Neuroscience
Month
12 August 2012
Certain brain regions in people with major depression are smaller and less dense than those of their healthy counterparts. Now, researchers have traced the genetic reasons for this shrinkage.
A series of genes linked to the function of synapses, or the gaps between brain cells crucial for cell-to-cell communication, can be controlled by a single genetic “switch” that appears to be overproduced in the brains of people with depression, a new study finds.
"We show that circuits normally involved in emotion, as well as cognition, are disrupted when this single transcription factor is activated," study researcher Ronald Duman, a professor of psychiatry at Yale University, said in a statement.
Shrinking brain
Brain-imaging studies, post-mortem examinations of human brains and animal studies have all found that in depression, a part of the brain called the dorsolateral prefrontal cortex shrinks. The neurons in this region, which is responsible for complex tasks from memory and sensory integration to the planning of actions, are also smaller and less dense in depressed people compared with healthy people.
Duman and his colleagues suspected that these neuronal abnormalities would include problems with the synapses, the points where brain cells “talk” to one another. At synapses, neurons release neurotransmitters that are picked up by their neighbors, carrying signals from cell to cell at rapid speed.
The researchers conducted gene profiling on the postmortem brain tissue of both depressed and mentally healthy subjects. They found a range of genes that were significantly less active in depressed people’s dorsolateral prefrontal cortexes, particularly five related to synaptic function: synapsin 1, Rab3A, calmodulin 2, Rab4B and TUBB4.
Synaptic damage
These genes are all involved in either the chemical signaling that occurs at synapses or the cellular recycling and regeneration processes that keep the synapse-system humming. All five are regulated by a single transcription factor called GATA1, which was overproduced in depressed brains.
The researchers activated GATA1 in the brains of rats and found that the factor decreased the complexity of the long, branchlike projections, or dendrites, of brain cells. These projections are the telephone lines that carry synaptic messages, integrating all the information a cell receives.
Extra GATA1 also increased depression-like behavior in the rats. For example, when given a swimming task, rats with extra GATA1 stayed immobile in the water longer, a signal of despair, than normal-GATA1 rats, the researchers report today (Aug. 12) in the journal Nature Medicine.
The researchers believe the damage could be a result of chronic stress, and they hope the findings lead to new depression treatments.
"We hope that by enhancing synaptic connections, either with novel medications or behavioral therapy, we can develop more effective antidepressant therapies," Duman said.
Source: Live Science
August 10, 2012
Most people have been in a situation that suddenly feels strangely familiar, while also realizing that they have never been in that specific place before. These experiences are called ‘déjà vu’ and the phenomenon has inspired countless books, songs and movies.
What is remarkable about déjà vu, says Western University graduate student Chris Martin, is that the impression of familiarity is accompanied by a sense that the current environment or situation should in fact feel new. But how can it be that a scene or an experience evokes a sense of familiarity but at the same time a feeling that this familiarity is wrong?
Despite the curiosity and excitement about déjà vu in popular culture, these subjective experiences remain poorly understood in scientific terms. Studying déjà vu has proven difficult due to the fleeting nature of these obscure occurrences, and due to the lack of experimental procedures to elicit them in the psychological laboratory.
In an article published online by Neuropsychologia, “Déjà Vu in Unilateral Temporal-Lobe Epilepsy is Associated with Selective Familiarity Impairments on Experimental Tasks of Recognition Memory,” Martin and psychology professor Stefan Köhler were able to shed light on this fascinating phenomenon by examining a rare group of neurological patients that experience déjà vu as an early sign of advancing seizures.
Due to lasting underlying brain pathology, most patients with temporal lobe epilepsy exhibit subtle impairments in memory even at times when no seizures are present. Köhler and his team built on this link by seeking behavioural markers of déjà vu on specific memory tasks that were designed to probe feelings of familiarity. The researchers discovered a pattern of performance that clearly distinguished patients with déjà vu from those without.
Specifically, familiarity was selectively impaired only in individuals with déjà vu in their seizure profile. In an experiment that placed different types of memories in conflict, patients with déjà vu were still able to counteract inappropriate feelings of familiarity with their ability to recollect pertinent information about previous actual events.
These findings, say Köhler and Martin, open a new window towards understanding the psychological and neural mechanisms that give rise to fleeting, subjective feelings of déjà vu. Köhler says they remind us that even when lasting for just a split second, memory experiences reflect the interplay of many different, sometimes competing processes. On another level, these findings are also of clinical relevance in the surgical treatment of temporal lobe epilepsy.
