By trying to tickle(挠痒痒) rats and recording how their nerve cells respond, Shimpei Ishiyama and his adviser are discovering a mystery that has puzzled thinkers since Aristotle expected that humans, given their thin skin and unique ability to laugh, were the only ticklish animals.

    It turns out that Aristotle was wrong. In their study published on Thursday, Ishiyama and his adviser Michael Brecht found that rats squeaked and jumped with pleasure when tickled on their backs and bellies. These signs of joy changed according to their moods. And for the first time, they discovered a special group of nerve cells. These nerve cells made this feeling so powerful that it causes an individual being tickled to lose control.

    To make sure that he had indeed found a place in the brain where tickling was processed, Ishiyama then stimulated that area with electrical currents. The rats began to jump like rabbits and sing like birds.

    “It's truly ground-breaking,” said Jeffrey Burgdorf, a neuroscientist at Northwestern University who reviewed the paper. “It takes the study of emotion to a new level.”

    Burgdorf has played a central role in our understanding of animal tickling. He was part of a team that first noticed, in the late 1990s, that rats made special noises when they were experiencing social pleasure. Others had already noted that rats repeatedly made short and high sounds during meals. But the lab where Burgdorf worked noticed that they emitted similar sounds while playing. And so one day, the senior scientist in the lab said, “Let's go and tickle some rats.” They quickly found that those cries of pleasure doubled.

    “The authors have been very adventurous,” said Daniel O'Connor, a neuroscientist at Johns Hopkins University who studies touch. To him, that finding was very surprising.

    “Why does the world literally feel different when you are stressed out?” he said. “This is the first step towards answering that question. It gives us a way to approach it with experimental rigor(严谨).”

    You probably know who Marie Curie was, but you may not have heard of Rachel Carson. Of the outstanding ladies listed below, who do you think was the most important woman of the past 100 years?

    Jane Addams (1860-1935)

    Anyone who has ever been helped by a social worker has Jane Addams to thank. Addams helped the poor and worked for peace. She encouraged a sense of community by creating shelters and promoting education and services for people in need. In 1931, Addams became the first American woman to win the Nobel Peace Prize.

    Sandra Day O'Connor (1930-present)

    When Sandra Day O'Connor finished third in her class at Stanford Law School, in 1952, she could not find work at a law firm because she was a woman. She became an Arizona state senator(参议 员) and ,in 1981, the first woman to join the U. S. Supreme Court (最高法院). O'Connor gave the deciding vote in many important cases during her 24 years on the top court.

    Rosa Parks (1913-2005)

    On December 1,1955, in Montgomery, Alabama, Rosa Parks would not give up her seat on a bus to a white passenger. Her simple act landed Parks in prison. But it also set off the Montgomery bus boycott (联合抵制). It lasted for more than a year, and kicked off the civil-rights movement. "The only tired I was, was tired of giving in," said Parks.

    For many, music is as important to the human experience as eating and breathing. We hear music everywhere—at home, the gym, parties and stores. But what kind of music do we prefer to listen to, and when and why do our musical preferences change?

    The relationship between the change of seasons and musical preferences was the focus of a study led by psychologist Terry Pettijohn. He and his team based their research on a previous study that examined the relationship between popular music preferences and the Environmental Security Hypothesis(假设). The results showed that over time, when social and financial conditions were more risky, the songs of the year that were slower, longer, more comforting and serious were most popular. And during periods in which social and financial conditions were generally stable, the result was opposite.

    Building on these findings, Pettijohn and his team wondered if the Hypothesis could also be applied to the change of seasons. For college students, the participants in this study, autumn begins at the start of the school year. Gone are the carefree days of summer, when school is out. Winter means colder temperatures, shorter days, and, in many places in the country, snow. Spring, however, is a different story. It represents a fresh start and when clocks spring forward, we gain an extra hour of daylight. As students walk into summer, they're absorbed in the sunshine and social activities—and enjoy a break from school.

    But do changing seasonal conditions influence musical preferences? To answer this question, the researchers designed two studies. What did they find? Both groups of college students favored more serious music during the seasons of fall and winter, and more active and energetic music during the spring and summer seasons. And these findings, Pettijohn argues, have practical significances.

