The world's deepest-dwelling centipede — found as much as 3,600 feet below the surface — is in Croatia, a study in ZooKeys reports. The centipede was found in three caves in the Velebit mountain range, along the Adriatic Coast. It has powerful jaws with poison glands and long, curved claws that allow it to clutch its prey. And like other cave-dwelling arthropods, it has elongated antennas, trunk segments and leg claws. Researchers named the centipede Geophilus hadesi, after Hades, the Greek god of the underworld.

Tracing how we make memories

Learning can be traced back to individual neurons in the brain, a study said.

"What we wanted to do was see if we could actually create a new association — a memory — and see if we would be able to see actual change in the neurons," said Matias Ison, a neuroscientist at the University of Leicester in England and an author of the study in journal Neuron.

He and his colleagues were able to monitor the brain activity of neurosurgical patients at UCLA Medical Center. The patients were first presented with images of notable people — such as Jennifer Aniston, Clint Eastwood and Halle Berry.

Then, they were shown images of the same people against different backdrops — such as the Eiffel Tower, the Leaning Tower of Pisa and the Sydney Opera House.

The same neurons that fired for the images of each of the actors also fired when patients were shown the associated landmark images. In other words, the researchers were able to watch as the patients' neurons recorded a new memory. The research could help scientists better understand how the brain encodes and stores new memories, Ison said.

U.S. warns of risk to polar bears

Polar bears are at risk of dying off if humans don't reverse the trend of global warming, a blunt U.S. government report said.

"The single most important step for polar bear conservation is decisive action to address Arctic warming," the U.S. Fish and Wildlife Service said in a draft recovery plan, part of the process after the agency listed the species as threatened in 2008.

"Short of action that effectively addresses the primary cause of diminishing sea ice, it is unlikely that polar bears will be recovered."

Halting Arctic warming will require a global commitment, said Jenifer Kohout, the Fish and Wildlife Service's regional program manager and a co-chair of the polar bear recovery team.

Greenhouse gas emissions contribute to global warming, which is reducing the amount of summer sea ice in the Arctic. Polar bears use sea ice for feeding, mating and giving birth. The Office of Naval Research said the past eight years have had the eight lowest amounts of summer sea ice on record.

At an Arctic Council meeting in Canada this spring, the United States, Russia and other Arctic countries vowed to cooperate on combating climate change.

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