Source: University of Western Ontario
August 11th, 2012
By Laura Sanders
Lifting neural constraints could turn back time, making way for youthful flexibility
Michael Morgenstern
A baby’s brain is a thirsty sponge, slurping up words, figuring out faces and learning which foods are good and bad to eat. Information about the world flooding into a young brain begins to carve out traces, like rushing water over soft limestone. As the outside world sculpts the growing brain, important connections between nerve cells become strong rivers, while smaller unused tributaries quietly disappear.
In time, these brain connections crystallize, forming indelible patterns etched into marble. Impressionable brain systems that allowed a child to easily learn a language, for instance, go away, abandoned for the speed and strength that come with rigidity. In a fully set brain, signals fly around effortlessly, making commonplace tasks short work. A master of efficiency, the adult brain loses the exuberance of childhood.
But the adult brain need not remain in this petrified state. In a feat of neural alchemy, the brain can morph from marble back to limestone.
The potential for this metamorphosis has galvanized scientists, who now talk about a mind with the power to remake itself. In the last few years, researchers have found ways to soften the stone, recapturing some of the lost magic of a young brain.
“There’s been a very, very significant change,” says Richard Davidson of the University of Wisconsin–Madison. “I don’t think the import of that basic fact has fully expressed itself.”
Though this research is still in its early stages, studies suggest techniques that dissolve structures that pin brain cells in place, interrupt molecular stop signals and tweak the rush of nerve cell activity can restore the brain’s youthful glow. Scientists are already attempting to reverse brain rigidity, boosting what’s known as “plasticity” in people with a vision disorder once thought to be irreversible in adults.
These efforts are not an exercise in neural vanity. A malleable brain, researchers hope, can heal after a stroke, combat the decline in vision that comes with old age and perhaps even repair a severed spinal cord. An end to childhood — and the prodigal learning that comes with it — does not need to eliminate the brain’s capacity for change. “There are still windows of opportunity out there,” says neuroscientist Daphné Bavelier of the University of Rochester in New York. “It may require a little more work to open them, though.”
10 August 2012 by Helen Thomson
A woman born missing a finger and a thumb has grown them back – albeit as part of a phantom limb. This extraordinary occurrence shows that our brain contains a fully functional map of our body image, regardless of what our limbs actually look like.
The woman, RN, was born with just three fingers on her right hand. Aged 18, RN had the hand amputated after a car accident. She later began to feel that her missing limb was still present, and developed a “phantom” hand.
"But here’s the interesting thing," says Paul McGeoch at the University of California, San Diego. "Her phantom hand didn’t have three digits, it had five."
RN was aware of a full complement of fingers, but her phantom thumb and index finger were less than half the usual length.
With training using a mirror box trick – a tool that creates the visual illusion of two hands – McGeoch and V.S Ramachandran, also at San Diego, managed to extend her short phantom finger and thumb to normal length.
McGeoch says this study indicates that there is a hardwired representation in the brain of what the body should look like, regardless of how it actually appears in real life. It shows us more about the balance between the external and innate representations of a limb, he says.
"The presence of the deformed hand was suppressing the brain’s innate representation of her fingers which is why they appeared shorter, but after the hand was removed and the inhibition taken away, the innate representation kicks in again."
Matthew Longo at Birkbeck, University of London, says it is a fascinating case study. “It contributes to a growing literature suggesting that our conscious experience of our body is, at least in part, dependent on the intrinsic organisation of the brain, rather than a result of experience.”
Source: NewScientist
August 10, 2012
Scientists affiliated with the UC Davis MIND Institute have discovered how a defective gene causes brain changes that lead to the atypical social behavior characteristic of autism. The research offers a potential target for drugs to treat the condition.
Earlier research already has shown that the gene is defective in children with autism, but its effect on neurons in the brain was not known. The new studies in mice show that abnormal action of just this one gene disrupted energy use in neurons. The harmful changes were coupled with antisocial and prolonged repetitive behavior — traits found in autism.
The research is published online today in the scientific journal PLoS ONE.
"A number of genes and environmental factors have been shown to be involved in autism, but this study points to a mechanism — how one gene defect may trigger this type of neurological behavior," said study senior author Cecilia Giulivi, professor of molecular biosciences in the UC Davis School of Veterinary Medicine and a researcher affiliated with the UC Davis MIND Institute.
"Once you understand the mechanism, that opens the way for developing drugs to treat the condition," she said.
The defective gene appears to disrupt neurons’ use of energy, Giulivi said, the critical process that relies on the cell’s molecular energy factories called mitochondria.
In the research, a gene called pten was tweaked in the mice so that neurons lacked the normal amount of pten’s protein. The scientists detected malfunctioning mitochondria in the mice as early as 4 to 6 weeks after birth.