    It's a white Christmas in the United States today, with snow falling from Seattle to Maine.

    •Northeast

    Biting winds with snow swept the Northeast.

    Earlier, up to 15 inches of snow fell during a snow storm in Maine, while up to one foot fell in New Hampshire. Winds reached 76 mph on Cape Cod, Massachusetts, while up to 61 mph winds tore through Long Island, New York. Falling snow collected on the runways at Boston's Logan International Airport, causing temporary flight delays.

    The wind was so severe in Pennsylvania and New Jersey that the annual (重演) of George Washington and his soldiers' crossing the Delaware River was canceled, the Washington Crossing Historic Park told ABC News.

    •Midwest

    Heavy lake effect snow fell in western Michigan.

    The National Weather Service has issued a wind-chill warning and advisory (公告) from Montana to Michigan. Bitter cold air in the Midwest produced wind chills Monday morning as low as minus 48 degrees in North Dakota and minus 47 in northern Minnesota.

    As this bitter cold made its way east overnight, it was expected to move over relatively mild Great Lakes, producing intense lake-effect snow bands capabie of producing 2 to 4 inches of snow in an hour.

    •West Coast

    That storm system moved overnight through the Rockies, bringing more snow and the threat of avalanches (雪崩). The National Weather Service has issued an avalanche warning for the Wasatch Range Mountains outside Salt Lake City.

    Sweet potato plants don't have spines or poisons to defend themselves. But some have evolved a clever way to let hungry herbivores (食草动物) know they aren't an all-you-can-eat buffet, a new study finds. When one leaf injured, it produces a chemical that warms the rest of the plant and its neighbors to make themselves inedible (不宜食用的)to bugs. Sweet potato breeders could potentially engineer plants to produce the chemical as an all-natural pest defense.

    Plant ecologists led by Axel Mithofer of the Max Planck Institute for Chemical Ecology in Jena, Germany, started to look into sweet potato (Ipomoea batatas) defenses after they noticed something interesting about two varieties of the plant grown in Taiwan: The yellow-skinned, yellow-fleshed Tainong 57 is generally herbivore-resistant, but its darker orange cousin, Tainong 66, is plagued (造成麻烦) by insect pests.

    To find out why, the team offered up Tainong 57 and 66 plants to hungry African cotton leafworm caterpillars (毛虫).Both plants released at least 40 airborne compounds as the caterpillars snacked on their leaves. But Tainong 57 produced a lot more of a chemical called DMNT, which has a very distinct smell, the team details this month in Scientific Reports. ("The smell is not nice," Mithofer says. "You wouldn't want it as a perfume.")

    DMNT isn't a new compound; researchers have isolated (分离出) the smelly chemical from other plants such as corn and cabbage, and it is known to induce defense responses in some species.

    To determine whether this was happening in sweet potatoes, scientists set up two experiments. First, they put two plants next to each other and wounded one so it produced DMNT. Then, they exposed healthy Tainong 57 plants to DMNT they had synthesized (合成).In both cases, the DMNT caused the exposed plants to produce more of a protein called sporamin in their leaves. (Tainong 66 did not have the same reaction.) When the caterpillar's snack on sporamin, "they immediately stop eating because they don't feel well," Mithofer says.

    Sporamin is the main protein in sweet potato tubers (块茎),and is indigestible raw, which is why sweet potatoes must be cooked for humans to enjoy them. "If the caterpillars could cook it, they could eat it," Mithofer says. Theoretically, he says, sweet potato breeders could use genetic engineering to make different varieties of sweet potato produce as much DMNT as Tainong 57, and display the same defense responses.

    Still, the research isn't ready for prime time, cautions plant ecologist Martin Heil. DMNT might work in the lab, but in the field, airborne chemicals can be "blown away in seconds," says Heil, who studies plant-insect interactions at the National Polytechnic Institute in Irapuato, Mexico.

    Mithofer himself has no plans now to create genetically engineered sweet potato plants, because they would not be a viable (能活下去的) crop in Europe, where genetically modified crops are outlawed. So for now, Tainong 66 will have to put up with being a caterpillar salad bar.