March 11, 2011 6:16 pm

How the brain retrains itself

 
Two blind girls having fun

In those born blind, parts of the visual cortex are recruited for language processing

Neuroscientists are beginning to appreciate the remarkable adaptability of the human brain. This “plasticity”, to use the technical term, means that one specialised brain area can take over some functions normally performed by another area, if circumstances such as disability or injury make the change desirable.

Early evidence that the division of labour in the brain was not as clear-cut as neuroscientists once believed came from a 1996 study of blind people, which showed that the visual cortex could participate in a non-visual function: reading Braille.

Now, research at the Massachusetts Institute of Technology (MIT) has shown that in people who are born blind, parts of the visual cortex – normally used to process input from the eyes – are recruited for language processing. The finding suggests that the visual cortex can change its function radically, and it overturns the idea that language processing can only occur in specialised brain regions.

“Your brain … doesn’t develop along a fixed trajectory, rather it’s a self-building tool kit,” says Marina Bedny, lead author of the study, which appears in the Proceedings of the National Academy of Sciences.

For more than a century, neuroscientists have known that two specialised brain regions – Broca’s area and Wernicke’s area – are necessary to produce and understand language, respectively. They were thought to have intrinsic properties, such as an internal arrangement of cells and connectivity with other brain regions, which make them uniquely suited to process language.

To investigate, the MIT researchers scanned with fMRI the brains of congenitally blind volunteers as they undertook oral sentence comprehension tasks. The visual cortex was very active, in addition to the classical language areas, while the subjects wrestled with grammatical structures and word meanings. In sighted controls, only the classical Broca’s and Wernicke’s areas were involved.

The study does not refute the idea that the human brain needs Broca’s and Wernicke’s areas for language. “We haven’t shown that every possible part of language can be supported by [the visual cortex]. It just suggests that a part of the brain can participate in language processing without having evolved to do so,” Bedny says.

Why should the visual cortex take part in language processing, when the Broca’s and Wernicke’s areas are already functioning normally? Probably because the brain develops to make maximum use of all resources.

The next step will be to investigate whether this redistribution gives blind people an advantage in language processing – whether they perform better than sighted people in complex language tasks while being distracted.

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Chilling truth about Antarctic ice

When water freezes, we expect ice to start forming on the surface then thicken from the top downwards. But an expedition to the heart of Antarctica has found that the opposite process takes place deep under the continent’s ice sheet.

Lakes of liquid water, which exist beneath 2km-4km of ice across much of Antarctica, regularly freeze from the bottom upwards, according to a study published in the journal Science.

The researchers used radar to discover what was going on around the Gamburtsev subglacial mountains, beneath the highest part of the ice sheet known as Dome A.

They found that “freeze-on” ice, which originated from the bottom rather than the top, makes up 24 per cent of the sheet there – and in some places accounts for as much as half.

“We usually think of ice sheets like cakes – one layer at a time added from the top [through the build-up of snowfall]. This is like someone injected a layer of frosting at the bottom – a really thick layer,” says Robin Bell, a geophysicist at Columbia University.

Deeply buried Antarctic ice melts through heat created by friction as the ice moves at a glacial pace over the bedrock and because geothermal energy is radiated from within the Earth. Once melted it can remain liquid at temperatures well below the normal freezing point of water, because of the high pressure exerted by all the ice above.

Refreezing from the bottom takes place when the ice gets squeezed up against the mountains, because of changing pressure and the penetration of lower temperatures from the surface.

“Understanding these interactions is critical for [understanding] subglacial environments and ice sheet dynamics,” says Fausto Ferraccioli of the British Antarctic Survey. “Incorporating these processes into models will enable more accurate predictions of ice sheet response to global warming and its impact on future sea-level rise.”

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Java ‘mud volcano’ to continue flowing

The people of Sidoarjo on the island of Java, Indonesia, may have to endure a mud volcano for the next 26 years, according to researchers from Durham University, writes Jack Serle

The Lusi volcano erupted on May 29 2006 killing 13 people and displacing 13,000 families – and is still active today. It was at one point the fastest-growing mud volcano recorded. Now covering an area of 7sq km, the volcano engulfed homes and factories as it grew.

Although the initial period of eruption was catastrophic, Lusi’s rate of expansion has slowed. While mud flows no longer pose a risk to the local population, there are secondary effects which carry their own danger. According to Richard Davies, lead author of a paper in the Journal of the Geological Society, “116 other vents have appeared in factories, houses and roads in the surrounding area.”

These vents are caused by subsiding land which has opened fissures in an aquifer, releasing more pressurised water. This rising water can carry natural gas with it, bringing a risk of explosion.

What triggered the eruption has been closely debated. In 2007 British scientists suggested drilling for gas deposits was the cause. The drilling company contested this, putting the blame on an earthquake 280km away.

Whatever the trigger, drilling has contributed to the eruption.

A vertical well, from the gas prospecting, links an area of highly pressurised water to a stratum of mudstone. This column, Davies believes, eased the ascent of heated water and mud that erupted five years ago.

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Bush plants harmed by controlled burning

A standard way to reduce the danger of bushfires is by controlled burning of limited areas. But this practice of “prescribed burning” does more harm than good in some environments, according to leading British and Australian botanists.

They argue that deliberately increasing the frequency of fires, to reduce the amount of inflammable vegetation, may lead to ecosystem degradation and loss of biodiversity.

In a paper in the journal Trends in Plant Science the scientists say there is little evidence that Mediterranean-climate plants are adapted to fire, as land managers sometimes claim.

Stephen Hopper, director of the Royal Botanic Gardens, Kew, who is from Western Australia, says: “Our analysis reveals that it is naive on present evidence to assume that Australian plants are adapted to fire, and that prescribed burning regimes are not only good for the bush but can be applied in any fashion and frequency with impunity.”

The authors argue that the role of fire in the evolution of Mediterranean plants has never been proved. Traits traditionally regarded as evidence of adaptation to fire, including smoke-induced germination, also occur in ecosystems that are not fire-prone and stimulate germination in plants such as lettuce and tomatoes.

“Preventing an increase in fire frequency – instead of prescribed burning – can be crucial for maintaining soil integrity, water supplies, water quality and biodiversity,” the authors write.

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