Posts tagged neuroscience

Signs of autism—such as impaired social skills and repetitive, ritualistic movements—usually begin to appear when a child is about 18 months old. Autism is thought to result from miswired connections in the developing brain, and many experts believe that therapies must begin during a “critical window,” before the faulty circuits become fixed in place. But a new study online today in Science shows that at least one malfunctioning circuit can be repaired after that window closes, holding out hope that in some forms of autism, abnormal circuits in the brain can be corrected even after their development is complete.

Faulty wiring. Shutting off the Nlgn3 gene in mice (right panel) results in miswired synaptic connections, which may be fixable. Credit: S. J. Baudouin et al., Science

According to developmental neurobiologist Peter Scheiffele of the University of Basel in Switzerland, autism doesn’t result from a handful of “culprit” genes that point to a treatable flaw. Instead, patients appear to carry mutations in one out of dozens, even hundreds of risk genes. “This genetic complexity is a huge issue with respect to developing treatments [for autism],” Scheiffele says. To complicate the picture further, autism is not always an isolated disorder; it’s often a common feature in syndromes that otherwise differ drastically. For example, in fragile X syndrome, a form of mental retardation, about 25% of patients are also autistic.

Scheiffele and colleagues were studying a gene called neuroligin-3 (Nlgn3), involved in building the contact points, called synapses, between neurons. Many researchers believe that autism begins at the synapse, and mutations in Nlgn3 have appeared in some forms of the disorder. Sheiffele’s team was focusing on synapses in the cerebellum, a part of the brain that controls movement, but, according to recent research, may also be involved in social behavior. Abnormalities in this region may contribute to both the unusual movements and the social problems seen in autistic patients.

To get a better handle on the role of Nlgn3, the scientists studied mice whose Nlgn3 genes were engineered with an on-off switch, called a promoter region, that is controlled by the antibiotic doxycycline. The animals were raised with the drug in their drinking water, which kept the switch in the off position. With the Nlgn3 gene disabled in the mice, neurons in their cerebellum made the abnormal connections seen in the autistic brain.

Specifically, and much to the researchers’ surprise, the lack of Nlgn3 led to the overactivation of a receptor abbreviated as mGluR1α. This receptor is a component of a pathway that is also disrupted in fragile X syndrome, though it results from mutations in an entirely different gene. In the mice, the overabundance of these receptors led the neurons to make synaptic connections in the wrong places.

To see if turning Nlgn3 gene back on would correct these problems, the researchers withdrew the doxycycline. It worked: With Nlgn3 functioning once more, levels of the extraneous receptor receded back to normal, and the misplaced synapses began to disappear.

"Our finding demonstrates that there is still flexibility after the ‘critical window’ of brain development,” Scheiffele says. “It raises the question: To what extent can a miswired brain be corrected?” The next step, he says, is to see whether motor abnormalities, such as ladder-climbing difficulties, and social interactions can be corrected with similar treatment in the engineered mice. His team is also studying whether drugs that block the mGluR1α receptor can have the same effect as genetically controlling the Nlgn3 gene, which isn’t a treatment option for humans.

"This study holds out hope for children and even adults with developmental disorders. Maybe their conditions aren’t set in stone and can be treated," says neuroscientist Kimberly Huber of the University of Texas Southwestern Medical Center in Dallas. Huber adds that drugs that block a similar receptor, mGluR5, are in clinical trials to treat fragile X syndrome.

(Source: news.sciencemag.org)

Moderate exercise may help people cope with anxiety and stress for an extended period of time post-workout, according to a study by kinesiology researchers in the University of Maryland School of Public Health published in the journal Medicine and Science in Sports and Exercise.

"While it is well-known that exercise improves mood, among other benefits, not as much is known about the potency of exercise’s impact on emotional state and whether these positive effects endure when we’re faced with everyday stressors once we leave the gym," explains J. Carson Smith, assistant professor in the Department of Kinesiology. "We found that exercise helps to buffer the effects of emotional exposure. If you exercise, you’ll not only reduce your anxiety, but you’ll be better able to maintain that reduced anxiety when confronted with emotional events."

Smith, whose research explores how exercise and physical activity affect brain function, aging and mental health, compared how moderate intensity cycling versus a period of quiet rest (both for 30 minutes) affected anxiety levels in a group of healthy college students. He assessed their anxiety state before the period of activity (or rest), shortly afterward (15 minutes after) and finally after exposing them to a variety of highly arousing pleasant and unpleasant photographs, as well as neutral images. At each point, study participants answered 20 questions from the State-Trait Anxiety inventory, which is designed to assess different symptoms of anxiety. All participants were put through both the exercise and the rest states (on different days) and tested for anxiety levels pre-exercise, post-exercise, and post-picture viewing.

Smith found that exercise and quiet rest were equally effective at reducing anxiety levels initially. However, once they were emotionally stimulated (by being shown 90 photographs from the International Affective Picture System, a database of photographs used in emotion research) for ~20 minutes, the anxiety levels of those who had simply rested went back up to their initial levels, whereas those who had exercised maintained their reduced anxiety levels.

"The set of photographic stimuli we used from the IAPS database was designed to simulate the range of emotional events you might experience in daily life," Smith explains. "They represent pleasant emotional events, neutral events and unpleasant events or stimuli. These vary from pictures of babies, families, puppies and appetizing food items, to very neutral things like plates, cups, furniture and city landscapes, to very unpleasant images of violence, mutilations and other gruesome things."

The study findings suggest that exercise may play an important role in helping people to better endure life’s daily anxieties and stressors.

