Monday, November 22, 2010

NONINVASIVE BRAIN STIMULATION HELPS IMPROVE MOTOR FUNCTION IN STROKE PATIENTS

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A noninvasive electric stimulation technique administered to both sides of the brain can help stroke patients who have lost motor skills in their hands and arms, according to a new study led by researchers at Beth Israel Deaconess Medical Center (BIDMC).

Described in the Online Issue of the journal Neurology, the findings showed that stroke patients who received bihemispheric transcranial direct current stimulation (tDCS) coupled with a regimen of physical and occupational therapy had a three-fold greater improvement in motor function compared with patients who received only physical/occupational rehabilitation and a placebo form of stimulation.

"We think that the key to this therapy's success in improving stroke patients' motor function is based on its ability to affect the brain activity on both the stroke-affected side of the brain and the healthy side of the brain as patients work to re-learn lost motor skills," says senior author Gottfried Schlaug, MD, PhD, the Director of the Stroke Service in BIDMC's Department of Neurology and Associate Professor of Neurology at Harvard Medical School.

In the brain of a healthy individual, the left and right sides of the motor cortex work in tandem, inhibiting one another as needed in order to successfully carry out such one-sided movements as writing or teeth-brushing. But, explains lead author Robert Lindenberg, MD, an HMS Instructor of Neurology at BIDMC, when a person suffers a stroke (as might happen when an artery to the brain is blocked by a blood clot or atherosclerotic deposit) the interaction between the two sides of the brain involved in motor skills changes.

"As a result," he explains, "the motor region on the unaffected side of the brain begins to exert an unbalanced effect onto the motor region of the brain's damaged side." And, as Schlaug and Lindenberg further explain, this leads to an increased inhibition of the stroke-damaged motor region, as the remaining intact portions of this region try to increase activity in the motor pathways to facilitate recovery.

tDCS is an experimental therapy in which a small electrical current is passed to the brain through the scalp and skull. Because previous studies had determined that tDCS could improve motor function if applied to either the damaged or undamaged side of the brain, Schlaug's team hypothesized that applying tDCS to both sides – while simultaneously engaging the stroke patient in motor skill relearning activities – would further speed the recovery process.

"tDCS works by modulating regional brain activity," explains Schlaug. "In applying this therapy to both hemispheres of the brain, we used one direction of current to increase brain activity on the damaged side, and used the reverse current to inhibit brain activity on the healthy side, thereby rebalancing the interactions of both sides of the brain."

Schlaug and his collaborators studied 20 patients who had suffered an ischemic stroke at least five months prior to the onset of the study. Participants were separated into two groups: Half of the subjects received a 30-minute daily treatment session of electrical stimulation, while the other half received a "sham" placebo treatment designed to mimic electrical stimulation. Both groups of patients concurrently received 60 minutes of occupational and physical therapy. The treatment was repeated daily for five days.

By using sophisticated MRI (magnetic resonance imaging) techniques, the researchers were able to "map" the positions of the stroke lesions in relation to the brain's motor system. "This helped us to very closely match the two patient groups," notes Schlaug. "Not only did the two groups of patients outwardly exhibit similar motor impairments, but we could tell from the MRIs that their lesions were positioned in similar areas of the brain. This novel approach strengthens the results, since no other between-group factor could explain the therapy's effects."

The results showed that the patients treated with tDCS exhibited a three-fold improvement in motor outcomes, such as an improved ability to grasp or perform wrist and finger movements, compared with patients who underwent physical and occupational therapy coupled with placebo stimulation. In addition, functional brain imaging showed that the therapy's effect was correlated with increased activity of the brain's non-damaged motor parts on the side of the stroke hemisphere.

"This is the first time that stimulation therapy has been administered simultaneously to both brain hemispheres and coupled with physical/occupational therapy," explains Schlaug. "Both sides of the brain play a role in recovery of function [following a stroke] and the combination of peripheral sensorimotor activities and central brain stimulation increases the brain's ability to strengthen existing connections and form new connections. It is a testament of just how plastic the brain can be if novel and innovative therapies are applied using our current knowledge of brain function."

Beth Israel Deaconess Medical Center (BIDMC).

SHARKS AND WOLVES: PREDATOR, PREY INTERACTIONS SIMILAR ON LAND AND IN OCEANS

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There may be many similarities between the importance of large predators in marine and terrestrial environments, researchers concluded in a recent study, which examined the interactions between wolves and elk in the United States, as well as sharks and dugongs in Australia.