By 20 to 29 weeks, DNA damage in the mitochondria and disruption of their function had increased dramatically. At this time the mice began to avoid contact with their litter mates and engage in repetitive grooming behavior. Mice without the single gene change exhibited neither the mitochondria malfunctions nor the behavioral problems.
The antisocial behavior was most pronounced in the mice at an age comparable in humans to the early teenage years, when schizophrenia and other behavioral disorders become most apparent, Giulivi said.
The research showed that, when defective, pten’s protein interacts with the protein of a second gene known as p53 to dampen energy production in neurons. This severe stress leads to a spike in harmful mitochondrial DNA changes and abnormal levels of energy production in the cerebellum and hippocampus — brain regions critical for social behavior and cognition.
Pten mutations previously have been linked to Alzheimer’s disease as well as a spectrum of autism disorders. The new research shows that when pten protein was insufficient, its interaction with p53 triggered deficiencies and defects in other proteins that also have been found in patients with learning disabilities including autism.
Source: UCDavis
ScienceDaily (Aug. 9, 2012) — Manipulating a group of hormone-producing cells in the brain can control blood sugar levels in the body — a discovery that has dramatic potential for research into weight-loss drugs and diabetes treatment.
Erik Johnson uses the fruit fly, Drosophila, to look at an enzyme called AMP-activated kinase and its role in signaling the hormone that elevates the level of sugar in the blood. (Credit: Image courtesy of Wake Forest University)
In a paper published in the October issue of Genetics and available online now, neurobiologists at Wake Forest University examine how fruit flies (Drosophila) react when confronted with a decreased diet.
Reduced diet or starvation normally leads to hyperactivity in fruit flies — a hungry fly buzzes around feverishly, looking for more food. That happens because an enzyme called AMP-activated kinase stimulates the secretion of the adipokinetic hormone, which is the functional equivalent of glucagon. This hormone acts opposite of insulin, as it tells the body to release the sugar, or food, needed to fuel that hyperactivity. The body uses up its energy stores until it finds food.
But when Wake Forest’s Erik Johnson, an associate professor of biology, and his research team turned off AMP-activated kinase, the cells decreased sugar release and the hyperactive response stopped almost completely — even in the face of starvation.
"Since fruit flies and humans share 30 percent of the same genes and our brains are essentially wired the same way, it suggests that this discovery could inform metabolic research in general and diabetes research specifically," said Johnson, the study’s principal investigator. "The basic biophysical, biochemical makeup is the same. The difference in complexity is in the number of cells. Why flies are so simple is that they have approximately 100,000 neurons versus the approximately 11 billion in humans."
Medical advances as a result of this research might include:
• Diabetes research: Adipokinetic hormone is the insect equivalent to the hormone glucagon in the human pancreas. Glucagon raises blood sugar levels; insulin reduces them. However, it is difficult to study glucagon systems because the pancreatic cells are hard to pull apart. Studying how this similar system works in the fruit fly could pave the way to a drug that targets the cells that cause glucagon to tell the body to release sugar into the blood — thus reducing the need for insulin shots in diabetics.
• Weight-loss drugs: An “exercise drug” would turn on all AMP-activated kinase in the body and trick the body into thinking it was exercising. “Exercise stimulates AMP-activated kinase, so manipulation of this molecule may lead to getting the benefits of exercise without exercising,” Johnson said. In previous research published in the online journal PLoS ONE, Johnson and his colleagues found that, when you turn off AMP-activated kinase, you get fruit flies that “eat a lot more than normal flies, move around a lot less, and end up fatter.”
Source: Science Daily
THURSDAY, Aug. 9 (HealthDay News) — Researchers report that they have created a device able to short-circuit epileptic seizures in rats.
Similar in design to an implantable defibrillator, the device is placed in the brain and reacts only when a seizure starts to occur, essentially aborting the seizure’s electrical activity.
The self-adjusting device electrically stimulates the brain at the beginning of a short but frequent type of seizure in rats, and then automatically shuts itself off. The research was published in the Aug. 10 issue of the journal Science.
"It works like a ping-pong game," explained study author Dr. Gyorgy Buzsaki, a professor of neural science at New York University. "Every time a ball is coming your way, you apply an interfering pattern to whack it away."
Epilepsy is a brain disorder in which a person has repeated seizures over time. It affects nearly 3 million Americans, according to the Epilepsy Foundation, making it the third most common neurological disorder in the United States, after Alzheimer’s and stroke.
People with epilepsy can suffer from two different kinds of seizures: petit mal seizures, which last for just a few seconds but can occur frequently, and grand mal seizures, which are rare but involve violent muscle contractions and a loss of consciousness.
Seizures are episodes of disturbed brain activity that cause changes in attention or behavior. Brain cells keep firing instead of acting in an organized way. The malfunctioning electrical system of the brain causes surges of energy that can cause unconsciousness and muscle contractions.
