19 October 2013 | NewScientist | 17

Brain cells that only love numbers

A PART of all of us loves sums. Eavesdropping on the brain while people go about their daily activity has revealed the first brain cells specialised for numbers.

Josef Parvizi and his colleagues at Stanford University in California enlisted the help of three people with epilepsy whose therapy involved placing a grid of electrodes on the surface of their brain that record activity.

Neurons fired in a region called the intraparietal sulcus when the three volunteers performed arithmetic tests, suggesting they dealt with numbers.

The team continued to monitor brain activity while the volunteers went about their normal activity in hospital. Video footage of their stay revealed that the neurons remained virtually silent for most of the time, bursting into life only when the volunteers talked about numbers or numerical concepts such as “more than” or “less than” (Nature Communications, DOI: 10.1038/ncomms3528).

There is debate over whether some neural populations perform many functions or are involved in very precise tasks. “We show here that there is specialisation for numeracy,” says Parvizi.

Hunter-gatherers clung on after invasion of first farmersEUROPE’S first farmers and its last hunter-gatherers probably lived side by side for millennia.

Farming spread to Europe from the Middle East around 7500 years ago, and continued to expand westwards – apparently because the incoming farmers outcompeted the native hunter-gatherers. Now an analysis of ancient people’s diets offers a more harmonious scenario.

Ruth Bollongino of Johannes Gutenberg University in Mainz, Germany, and colleagues looked at the isotope content of 25 bodies

found at a burial site in Blätterhöhle cave in Germany. The analysis showed that the people living between 10,300 and 11,200 years ago, before farming spread to Europe, mostly ate a typical hunter-gatherer diet of wild animals. But the people who lived between 6000 and 5000 years ago could be divided into two populations with different diets.

One of these populations ate mostly domestic animals, suggesting they were farming. But the other, living alongside them, mostly ate freshwater fish, typical

IS THE earthworm turning into a global warming saviour? Earlier this year, the animals were cast as key contributors to climate change, but they may have been falsely accused.

A fifth of carbon dioxide emissions come from soils, and earthworms play a central role. They churn up soil, encouraging breakdown of organic matter to produce CO2. They also drive subterranean processes that both lock up and release carbon.

A recent review of more than 200 published studies concluded that worms increase CO2 emissions from soils by a third on average.

Weixin Zhang of the South China Botanical Garden in Guangzhou says things are more complex. His team’s work shows that microbes in the guts of earthworms convert organic carbon into a form that can be stored in soils (Nature Communications, DOI: 10.1038/ncomms3576).

“We believe the recent estimation of earthworms increasing soil emissions by 33 per cent is likely a severe overestimate,” says Zhang. The findings could be important in future assessments of climate change, especially as earthworms spread to higher latitudes.

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of hunter-gatherers, indicating that the lifestyle persisted in the area until 5000 years ago, perhaps 2000 years after farmers arrived.

The migrant farmers and local hunter-gatherers must have lived as neighbours for many years, says Bollongino. “We are pretty sure they were in contact.” They shared the burial site, and may have traded and interbred. Over time, farming populations probably grew much bigger than those of hunter-gatherers because of the sheer quantity of food produced (Science, doi.org/n82).

Titanic diamonds drift inside Saturn

GIANT “diamondbergs” could be floating inside Jupiter and Saturn. This sparkling picture is based on an analysis that suggests the planets have the right conditions for crushing carbon into diamond.

Mona Delitsky of California Specialty Engineering in Pasadena and her colleagues combined new atmospheric models with updated knowledge of carbon’s behaviour under extreme conditions.

Their work, presented last week at an astronomy meeting in Colorado, showed that lightning storms on Saturn can split methane in the upper atmosphere, producing carbon soot. As the soot falls into the planet’s interior, pressure and temperature increase, crushing it into diamonds that can grow to cinematic sizes. Conditions to host diamonds also exist on Jupiter, they say, although a mechanism to create them remains unclear.

Just because diamonds can exist doesn’t mean they do, says Luca Ghiringhelli of the Fritz Haber Institute of the Max Planck Society in Berlin, Germany. He thinks it is not clear that a diamond nucleus could form inside these planets to seed the growth of a larger stone.

But if Delitsky’s team is correct, all the solar system’s gas giants might be littered with bling. Earlier research suggested that Uranus and Neptune also have the gems.

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