In each case, the major predators help control the populations of their prey, scientists said. But through what’s been called the “ecology of fear” they also affect the behavior of the prey, with ripple impacts on other aspects of the ecosystem and an ecological significance that goes far beyond these species.

The study was done by scientists from Oregon State University and the University of Washington, and was published in Frontiers in Ecology and the Environment, a professional journal.

“For too long we’ve looked at ecosystem functions on land and in the oceans as if they were completely separate,” said William Ripple, a professor in the Department of Forest Ecosystems at Society at OSU, and an international expert in the study of large predators such as wolves and cougars.

“We’re now finding that there are many more similarities between marine and terrestrial ecosystems than we’ve realized,” Ripple said. “We need to better understand these commonalities, and from them learn how interactions on land may be a predictor of what we will see in the oceans, and vice versa.”

In this study, Ripple and collaborator Aaron Wirsing, a researcher with the School of Forest Resources at the University of Washington, compared what has been learned about wolf and elk interaction in Yellowstone National Park in the U.S. to the interplay of tiger sharks and dugongs in Shark Bay, Australia. Dugongs are large marine mammals, similar to manatees, that feed primarily on seagrasses and are a common prey of sharks.

In studies with elk, scientists have found that the presence of wolves alters their behavior almost constantly, as they try to avoid encounters, leave room for escape and are constantly vigilant. The elk graze less in sensitive habitats, which in Yellowstone is helping streamside shrubs and aspen trees to recover, along with other positive impacts on beaver dams and wildlife.

Conceptually similar activities are taking place between sharks and dugongs, the researchers found. When sharks are abundant, dugongs graze less in shallow water where they are most vulnerable to sharks, and sacrifice food they might otherwise consume. This allows the seagrass meadows to thrive, along with the range of other plant and marine animal species that depend on them.

Related marine interactions have been observed in the North Atlantic Ocean, Ripple said. As shark populations were diminished by overfishing, the number of rays increased, which in turn reduced the level of sea scallops, an important fishery.

The marine/terrestrial similarities are also reflected in the body condition and health of species, the researchers noted. In Shark Bay, green sea turtles are more willing to face risks from sharks and seek the best grazing areas when their body condition is strong. In like fashion, the common wildebeest on the African Serengeti are less vulnerable to attack by lions or hyenas when their physical condition is good.

A more frequent information exchange between terrestrial and marine ecologists could provide additional insights into ecosystem function, the researchers said in their report.

(Photo: Oregon S.U.)

Oregon State University

UNIVERSITY RESEARCH REVEALS DEAF ADULTS SEE BETTER THAN HEARING PEOPLE

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Adults born deaf react more quickly to objects at the edge of their visual field than hearing people, according to groundbreaking new research by the University of Sheffield.

The study, which was funded by the Royal National Institute for Deaf People (RNID), has, for the first time ever, seen scientists test how peripheral vision develops in deaf people from childhood to adulthood.

Dr Charlotte Codina, from the University's Academic Unit of Ophthalmology and Orthoptics, led the research and found that children born deaf are slower to react to objects in their peripheral vision compared to hearing children. However, deaf adolescents and adults who have been without hearing since birth can react to objects in their peripheral vision more quickly.

The findings of Dr Codina's study, which were published in Development Science (Thursday 11 November 2010), showed that deaf children aged between five to 10 years old had a slower reaction time to light stimuli in their peripheral vision than hearing children of the same age. By the age of 11 and 12 however, hearing and deaf children react equally quickly and deaf adolescents between 13 and 15 reacted more quickly than their hearing peers.

The study tested profoundly deaf children (aged five to 15 years) using a self-designed visual field test, and compared this to age-matched hearing controls as well as to deaf and hearing adult data.

The children tested sat with their head positioned in the centre of a grey acrylic hemisphere into which 96 LEDs were implanted. The participants then had to watch a central glowing ring in which a camera was hidden to monitor their eye movements.

The LEDs were then each briefly illuminated at three different light intensities all in random order. The test was designed to be like a computer game and called the Star Catcher. If the LED flash occurred above, the child had to 'catch the star' by moving the joystick upwards, and if it occurred to the left they would have to move the joystick to that position. In this way, the team were able to verify that the child had seen the light and not just guessed, as has been the problem with previous visual field tests in children.