The researchers tested the new device against petit mal seizures in rats because this type of seizure occurs hundreds of times a day. The sheer volume of the seizures allowed the scientists to effectively test the system they designed. People with petit mal seizures are typically treated effectively with drugs, so the device would not be used to treat that type of seizure.
In what Buzsaki describes as a simple, closed-loop system, the firing of brain neurons creates a spike in neurological activity that is followed by a wave and detected by the device, which fires back only when necessary. The system, called transcranial electrical stimulation, leaves other aspects of brain function unaffected. “The system doesn’t prevent seizures, it just treats them right away,” said Buzsaki. The stimulation reduced the length of a seizure by about 60 percent.
In humans, two plates about the size of a pocket watch could be placed in the skull in a position designed to target the affected area of the brain. The electrodes would be powered by ultralight electrical circuits implanted in the skull, Buzsaki explained.
The goal is to apply the system that worked in rats to people with complex partial seizures — epileptic seizures that affect both sides of the brain and cause a loss of consciousness, Buzsaki said. Although the device worked in rats, the results may not translate to humans.
This type of seizure also can occur with head injuries, brain infection and stroke. The cause is typically unknown.
In 20 percent to 40 percent of people who have complex partial seizures, drugs are ineffective and there are no remedies, Buzsaki said. “It’s not clear what kind of stimulation to deliver and where exactly in the brain the stimulation should go,” he explained.
Dr. Orrin Devinsky, director of the epilepsy program at New York University, said the research has enormous potential for treating epilepsy and other neurological problems. “What’s unique about this technique is that it’s a sophisticated way to identify the rhythmicity of the seizure itself and interrupt the cycle with precision,” he said. “Existing [deep brain stimulation] devices don’t finesse the timing this way.”
Devinsky, who was not associated with the study, said the research could potentially be applicable to people with tremors, Parkinson’s disease and even those with serious depression and other psychological disorders.
Source: HealthDay
August 9, 2012
MIT study reveals changes in brain activity as children learn to read other people’s behavior.
When you try to read other people’s thoughts, or guess why they are behaving a certain way, you employ a skill known as theory of mind. This skill, as measured by false-belief tests, takes time to develop: In children, it doesn’t start appearing until the age of 4 or 5.
Several years ago, MIT neuroscientist Rebecca Saxe showed that in adults, theory of mind is seated in a specific brain region known as the right temporo-parietal junction (TPJ). Saxe and colleagues at MIT have now shown how brain activity in the TPJ changes as children learn to reason about others’ thoughts and feelings.
The findings suggest that the right TPJ becomes more specific to theory of mind as children age, taking on adult patterns of activity over time. The researchers also showed that the more selectively the right TPJ is activated when children listen to stories about other people’s thoughts, the better those children perform in tasks that require theory of mind.
The paper, published in the July 31 online edition of the journal Child Development, lays the groundwork for exploring theory-of-mind impairments in autistic children, says Hyowon Gweon, a graduate student in Saxe’s lab and lead author of the paper.
“Given that we know this is what typically developing kids show, the next question to ask is how it compares to autistic children who exhibit marked impairments in their ability to think about other people’s minds,” Gweon says. “Do they show differences from typically developing kids in their neural activity?”
Saxe, an associate professor of brain and cognitive sciences and associate member of MIT’s McGovern Institute for Brain Research, is senior author of the Child Development paper. Other authors are Marina Bedny, a postdoc in Saxe’s lab, and David Dodell-Feder, a graduate student at Harvard University.
August 8, 2012
Researchers capture evolutionary dynamics in a new theoretical framework that could help explain some of the mysteries of how and why species change over time.
Although the qualitative description of evolution – its observed behavior and characteristics – is well-established, a comprehensive quantitative theory that captures general evolution dynamics is still lacking. There are also many lingering mysteries surrounding the story of life on Earth, including the question of why sex is such a prevalent reproductive strategy. A team of scientists from the Chinese Academy of Sciences; Jilin University in Jilin, China; and the State University of New York at Stony Brook, led by Prof. Jin Wang, has examined some of these puzzles from a physical science prospective. They propose a new theory of evolution with two ingredients: the underlying emergent “fitness” landscape and an associated evolutionary force called “curl flux,” which causes species to move through the emergent fitness landscape in a spiraling manner.
