Chris Stephens, 28, who has been battling depression all of his life, plays with his dogs at home in Concord, Calif., on Friday. After a dose of ketamine, Stephens says, "I actually wanted to do things. I wanted to live life." Lianne Milton for NPR hide caption

itoggle caption Lianne Milton for NPR

Ketamine has been used as an anesthetic for decades. It's also a widely popular but illegal club drug known as "Special K." When administered in low doses, patients report a rapid reduction in depression symptoms. Huw Golledge/flickr hide caption

itoggle caption Huw Golledge/flickr

Even in the remote Faroe Islands, some children have high levels of perfluorinated compounds in their blood. The chemicals may interfere with the immune system. Stig Nygaard/Flickr hide caption

itoggle caption Stig Nygaard/Flickr

Researchers claimed in late 2010 that they found bacteria in Mono Lake, Calif., that survived on the poison arsenic in the place of an element thought essential to life. The report was immediately greeted with skepticism from the scientific community. Ben Margot/AP hide caption

itoggle caption Ben Margot/AP

A tufted capuchin uses a stone hammer to crack open a nut in Brazil's Parnaiba Headwaters National Park. Ben Cranke/Getty Images hide caption

itoggle caption Ben Cranke/Getty Images

A Harvard study found dramatically higher BPA exposure in people who ate canned soup. The researchers used different varieties of Progresso-brand vegetable soups, but BPA is found in the epoxy resins used to coat the inside of many food and beverage cans. Maggie Starbard/NPR hide caption

itoggle caption Maggie Starbard/NPR

The most common cause of brain injury in premature infants is a lack of oxygen in the days and weeks after birth, researchers say. Ibrahim Usta/AP hide caption

itoggle caption Ibrahim Usta/AP

A healthy gypsy moth caterpillar on a leaf. Outbreaks of gypsy moths damage roughly 1 million acres of forest in the U.S. each year. Michael Grove/Science/AAAS hide caption

itoggle caption Michael Grove/Science/AAAS

The brain "seems to be specialized in alerting us to things that are emotionally important to us — either positive or because they're scary," a scientist says. iStockphoto.com hide caption

itoggle caption iStockphoto.com