Dr Charlotte Codina, who undertook the study as part of her RNID-funded PhD said: "We found that deaf children see less peripherally than hearing children, but, typically, go on to develop better than normal peripheral vision by adulthood. Important vision changes are occurring as deaf children grow-up and one current theory is that they have not yet learnt to focus their attention on stimuli in the periphery until their vision matures at the age of 11 or 12.

"As research in this area continues, it will be interesting to identify factors which can help deaf children to make this visual improvement earlier."

RNID's Research Programme Manager, Dr Joanna Robinson, said: "This research shows that adults who have been deaf since birth may have advantages over hearing people in terms of their range of vision. For example, deaf people could be more proficient in jobs which depend on the ability to see a wide area of activities and respond quickly to situations, such as sports referees, teachers or CCTV operators.

"On the other hand, the findings suggest that parents of deaf children need to be aware that their child's initially delayed reaction to peripheral movements may mean they are slower to spot and avoid potential dangers such as approaching traffic."

(Photo: U. Sheffield)

University of Sheffield

EXTREME GLOBAL WARMING IN THE ANCIENT PAST

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Variations in atmosphere carbon dioxide around 40 million years ago were tightly coupled to changes in global temperature, according to new findings published in the journal Science. The study was led by scientists at Utrecht University, working with colleagues at the NIOZ Royal Netherlands Institute for Sea Research and the University of Southampton.

"Understanding the relationship between the Earth's climate and atmospheric carbon dioxide in the geological past can provide insight into the extent of future global warming expected to result from carbon dioxide emission caused by the activities of humans," said Dr Steven Bohaty of the University of Southampton's School of Ocean and Earth Science (SOES) based at the National Oceanography Centre in Southampton.

It has been known for some time that the long-term warmth of the Eocene (~56 to 34 million years ago) was associated with relatively high atmospheric carbon dioxide levels. However, scientists were previously unable to demonstrate tight-coupling between variations in atmospheric carbon dioxide and shorter-term changes in global climate.

To fill this gap in knowledge, the authors of the new study focused on one of the hottest episodes of Earth's climate history – the Middle Eocene Climatic Optimum (MECO), which occurred around 40 million years ago.

Algae use photosynthesis to harvest the energy of the sun, converting carbon dioxide and water into the organic molecules required for growth. Different isotopes of carbon are incorporated into these molecules depending on the environmental conditions under which algae grow. Ancient climate can therefore be reconstructed by analysing the carbon isotope ratios of molecules preserved in fossilised algae.

The researchers took this approach to reconstruct variations in carbon dioxide levels across the MECO warming event, using fossilised algae preserved in sediment cores extracted from the seafloor near Tasmania, Australia, by the Ocean Drilling Program. They refined their estimates of carbon dioxide levels using information on the past marine ecosystem derived from studying changes in the abundance of different groups of fossil plankton.

Their analyses indicate that MECO carbon dioxide levels must have at least doubled over a period of around 400,000 years. In conjunction with these findings, analyses using two independent molecular proxies for sea surface temperature show that the climate warmed by between 4 and 6 degrees Celsius over the same period.

"We found a close correspondence between carbon dioxide levels and sea surface temperature over the whole period, suggesting that increased amounts of carbon dioxide in the atmosphere played a major role in global warming during the MECO," said Bohaty.

The researchers consider it likely that elevated atmospheric carbon dioxide levels during the MECO resulted in increased global temperatures, rather than vice versa, arguing that the increase in carbon dioxide played the lead role.

"The change in carbon dioxide 40 million years ago was too large to have been the result of temperature change and associated feedbacks," said co-lead author Peter Bijl of Utrecht University. "Such a large change in carbon dioxide certainly provides a plausible explanation for the changes in Earth's temperature."

The researchers point out that the large increase in atmospheric carbon dioxide indicated by their analysis would have required a natural carbon source capable of injecting vast amounts of carbon into the atmosphere.

The rapid increase in atmospheric carbon dioxide levels around 40 million years ago approximately coincides with the rise of the Himalayas and may be related to the disappearance of an ocean between India and Asia as a result of plate tectonics – the large scale movements of the Earth's rocky shell (lithosphere). But, as explained by Professor Paul Pearson of Cardiff University in a perspective article accompanying the Science paper, the hunt is now on to discover the exact cause.