The researchers captured evolutionary relationships in a system of equations. They then created quantitative pictures that visualized evolutionary pathways as journeys through a mountainous terrain of peaks and valleys of biological fitness. The key breakthrough beyond the conventional quantitative theory of evolution is the emergent curl flux, which is generated by interactions between individuals within or across species. The underlying emergent landscape gradient and the curl flux act together as a “Yin and Yang” duality pair to determine the dynamics of general evolution, says Wang. An example of similar behavior is the particle and wave duality that determines the dynamics of the quantum world, he notes. The researchers also note that this combined effect is analogous to the way electric and magnetic forces both act on electrons.
The new theory provides a physical foundation for general evolution dynamics. The researchers found that interactions between individuals of different species can give rise to the curl flux. This can sustain an endless evolution that does not lead to areas of higher relative fitness, even if the physical environment is unchanged.
This finding offers a theoretical framework to explain the Red Queen Hypothesis, which states that species continually evolve in order to fend off parasites that are themselves continually evolving. The hypothesis, first proposed by evolutionary biologist Leigh Van Valen in 1973, gets its name from the character of the Red Queen in Lewis Carroll’s book Through the Looking-Glass, who observed that in her world it was necessary to keep running just to stay in one place. The idea of endless co-evolution through the maintenance of the genetic variation due to the curl flux could help explain the benefits of sexual reproduction, since the mixing and matching of genes preserves a greater diversity of traits. When a species’ arms race with a co-evolving parasite takes an unexpected twist, a previously unnecessary trait could suddenly turn into the key to surviving. In the co-evolving world, there is no guarantee for “survival of the fittest” and it is often necessary to keep running for survival.
Source: PHYS.ORG
August 8, 2012 By Lia Samson
(Phys.org) — In a recent paper, Aleksander Ellis of the University of Arizona Eller College of Management and a colleague demonstrate that lack of sleep can cause deviant behavior at work.
Early 2011 saw a spate of reports in the media about air traffic controllers sleeping on the job as a result of sleep deprivation. The potential harm from this behavior is obvious, but what about the average office job? Can sleep deprivation cause counterproductive, or even unethical, behavior in organizations?
“Over the past decade, Americans have been getting less and less sleep, and estimates are that this trend will continue,” said Professor of Management and Organizations Aleksander Ellis, the Charles and Candice Nelson Fellow. “In fact, in certain industries, lack of sleep is worn as a badge of honor.”
In a recent paper published in the Academy of Management Journal, Ellis and co-author Michael Christian of Kenan-Flagler Business School at the University of North Carolina-Chapel Hill demonstrate that lack of sleep can cause deviant behavior.
In one part of the study, for instance, the researchers asked a group of subjects to respond to an email that contained colloquial language and misspellings. One of the sleep-deprived subjects responded with an unprofessional, personal attack. This is just one example Ellis and Christian cite to demonstrate how sleep deprivation reduces self-control and increases hostility.
Ellis and Christian are currently working on a parallel project that examines how sleep deprivation affects the tendency of individuals to behave unethically by conforming to the behavior of unethical authority figures.
Source: PHYS.ORG
August 8th, 2012
The brain has billions of neurons, arranged in complex circuits that allow us to perceive the world, control our movements and make decisions. Deciphering those circuits is critical to understanding how the brain works and what goes wrong in neurological disorders.
MIT neuroscientists have now taken a major step toward that goal. In a new paper appearing in the Aug. 9 issue of Nature, they report that two major classes of brain cells repress neural activity in specific mathematical ways: One type subtracts from overall activation, while the other divides it.
“These are very simple but profound computations,” says Mriganka Sur, the Paul E. Newton Professor of Neuroscience and senior author of the Nature paper. “The major challenge for neuroscience is to conceptualize massive amounts of data into a framework that can be put into the language of computation. It had been a mystery how these different cell types achieve that.”
Neuroscientists report that two major classes of brain cells repress neural activity in specific mathematical ways: One type subtracts from overall activation, while the other divides it.
The findings could help scientists learn more about diseases thought to be caused by imbalances in brain inhibition and excitation, including autism, schizophrenia and bipolar disorder.
Lead authors of the paper are grad student Caroline Runyan and postdoc Nathan Wilson. Forea Wang ’11, who contributed to the work as an MIT undergraduate, is also an author of the paper.
A fine balance
There are hundreds of different types of neuron in the brain; most are excitatory, while a smaller fraction are inhibitory. All sensory processing and cognitive function arises from the delicate balance between these two influences. Imbalances in excitation and inhibition have been associated with schizophrenia and autism.
“There is growing evidence that alterations in excitation and inhibition are at the core of many subsets of neuropsychiatric disorders,” says Sur, who is also the director of the Simons Center for the Social Brain at MIT. “It makes sense, because these are not disorders in the fundamental way in which the brain is built. They’re subtle disorders in brain circuitry and they affect very specific brain systems, such as the social brain.”
