Monday, December 27, 2010

GEOLOGIST'S DISCOVERIES RESOLVE DEBATE ABOUT OXYGEN IN EARTH'S MANTLE

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While there continues to be considerable debate among geologists about the availability of oxygen in the Earth's mantle, recent discoveries by a University of Rhode Island scientist are bringing resolution to the question.

Analysis of erupted rock from Agrigan volcano in the western Pacific near Guam found it to be highly oxidized as a result of its exposure to oxygen when it formed in the Earth's mantle. When, over millions of years, seafloor rocks are transported back into the Earth's mantle at subduction zones – sites on the seafloor where tectonic plates have collided, forcing one plate beneath the other – they deliver more oxygen into the mantle.

The results of the research was presented at a meeting of the American Geophysical Union in San Francisco.

"The cycling of oxygen at the Earth's surface is central to the life and activity that takes place at the surface, but it is equally essential in the Earth's mantle," said URI Assistant Professor Katherine Kelley. "The availability of oxygen to the mantle is in part controlled by the oxygen at the surface."

Kelley said that this discovery is important because the availability of oxygen to the mantle controls what minerals are found there, how certain elements behave, and what kind of gasses might be expelled from volcanoes.

"The most primitive samples of lava we can identify are the most oxidized," she said. "That oxidation comes off the subducted plate at depth in the mantle and makes its way into volcanic magma sources that then erupt."

According to Kelley, some scientists have argued that the availability of oxygen to the mantle hasn't changed since the Earth was formed. However, if plate tectonics carry this oxidized material into the mantle, as she has demonstrated, then it is adding oxygen to the mantle. It also suggests that what takes place at the surface of the Earth probably influences what happens deep beneath the surface as well.

At Brookhaven National Laboratory, Kelley analyzed tiny olivine crystals that contain naturally formed glass from the early histories of magmas, in which are found dissolved gases from volcanic eruptions. By analyzing the glass she determined the oxidation state of iron in rocks and related it to the dissolved gases, which are elevated in subduction zone magmas.

This work follows a related study by Kelley that found that material from subduction zones are more oxidized than material from mid-ocean ridges where the plates are pulling apart. That study was published in the journal Science in 2009.

"These are important processes to understand, but they are hard to get a clear picture of because they take place over such long periods of time," Kelley said. "It's one piece of the big puzzle of Earth's evolution and how it continues to change."

The University of Rhode Island

FIGHTER PILOTS' BRAINS ARE 'MORE SENSITIVE'

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Cognitive tests and MRI scans have shown significant differences in the brains of fighter pilots when compared to a control group, according to a new study led by scientists from UCL.

The study, published in the Journal of Neuroscience, compares the cognitive performance of 11 front-line RAF (Royal Air Force) Tornado fighter pilots to a control group of a similar IQ with no previous experience of piloting aircraft. All the participants completed two 'cognitive control' tasks which were used to investigate rapid decision making. Diffusion tensor imaging (DTI), a type of MRI brain scan, was then used to examine the structure of white matter connections between brain regions associated with cognitive control.

The researchers found that fighter pilots have superior cognitive control, showing significantly greater accuracy on one of the cognitive tasks, despite being more sensitive to irrelevant, distracting information. The MRI scans revealed differences between pilots and controls in the microstructure of white matter in the right hemisphere of the brain.

Senior author Professor Masud Husain, UCL Institute of Neurology and UCL Institute of Cognitive Neuroscience, said: "We were interested in the pilots because they're often operating at the limits of human cognitive capability – they are an expert group making precision choices at high speed.

"Our findings show that optimal cognitive control may surprisingly be mediated by enhanced responses to both relevant and irrelevant stimuli, and that such control is accompanied by structural alterations in the brain. This has implications beyond simple distinctions between fighter pilots and the rest of us because it suggests expertise in certain aspects of cognition are associated with changes in the connections between brain areas. So, it's not just that the relevant areas of the brain are larger – but that the connections between key areas are different. Whether people are born with these differences or develop them is currently not known."

The study tasks were designed to assess the influence of distracting information and the ability to update a response plan in the presence of conflicting visual information. In the first task, participants had to press a right or left arrow key in response to the direction of an arrow on a screen in front of them, which was flanked by other distracting arrows pointing in different directions. In the second task, they had to respond as quickly as possible to a 'go' signal, unless they were instructed to change their plan before they had even made a response.