(Photo: John Beck, IODP)

National Oceanograpyh Center

NEW TIME LINE FOR APPEARANCES OF SKELETAL ANIMALS IN FOSSIL RECORD DEVELOPED BY UCSB RESEARCHERS

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Beginning around 542 million years ago, a profusion of animals with shells and skeletons began to appear in the fossil record. So many life forms appeared during this time that it is often referred to as the "Cambrian Explosion."

Geologists at UC Santa Barbara and a team of co-authors have proposed a rethinking of the timeline of these early animal appearances. Their findings are published in the latest issue of the Geological Society of America Bulletin.

Charles Darwin, in his book "On the Origin of Species," was troubled by the way the fossil record of this great proliferation of animals seemed to undermine his theory of evolution, and speculated that the pattern was due to the incompleteness of the geologic record.

"We found that with improved dating and correlation of rock sequences, the short burst of appearances goes away." said Susannah Porter, associate professor in the Department of Earth Science at UCSB. "Instead, appearances of the earliest skeleton-forming animals were drawn out over more than 20 million years."

UCSB graduate student John Moore added that skeletal animals became diverse much earlier than was thought, with nearly half of the animal genera in the dataset appearing in the first 10 million years of the Cambrian Period.

"The Cambrian diversification of animals was long thought to have begun with an explosive phase at the start of the Tommotian Stage, 17 million years above the base of the Cambrian," said Adam Maloof, first author and assistant professor of geosciences at Princeton University. "To test this idea, we matched earliest Cambrian records of carbon isotope variability from Siberia, Mongolia, and China with a Moroccan record constrained by five radiometric ages from interbedded volcanic ashes." This time interval was from 542-520 million years ago.

This approach avoids the circularity associated with using fossils to correlate rocks, and then using those correlations to infer biological patterns, explained Porter.

Porter said that, in addition to improving the timeline of early animal evolution, the team generated proxy records for sea level, carbon cycling, and the chemistry of oxidation-reduction in the ocean –– from the same sediments that contain the early animal fossils. The results indicate that early skeletal animals appeared during a 20-million-year interval of rising sea levels and increasingly oxidizing conditions at the sediment-water interface in shallow water environments.

(Photo: George Foulsham, Office of Public Affairs, UCSB)

UC Santa Barbara

PROFESSORS STUDY OLDEST FOSSIL SHRIMP PRESERVED WITH MUSCLES

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One of America’s favorite seafood is shrimp. Did you know that they fossilize as well? Rodney Feldmann, professor emeritus, and Carrie Schweitzer, associate professor, from Kent State University’s Department of Geology report on the oldest fossil shrimp known to date in the world. The creature in stone is as much as 360 million years old and was found in Oklahoma. Even the muscles of the fossil are preserved. Their study will be published in Journal of Crustacean Biology.

“The oldest known shrimp prior to this discovery came from Madagascar,” Feldmann said. “This one is way younger, having an age of ‘only’ 245 million years, making the shrimp from Oklahoma 125 million years older.”

The fossil shrimp, having a length of about 3 inches, was found by fellow paleontologist Royal Mapes of Ohio University and his students. Feldmann and Schweitzer named the fossil after him: Aciculopoda mapesi.

The discovery is also one of the two oldest decapods (‘ten footed’) to which shrimp, crabs and lobsters belong. The other decapod, Palaeopalaemon newberryi, is of similar age and was found in Ohio and Iowa. “The shrimp from Oklahoma might, thus, be the oldest decapod on earth,” Feldmann explained.

The fossil is a very important step in unraveling the evolution of decapods. However, more finds are necessary. “The common ancestor of the two species can probably be found in rocks that once formed the old continent Laurentia,” Schweitzer said. “Nowadays, these rocks can be found primarily in North America and Greenland. Who’s going to find it? Possibly by one of the numerous amateur collectors, who often graciously donate specimens to science.”

The description of the fossil is not only remarkable because of its age, but also due to its preservation. In this case, the muscles that once made up the tail part of the shrimp were preserved. This is extremely rare in fossils. Feldmann knows why the muscles are still visible. “When the animal died, it came to rest on the seafloor,” he said. “The muscles then were preserved by a combination of acidic waters and a low oxygen content as the animal was buried rapidly.”

The shrimp lived in deeper waters of the ocean where currents were too weak to destroy the shrimp. Other animals that were found in the same rock include the extinct ammonites, nautiloids, brachiopods and sponges.

(Photo: Rodney Feldmann/NOAA)

Kent State University

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