In the new Nature study, the researchers investigated the two major classes of inhibitory neurons. One, known as parvalbumin-expressing (PV) interneurons, targets neurons’ cell bodies. The other, known as somatostatin-expressing (SOM) interneurons, targets dendrites — small, branching projections of other neurons. Both PV and SOM cells inhibit a type of neuron known as pyramidal cells.
To study how these neurons exert their influence, the researchers had to develop a way to specifically activate PV or SOM neurons, then observe the reactions of the target pyramidal cells, all in the living brain.
First, the researchers genetically programmed either PV or SOM cells in mice to produce a light-sensitive protein called channelrhodopsin. When embedded in neurons’ cell membranes, channelrhodopsin controls the flow of ions in and out of the neurons, altering their electrical activity. This allows the researchers to stimulate the neurons by shining light on them.
The team combined this with calcium imaging inside the target pyramidal cells. Calcium levels reflect a cell’s electrical activity, allowing the researchers to determine how much activity was repressed by the inhibitory cells.
“Up until maybe three years ago, you could only just blindly record from whatever cell you ran into in the brain, but now we can actually target our recording and our manipulation to well-defined cell classes,” Runyan says.
Taking a circuit apart
In this study, the researchers wanted to see how activation of these inhibitory neurons would influence how the brain processes visual input — in this case, horizontal, vertical or tilted bars. When such a stimulus is presented, individual cells in the eye respond to points of light, then convey that information to the thalamus, which relays it to the visual cortex. The information stays spatially encoded as it travels through the brain, so a horizontal bar will activate corresponding rows of cells in the brain.
Those cells also receive inhibitory signals, which help to fine-tune their response and prevent overstimulation. The MIT team found that these inhibitory signals have two distinct effects: Inhibition by SOM neurons subtracts from the total amount of activity in the target cells, while inhibition by PV neurons divides the total amount of activity in the target cells.
“Now that we finally have the technology to take the circuit apart, we can see what each of the components do, and we found that there may be a profound logic to how these networks are naturally designed,” Wilson says.
These two types of inhibition also have different effects on the range of cell responses. Every sensory neuron responds only to a particular subset of stimuli, such as a range of brightness or a location. When activity is divided by PV inhibition, the target cell still responds to the same range of inputs. However, with subtraction by SOM inhibition, the range of inputs to which cells will respond becomes narrower, making the cell more selective.
Increased inhibition by PV neurons also changes a trait known as the response gain — a measurement of how much cells respond to changes in contrast. Inhibition by SOM neurons does not alter the response gain.
The researchers believe this type of circuit is likely repeated throughout the brain and is involved in other types of sensory perception, as well as higher cognitive functions.
Sur’s lab now plans to study the role of PV and SOM inhibitory neurons in a mouse model of autism. These mice lack a gene called MeCP2, giving rise to Rett Syndrome, a rare disease that produces autism-like symptoms as well as other neurological and physical impairments. Using their new technology, the researchers plan to test the hypothesis that a lack of neuronal inhibition underlies the disease.
Source: Neuroscience News
ScienceDaily (Aug. 8, 2012) — Stressed and non-stressed people use different brain regions and different strategies when learning. This has been reported by the cognitive psychologists PD Dr. Lars Schwabe and Professor Oliver Wolf from the Ruhr-Universität Bochum in the Journal of Neuroscience. Non-stressed individuals applied a deliberate learning strategy, while stressed subjects relied more on their gut feeling. “These results demonstrate for the first time that stress has an influence on which of the different memory systems the brain turns on,” said Lars Schwabe.
The experiment: Stress due to ice-water
The data from 59 subjects were included in the study. Half of the participants had to immerse one hand into ice-cold water for three minutes under video surveillance. This stressed the subjects, as hormone assays showed. The other participants had to immerse one of their hands just in warm water. Then both the stressed and non-stressed individuals completed the so-called weather prediction task. The subjects looked at playing cards with different symbols and learned to predict which combinations of cards announced rain and which sunshine. Each combination of cards was associated with a certain probability of good or bad weather. People apply differently complex strategies in order to master the task. During the weather prediction task, the researchers recorded the brain activity with MRI.
Two routes to success
Both stressed and non-stressed subjects learned to predict the weather according to the symbols. Non-stressed participants focused on individual symbols and not on combinations of symbols. They consciously pursued a simple strategy. The MRI data showed that they activated a brain region in the medial temporal lobe — the hippocampus, which is important for long-term memory. Stressed subjects, on the other hand, applied a more complex strategy. They made their decisions based on the combination of symbols. They did this, however, subconsciously, i.e. they were not able to formulate their strategy in words. The result of the brain scans was also accordingly: In the case of the stressed volunteers the so-called striatum in the mid-brain was activated — a brain region that is responsible for more unconscious learning. “Stress interferes with conscious, purposeful learning, which is dependent upon the hippocampus,” concluded Lars Schwabe. “So that makes the brain use other resources. In the case of stress, the striatum controls behaviour — which saves the learning achievement.”
