounds which become familiar through experience, such as the voice of relatives.

The same mechanism is involved in the relearning of certain sounds, in particular when using hearing aids. This study, which has just been published in the journal Neuron, opens new perspectives for understanding the process of auditory memory.

“Until now, the only available data on acoustic memorization concerned simple sounds or language”, points out Daniel Pressnitzer. Three French researchers set themselves the challenge of addressing complex sounds and studying our ability to memorize them, as little was known on the subject.

In order to investigate how auditory memory is formed, the researchers subjected volunteers to various noise samples: these noises were generated in a totally random and unpredictable way to ensure that the volunteers would never have heard them before. Furthermore, these original complex sound waves had no meaning, and were perceived at first as an indistinct hiss. Listeners were not told that an identical complex noise pattern could be played several times during the experiment.

Using this fairly simple protocol, the scientists discovered that our ear is remarkably effective in detecting noise repetitions. Listeners nearly always recognized the noise pattern that had been played several times; two listenings were enough for those with a trained ear, and only about ten for less experienced ears. Sound repetition therefore induces both extremely rapid and effective learning, which occurs implicitly (it is not supervised). In addition, this memory for noise can last several weeks. A fortnight after the first experiment, volunteers identified the noise pattern again, at first attempt.

The scientists have demonstrated the existence of a form of fast, solid and long-lasting auditory learning. Their experimental protocol has proven to be a relevant and simple method that could make it possible to study auditory memory in both humans and animals. These results imply that a mechanism for rapid auditory plasticity - that is, a mechanism involved in an auditory neuron's ability to adapt its response to a given sound stimulant - plays a very effective role in the learning of sounds. This process is likely to be essential to identify and memorize recurrent sound patterns in our acoustic environment, such as the voice of relatives. It has all the characteristics considered necessary for human beings to learn to associate a sound with what produces it.

The same mechanism may also be involved in relearning, which is often inevitable when hearing suddenly changes. This is true of hearing-impaired people who start using hearing aids. A period of adaptation to their prosthesis is necessary so they can get used to hearing sounds they no longer heard or perceived differently. The researchers hope that one day they will be able to study the effect of the modifications introduced by hearing aids on re-learning more in depth.

More information: Sound illustrations: http://audition.ens.fr/memonoise/

Rapid formation of robust auditory memories: Insights from noise. Trevor R. Agus, Simon J. Thorpe, Daniel Pressnitzer. Neuron. May 27, 2010.

miércoles, 2 de junio de 2010

Cognitive ability, not age, predicts risky decisions



Just because your mother has turned 85, you shouldn't assume you'll have to take over her financial matters. She may be just as good or better than you at making quick, sound, money-making decisions, according to researchers at Duke University.

"It's not age, it's cognition that makes the difference in decision-making," said Scott Huettel, Ph.D., Associate Professor of psychology and neuroscience and director of the Duke Center for Neuroeconomic Studies. He recently led a laboratory study in which participants could gain or lose money based on their decisions.

"Once we accounted for cognitive abilities like memory and processing speed, age had nothing to do with predicting whether an individual would make the best economic decisions on the tasks we assigned," Huettel said.

The study was published in the Psychology and Aging journal, published by the American Psychological Association.

Duke researchers assigned a variety of economic tasks that required different types of risky decisions, so that participants could gain or lose real money. They also tested subjects' cognitive abilities - including both how fast they could process new information and how well they could remember that information. They worked with 54 older adults between 66 and 76 years of age and 58 younger adults between 18 and 35 years of age. .

The researchers used path analysis, a statistical method of finding cause-and-effect relationships, to determine whether age affected the economic decisions directly or whether it had indirect effects, such as age influencing memory, which in turn influenced decisions.

"The standard perspective is that age itself causes people to make more risky, lower-quality decisions - independent of the cognitive changes associated with age," said Huettel, who is also with the Duke-UNC Brain Imaging and Analysis Center. "But that isn't what we found."

The path analyses showed that age-related effects were apparently linked to individual differences in processing speed and memory. When those variables were included in the analysis, age was no longer a significant predictor of decision quality, Huettel said.

On a bell curve of performance, there was overlap between the younger and older groups. Many of the older subjects, aged 66 to 76, made similar decisions to many of the younger subjects (aged 18 to 35). "The stereotype of all older adults becoming more risk-averse is simply wrong," Huettel said.

"Some of the older subjects we studied were able to make better decisions than younger subjects who scored lower on tests of their cognitive abilities," Huettel said. "If I took 20 younger adults and 20 older adults, all of whom were above average on these measures, then on average, you could not tell them apart based on decisions. On the whole, it is true, more older people process slowly and has poorer memory. But there are also older people who do as well as younger people."

Huettel said that the findings suggest strategies to assist people, such as allowing more time for decisions, or presenting data in certain ways to assist people in making decisions.

"Decision scaffolding is the concept that you can give people structure for decision-making that helps them," Huettel said. "We should try to identify ways in which to present information to older adults that gives them scaffolding to make the best choices. If we can reduce the demand on memory or the need to process information very quickly that would be a great benefit to older adults and may push them toward making the same economically beneficial decisions as younger adults."

In reality, younger adults more often work to obtain credit cards with lower interest rates and lower interest rates on mortgages, for example. Huettel said that using surveys that track real-world behavior might help to identify who would benefit from getting information in one manner versus another.

"Some younger adults, too, may benefit from getting their information in a slow, methodical way, while others may not," Huettel said. "We may be able to predict that based on cognition." Self-recognition is important, too, so that if someone knows they process things well over time, they might ask for more time to make a decision rather than making an impulsive decision on the spot, he added.

Provided by Duke University Medical Center
June 1st, 2010 in Medicine & Health / Psychology & Psychiatry