Smith plans to explore if exercise could have the same persistent beneficial effect in patients who regularly experience anxiety and depression symptoms. In collaboration with the new Maryland Neuroimaging Center, he is also exploring the addition of functional magnetic resonance imaging, or fMRI, to measure brain activity during the period of exposure to emotionally stimulating images to see how exercise may alter the brain’s emotion-related neural networks.

Smith also investigates the role of exercise in preventing cognitive decline in older adults. His research has shown that physical activity promotes changes in the brain that may protect those at high risk for Alzheimer’s disease.

(Source: newsdesk.umd.edu)

Stress has long been pegged as the enemy of attention, disrupting focus and doing substantial damage to working memory — the short-term juggling of information that allows us to do all the little things that make us productive.

By watching individual neurons at work, a group of psychologists at the University of Wisconsin-Madison has revealed just how stress can addle the mind, as well as how neurons in the brain’s prefrontal cortex help “remember” information in the first place.

Working memory is short-term and flexible, allowing the brain to hold a large amount of information close at hand to perform complex tasks. Without it, you would have forgotten the first half of this sentence while reading the second half. The prefrontal cortex is vital to working memory.

"In many respects, you’d look pretty normal without a prefrontal cortex," said Craig Berridge, UW-Madison psychology professor. "You don’t need that part of the brain to hear or talk, to keep long-term memories, or to remember what you did as a child or what you read in the newspaper three days ago."

But without your prefrontal cortex you’d be unable to stay on task or modulate your emotions well.

"People without a prefrontal cortex are very distractible," Berridge said. "They’re very impulsive. They can be very argumentative."

The neurons of the prefrontal cortex help store information for short periods. Like a chalkboard, these neurons can be written with information, erased when that information is no longer needed, and rewritten with something new.

It’s how the neurons maintain access to that short-term information that leaves them vulnerable to stress. David Devilbiss, a scientist working with Berridge and lead author on a study published today in the journal PLOS Computational Biology, applied a new statistical modeling approach to show that rat prefrontal neurons were firing and re-firing to keep recently stored information fresh.

"Even though these neurons communicate on a scale of every thousandth of a second, they know what they did one second to one-and-a-half seconds ago," Devilbiss said. "But if the neuron doesn’t stimulate itself again within a little more than a second, it’s lost that information."

Apply some stress — in the researchers’ case, a loud blast of white noise in the presence of rats working on a maze designed to test working memory — and many neurons are distracted from reminding themselves of … what was it we were doing again?

"We’re simultaneously watching dozens of individual neurons firing in the rats’ brains, and under stress those neurons get even more active," said Devilbiss, whose work was supported by the National Science Foundation and National Institutes of Health. "But what they’re doing is not retaining information important to completing the maze. They’re reacting to other things, less useful things."

Without the roar of white noise, which has been shown to impair rats in the same way it does monkeys and humans, the maze-runners were reaching their goal about 90 percent of the time. Under stress, the animals completed the test at a 65 percent clip, with many struggling enough to fall to blind chance.

Recordings of the electrical activity of prefrontal cortex neurons in the maze-running rats showed these neurons were unable to hold information key to finding the next chocolate chip reward. Instead, the neurons were frenetic, reacting to distractions such as noises and smells in the room.

The effects of stress-related distraction are well-known and dangerous.

"The literature tells us that stress plays a role in more than half of all workplace accidents, and a lot of people have to work under what we would consider a great deal of stress," Devilbiss said. "Air traffic controllers need to concentrate and focus with a lot riding on their actions. People in the military have to carry out these thought processes in conditions that would be very distracting, and now we know that this distraction is happening at the level of individual cells in the brain."

The researchers’ work may suggest new directions for treatment of prefrontal cortex dysfunction.

"Based on drug studies, it had been believed stress simply suppressed prefrontal cortex activity," Berridge said. "These studies demonstrate that rather than suppressing activity, stress modifies the nature of that activity. Treatments that keep neurons on their self-stimulating task while shutting out distractions may help protect working memory."

(Source: news.wisc.edu)

Looking at a tangled mass of network cables plugged into a crowded router doesn’t yield much insight into the network traffic that runs through the hardware.

Similarly, Lynn H. Matthias Professor of Electrical and Computer Engineering Barry Van Veen says that looking at the three pounds of interwoven neurons that make up the hardware of the human brain doesn’t give the complete picture of the brain activity that supports human cognition and consciousness.

Working with multiple collaborators, Van Veen has applied signal analysis techniques to the electric or magnetic fields measured noninvasively at the scalp through electroencephalography (EEG) or magnetoencephalography (MEG) to develop methods for identifying network models of brain function — essentially, traffic patterns of neural activity present in the human brain.

"It’s analogous to coming up with a new microscope," says Van Veen.

Having a reliable traffic map of normal brain function provides a baseline for comparison for understanding how different disorders, substances and devices affect the brain. “Now that we’ve got the tool ready, the opportunities to try it out on scientifically interesting questions are really blossoming,” says Van Veen.

For instance, network models may provide a better blueprint for how medical devices can interface with the brain. Van Veen recently began working with biomedical engineering Associate Professor Justin Williams to apply his work toward making better brain-machine interfaces.

But the implications of network models go beyond engineering questions. The effect of alcohol on the brain just begs for network analysis, according to Van Veen. The network model could allow researchers to see precisely which parts of the brain are altered by alcohol consumption. It could provide insight into how short-term memory works, help explain the effects of schizophrenia and monitor treatment, help measure the depth and effectiveness of different types of anesthesia, and even help give insight into the brain activity that precedes — or prevents — a miraculous recovery from a coma.

"We’re developing this tool as a significant improvement over what people have had access to before," says Van Veen. "The possibilities for using it to study different aspects of brain function are nearly unlimited."

(Source: news.wisc.edu)