Source: Science Daily
8-Aug-2012
The molecular missteps that disrupt brain function in the most common form of adult-onset muscular dystrophy have been revealed in a new study published by Cell Press. Myotonic dystrophy is marked by progressive muscle wasting and weakness, as well as excessive daytime sleepiness, memory problems, and mental retardation. A new mouse model reported in the August 9 issue of the journal Neuron reproduces key cognitive and behavioral symptoms of this disease and could be used to develop drug treatments, which are currently lacking.
The red dots are the toxic RNAs accumulating in the nucleus (blue) of a myotonic dystrophy cell (these are induced pluripotent stem, or iPS, cells) and the green is a neuronal marker. Credit: Charizanis et al., Neuron.
"The new animal model reproduces important aspects of myotonic dystrophy brain disease, so this model may be useful to develop biomarkers and test future drug therapies," says senior study author Maurice Swanson of the University of Florida.
Previous studies had shown that mutated genes underlying the disease produce toxic ribonucleic acids (RNAs) during transcription, and these RNAs cause the production of incorrect forms of proteins in muscle tissue by blocking the actions of a protein called MBNL1. As a result, proteins typically found in fetal muscles increase in abundance, while the normal suite of proteins found in adult muscles decrease in number. However, until now, it was not clear whether molecular abnormalities similar to those in muscle tissue of individuals with mytonic dystrophy also occur in the brain, resulting in the cognitive neurological problems.
In the new study, Swanson and his team focused on a related protein called MBNL2, which is found in the brain. They developed a new mouse model that lacked a functional Mbnl2 gene. These animals experienced an increase in the amount of rapid eye movement sleep as well as learning and memory deficits, similar to human patients.
The researchers also found extensive evidence of toxic RNAs in the hippocampus, as well as signs that fetal proteins were being produced in the brains of adult mutants. This pattern was also evident in the autopsied brain tissue of humans who had myotonic dystrophy. “This study should accelerate our understanding of how myotonic dystrophy mutations impact brain development and function,” Swanson says.
Source: EurekAlert!
By Lisa Cosgrove | August 7, 2012
It is part of the human condition to have implicit biases—and remain blissfully ignorant of them. Academic researchers, scientists, and clinicians are no exception; they are as marvelously flawed as everyone else. But it is not the cognitive bias that’s the problem. Rather, the denial that there is a problem is where the issues arise. Indeed, our capacity for self-deception was beautifully captured in the title of a recent book addressing researchers’ self-justificatory strategies, Mistakes Were Made (But Not by Me).
Illustration by Dusan Petricic
Decades of research have demonstrated that cognitive biases are commonplace and very difficult to eradicate, and more recent studies suggest that disclosure of financial conflicts of interest may actually worsen bias. This is because bias is most often manifested in subtle ways unbeknownst to the researcher or clinician, and thus is usually implicit and unintentional. For example, although there was no research misconduct or fraud, re-evaluations of liver tissue of rats exposed to the drug dioxin resulted in different conclusions about the liver cancer in those rats: compared to the original investigation, an industry-sponsored re-evaluation identified fewer tissue slides as cancerous and this finding affected policy recommendations (water quality standards were weakened). (See also Brown, Cold Spring Harbor Laboratory Press, 13–28, 1991.) This example is just one of many that points to a genericrisk that a financial conflict of interest may compromise research or undermine public trust.
Indeed, recent neuroscience investigations demonstrate that effective decision-making involves not just cognitive centers but also emotional areas such as the hippocampus and amygdala. This interplay of cognitive-emotional processing allows conflicts of interest to affect decision-making in a way that is hidden from the person making the decision.
Despite these findings, many individuals are dismissive of the idea that researchers’ financial ties to industry are problematic. For example, in a recent essay in The Scientist, Thomas Stossel of Brigham & Women’s Hospital and Harvard Medical School asked, “How could unrestricted grants, ideal for research that follows up serendipitous findings, possibly be problematic? The money leads to better research that can benefit patients.” Many argue that subjectivity in the research process and the potential for bias can be eradicated by strict adherence to the scientific method and transparency about industry relationships. Together, scientists believe, these practices can guarantee evidence-based research that leads to the discovery and dissemination of “objective” scientific truths. The assumption is that the reporting of biased results is a “bad apple” problem—a few corrupt individuals engaging in research fraud. But what we have today is a bad barrel.
