14 | NewScientist | 1 February 2014

THIS WEEK

THE most influential brain in neuroscience has been reconstructed in 3D, which should give us insights into memory for years to come.

Henry Molaison from Connecticut had several areas of his brain removed to treat his epilepsy in 1953. After the surgery, Molaison – known as patient H.M. until his death in 2008 – could not form new memories, a condition known as anterograde amnesia. He also had difficulty recollecting his long-term past.

Molaison’s willingness to allow people to study what he could remember allowed researchers to understand how the brain areas that were excised are involved in memory. He died of respiratory failure in 2008 and bequeathed his brain to science. Now Jacopo Annese at the Brain Observatory in San Diego, California, and his colleagues have dissected it and conclusively linked Molaison’s memory problems to damaged areas. They have also constructed a virtual 3D model of his brain (Nature Communications, DOI: 10.1038/ncomms4122).

At the time of Molaison’s surgery, many researchers believed that memory was stored throughout the brain. After the surgeon removed portions of Molaison’s temporal lobes, which included an area called the hippocampus on both sides of his brain, Molaison never again remembered an event, or a

conversation he’d had only moments before. But he was still able to learn new skills – albeit without remembering that he had been practising them. This showed that such “procedural memory” must be located outside the removed areas.

Later scans provided more detail about what had been excised, but they were not of high-enough resolution to reveal the exact anatomical boundaries. Only dissection could reveal the full extent of the surgery.

Annese and his colleagues froze Molaison’s brain, then cut it into

2401 slices, 70 micrometres thick, taking pictures of every slice. Each one was separately preserved.

They created a detailed 3D digital model from the images. Now doctors will be able to revisit – by virtual dissection – Molaison’s surgery, and find out exactly what was removed.

The detailed brain map shows that Molaison retained a large portion of his hippocampus in both hemispheres. However, the removal of his entorhinal cortex, which acts as a gateway for information to and from the hippocampi, is likely to have hampered full functioning.

Molaison lacked the ability to report internal states – he could not feel pain, or tell if he was hungry or thirsty. His dissection revealed why – his amygdalae, now known to regulate emotions and internal states, were almost completely removed.

“We knew the cause of the damage. What we didn’t have until now was precise knowledge of which anatomical areas were involved,” says Malcolm Macmillan at the University of Melbourne in Australia.

Molaison is probably the most studied person in neuroscience, says Annese. “This collection of slices and digital images will provide an unprecedented opportunity for his contribution to neuroscience to continue far beyond his death,” he says. n

Helen Thomson

–Slice of history–

Most famous brain gives a parting gift

Cyclone action in Australia hits 1500-year lowOFF the chart: cyclone activity in Australia has been lower over the last 40 years than at any time in the past 1500 years. The seemingly good news comes with a sting in the tail for people living on the coast.

Radar and satellite records of tropical cyclones – rotating storm systems – stretch back only about four decades. For an idea of trends

on the longer term, researchers must go underground.

Compared with typical monsoonal rains, the severe rains associated with tropical cyclones are unusually low in the heavier oxygen isotope – oxygen-18. Stalagmites forming in caves record this difference, so by analysing their growth bands – which form each year in the wet season – geologists can establish whether or not a given year was characterised by cyclone activity.

Jordahna Haig and Jonathan Nott of James Cook University in Cairns, Queensland, Australia, and their

colleagues examined stalagmites from the coast of Queensland and Western Australia. Their results show that cyclone activity in Australia since 1900 is dramatically lower than at any time since about AD 500. There was an even steeper drop from about 1960, corresponding closely with the sharp increase in global temperatures (Nature, DOI: 10.1038/nature12882).

Climate models predict that

cyclone frequency will decrease – and individual cyclones will become more intense – as the world warms. However, these effects were only expected to be significant by about 2050. “What we’re saying is that we’re seeing this now,” says Nott.

That’s bad news for people living on Australia’s coast, because it suggests that the infrequent cyclones they experience will be more intense, with stronger storm surges and more flooding than past cyclones. “We’ve grossly underestimated the risks with building close to sea level,” says Nott. Michael Slezak n

“The seemingly good news comes with a sting in the tail for people living on the coast”

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