An image believed to be that of a hole-punch cloud. Scientists say airplanes create these patterns when they fly through certain types of clouds. The water in the clouds can turn to rain or snow and fall to the ground. H. Raab/Vesta/Wikimedia Commons hide caption

itoggle caption H. Raab/Vesta/Wikimedia Commons

This image from April 27 shows a series of tornadoes forming over Alabama and Mississippi. Captured from a satellite orbiting located at a fixed location above Earth, images like these help track trends in weather patterns. Another set of polar-orbiting satellites are useful for long-term forecast predictions. NASA Earth Observatory hide caption

itoggle caption NASA Earth Observatory

This tornado touched down near Chickasha, Okla., on May 24. In addition to being tracked by the existing NEXRAD radar system, this storm was also being monitored by an experimental radar system that provided more precise information about the tornado's behavior and path. Heather Mosher/Courtesy National Weather Service/NOAA hide caption

itoggle caption Heather Mosher/Courtesy National Weather Service/NOAA

Scientists have known for a long time that nicotine decreases appetite among smokers, but they didn't know why. A new study finds that nicotine triggers a response in certain specific brain cells known to regulate appetite. hide caption

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An infant and his mother demonstrate electroencephalography, or EEG, technology at Children's Hospital Boston. The technology could help detect the risk of autism in infants. Courtesy of Michael Carroll hide caption

itoggle caption Courtesy of Michael Carroll

A study published in the journal Science last December suggested that a bacterium found in California's Mono Lake was able to substitute arsenic for phosphorous. But that conclusion has many critics. Miss Bliss 55 via Flickr hide caption

itoggle caption Miss Bliss 55 via Flickr

Amy Womack and her daughter, Alexis Nelson, sit on the front steps of her parents' house in Cleveland, Tenn., in late April. Womack says her father urged her and 13 relatives and friends into the basement before a tornado hit; she credits him with saving their lives. Wade Payne/AP hide caption

itoggle caption Wade Payne/AP

Residents of Joplin, Mo. salvage items from their home on Monday, a day after a devastating tornado struck the town. University of Oklahoma meteorologist Howie Bluestein says this could be be the last major tornado of the season, or "it could continue to be crazy." Charlie Riedel/AP hide caption

itoggle caption Charlie Riedel/AP

Learning juicy details about someone can change the way you see them — literally, according to a new study. August Darwell/Getty Images hide caption

itoggle caption August Darwell/Getty Images

1st Lt. Fred Simpson considers a computerized mental exercise designed to improve focus and memory. Simpson was knocked unconscious by a grenade blast in Afghanistan and now receives treatment at Walter Reed Army Medical Center in Washington. Maggie Starbard/NPR hide caption

itoggle caption Maggie Starbard/NPR

A patient participates in a brain-computer interface study. By placing an array of sensors directly on the brain and connecting them to a computer, researchers are able to decode brain signals into meaningful information, including some words. American Museum of Natural History Science Bulletins hide caption

itoggle caption American Museum of Natural History Science Bulletins

In a town in South Korea, one out of every 38 children tested had autism. Two thirds of these were undiagnosed and untreated, and seemed to be doing okay in school. Lee Jin-man/AP hide caption

itoggle caption Lee Jin-man/AP

Residents survey the destruction after a tornado hit Pratt City, Ala., on April 27. Short-term forecasting of twisters like the ones that swept the South this week has grown increasingly accurate, but long-term forecasting remains highly unreliable. Butch Dill/AP hide caption

itoggle caption Butch Dill/AP