Some have begun to use the analytic framework of “institutional corruption” to bring attention to the fact that the trouble is not with a few corrupt individuals hurting an organization whose integrity is basically intact. Institutional corruption refers to the systemic and usually legal—and often accepted and widely defended—practices that bring an organization or institution off course, undermine its mission and effectiveness, and weaken public trust. Although the entire field of biomedicine has come under scrutiny because of concerns about an improper dependence on industry and all medical specialties have struggled with financial conflicts of interest, psychiatry has been particularly troubled, being described by some as having a crisis of credibility.
This credibility crisis has been played out most noticeably in the public controversy surrounding the latest revision to the Diagnostic and Statistical Manual of Mental Disorders (DSM). The DSM is often referred to as the “Bible” of mental disorders, and is produced by the American Psychiatric Association (APA), a professional organization with a long history of industry ties. DSM-5, the revised edition scheduled for publication in May, 2013, has already been criticized for “disease mongering,” or pathologizing normal behavior. Concerns have been raised that because the individuals responsible for making changes and adding new disorders have strong and long-standing financial associations to pharmaceutical companies that manufacture the drugs used to treat these disorders, the revision process may be compromised by undue industry influence.
Researchers, clinicians, and psychiatrists who served on the DSM-IV have pointed out that adding new disorders or lowering the diagnostic threshold of previously included disorders may create “false positives,” individuals incorrectly identified as having a mental disorder and prescribed psychotropic medication. For example, there was a heated debate about pathologizing the normal grieving process if DSM-5 eliminated the bereavement exclusion for major depressive disorder (MDD). The concern was that widening the diagnostic boundaries of depression to include grief as a “qualifying event,” thereby allowing for a diagnosis of MDD just 2 weeks after the loss of a loved one, would falsely identify individuals as depressed. Although it is not the APA’s intent to play handmaiden to industry, the reality is that such a change would result in more people being prescribed antidepressants following the loss of a loved one. In fact, psychiatrist Allen Frances, who chaired the DSM-IV task force, has noted that DSM-5 would be a “bonanza” for drug companies.
After receiving criticism about potential bias in the development of the DSM-IV, the APA required that DSM-5 panel members file financial disclosures. Additionally, during their tenure on the panels they were not allowed to receive more than $10,000 from pharmaceutical companies or have more than $50,000 in stock holdings in pharmaceutical companies (unrestricted research grants were excluded from this policy). The majority of diagnostic panels, however, continue to have the majority of their members with financial ties to the pharmaceutical industry. Specifically, 67 percent of the 12-person panel for mood disorders, 83 percent of the 12-person panel for psychotic disorders, and all 7 members of the sleep/wake disorders panel (which now includes ‘‘Restless Leg Syndrome’’) have ties to the pharmaceutical companies that manufacture the medications used to treat these disorders or to companies that service the pharmaceutical industry.
Clearly, the new disclosure policy has not been accompanied by any reduction in the financial conflicts of interest of DSM panel members. Moreover, Darrel Regier, speaking on behalf of the APA and in defense of DSM panel members with industry ties, told USA Today. “There’s this assumption that a tie with a company is evidence of bias. But these people can be objective.” However, as science has repeatedly shown, transparency alone cannot mitigate bias and is an insufficient solution for protecting the integrity of the revision process. Objectivity is not a product that can be easily secured by adherence to the scientific method. Rather, there is a generic risk that a conflict of interest may result in implicit, unintentional bias. Similarly, as Sinclair Lewis said, “It is difficult to get a man to understand something when his salary depends upon his not understanding it.”
Source: TheScientist
7 August 2012
New NeuRA research shows that the brains of people with schizophrenia may attempt to repair damage caused by the disease, in another example of the adult brain’s capacity to change and grow.
Prof Cyndi Shannon Weickert, Dr Dipesh Joshi and colleagues from Neuroscience Research Australia studied the brains of people with schizophrenia and focussed on one of the hardest-hit regions, the orbitofrontal cortex, which is the part of the brain involved in regulating emotional and social behaviour.
Most neurons – brain cells that transmit information – are found in tissue near the surface of the brain. However, in the brains of people with schizophrenia, the team found a high density of neurons in deeper areas.
“For over a decade we’ve known about the high density of neurons in deeper brain tissue in people with schizophrenia. Researchers thought these neurons were simply forgotten by the brain, and somehow didn’t die off like they do during development in healthy people,” says Prof Shannon Weickert.
“What we now have is evidence that suggests these neurons are derived from the part of the brain that produces new neurons, and that they may be in the process of moving. We can’t be sure where they are moving to, but given their location it is likely they are on their way to the surface of the brain, the area most affected by schizophrenia,” Prof Shannon Weickert concluded.
How was this study done?