The results of the first task showed that the expert pilots were more accurate than age-matched volunteers, with no significant difference in reaction time – so, the pilots were able to perform the task at the same speed but with significantly higher accuracy. In the second task, there was no significant difference between the pilots and volunteers, which the authors say suggests that expertise in cognitive control may be highly specialised, highly particular to specific tasks and not simply associated with overall enhanced performance.

These findings suggest that in humans some types of expert cognitive control may be mediated by enhanced response gain to both relevant and irrelevant stimuli, and is accompanied by structural alterations in the white matter of the brain.

(Photo: UCL)

UCL

ROBOT ARM IMPROVES PERFORMANCE OF BRAIN-CONTROLLED DEVICE

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The performance of a brain-machine interface designed to help paralyzed subjects move objects with their thoughts is improved with the addition of a robotic arm providing sensory feedback, a new study from the University of Chicago finds.

Devices that translate brain activity into the movement of a computer cursor or an external robotic arm have already proven successful in humans. But in these early systems, vision was the only tool a subject could use to help control the motion.

Adding a robot arm that provided kinesthetic information about movement and position in space improved the performance of monkeys using a brain-machine interface in a study published today in The Journal of Neuroscience. Incorporating this sense may improve the design of "wearable robots" to help patients with spinal cord injuries, researchers said.

"A lot of patients that are motor-disabled might have partial sensory feedback," said Nicholas Hatsopoulos, PhD, Associate Professor and Chair of Computational Neuroscience at the University of Chicago. "That got us thinking that maybe we could use this natural form of feedback with wearable robots to provide that kind of feedback."

In the experiments, monkeys controlled a cursor without actively moving their arm via a device that translated activity in the primary motor cortex of their brain into cursor motion. While wearing a sleeve-like robotic exoskeleton that moved their arm in tandem with the cursor, the monkey's control of the cursor improved, hitting targets faster and via straighter paths than without the exoskeleton.

"We saw a 40 percent improvement in cursor control when the robotic exoskeleton passively moved the monkeys' arm," Hatsopoulos said. "This could be quite significant for daily activities being performed by a paralyzed patient that was equipped with such a system."

When a person moves their arm or hand, they use sensory feedback called proprioception to control that motion. For example, if one reaches out to grab a coffee mug, sensory neurons in the arm and hand send information back to the brain about where one's limbs are positioned and moving. Proprioception tells a person where their arm is positioned, even if their eyes are closed.

But in patients with conditions where sensory neurons die out, executing basic motor tasks such as buttoning a shirt or even walking becomes exceptionally difficult. Paraplegic subjects in the early clinical trials of brain-machine interfaces faced similar difficulty in attempting to move a computer cursor or robot arm using only visual cues. Those troubles helped researchers realize the importance of proprioception feedback, Hatsopoulos said.

"In the early days when we were doing this, we didn't even consider sensory feedback as an important component of the system," Hatsopoulos said. "We really thought it was just one-way: signals were coming from the brain, and then out to control the limb. It's only more recently that the community has really realized that there is this loop with feedback coming back."

Reflecting this loop, the researchers on the new study also observed changes in the brain activity recorded from the monkeys when sensory feedback was added to the set-up. With proprioception feedback, the information in the cell firing patterns of the primary motor cortex contained more information than in trials with only visual feedback, Hatsopoulos said, reflecting an improved signal-to-noise ratio.

The improvement seen from adding proprioception feedback may inform the next generation of brain-machine interface devices, Hatsopoulos said. Already, scientists are developing different types of "wearable robots" to augment a person's natural abilities. Combining a decoder of cortical activity with a robotic exoskeleton for the arm or hand can serve a dual purpose: allowing a paralyzed subject to move the limb, while also providing sensory feedback.

To benefit from this solution, a paralyzed patient must have retained some residual sensory information from the limbs despite the loss of motor function – a common occurrence, Hatsopoulos said, particularly in patients with ALS, locked-in syndrome, or incomplete spinal cord injury. For patients without both motor and sensory function, direct stimulation of sensory cortex may be able to simulate the sensation of limb movement. Further research in that direction is currently underway, Hatsopoulos said.

"I think all the components are there; there's nothing here that's holding us back conceptually," Hatsopoulos said. "I think using these wearable robots and controlling them with the brain is, in my opinion, probably the most promising approach to take in helping paralyzed individuals regain the ability to move."

The University of Chicago Medical Center

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