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Are you nuts for all things newfangled? Or do you stick with the tried and true? New research hints at how such personality traits may be wired into our brains.

Scientists have known for some time that the white matter in our brains--the strands of nerve fibers that connect nerve cell bodies, or gray matter--serve as the wires through which neural information flows. However, figuring out exactly which parts of the brain connect to each other, and how strong these connections are, has only been possible recently in living humans thanks to a technique called diffusion tensor imaging. A type of magnetic resonance imaging, the method traces the web of white matter by following the diffusion of fluid through the nerve fibers. Neurologists have used this technology in clinical studies to evaluate brain damage. Neurologist Bernd Weber of the University of Bonn in Germany, former Bonn psychologist Michael Cohen, and colleagues decided to take the tool in a new direction: "No one had really investigated [white matter's] connection to personality," says Weber.

To do this, the team asked a group of 20 volunteers to complete a survey to assess whether they were novelty seekers or comfort seekers. The volunteers answered true-or-false questions such as, "I like to try new things just for fun," or "I'd rather stay home than go out." The team then analyzed the volunteers' brains using diffusion tensor imaging, which revealed striking differences between the two groups: Novelty seekers sported a robust bundle of white matter linking the hippocampus, which forms memories and distinguishes between new and old experiences, to a region of the brain known as the ventral striatum, a major planning and reward center. In comfort seekers, on the other hand, the ventral striatum was more strongly connected to the frontal lobe, which plays a role in following social norms (among many other functions), the team reports online this week in Nature Neuroscience.

Other researchers are bullish on the work. "It's rare to find a structural correlation to such high cognitive behavior," says Tim Behrens, a psychologist at Oxford University in the U.K. "It's quite impressive." Turhan Canli, a psychologist with Stony Brook University in Stony Brook, New York, agrees. "There really aren't very many studies looking at the differences in white matter connectivity between individuals, ... which makes [the finding] quite valuable," Canli says. "When you look at the data, the association they see is quite striking."

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Graying matter. Elderly brains show less activity (red) than young brains in response to rewards.

Credit: Image courtesy of National Academy of Sciences, PNAS (© 2008)

Christmas morning: The kids throw on their clothes and wolf down breakfast so they can rip open their presents, while their grandparents loiter over their toast and coffee, seemingly more intent on finishing their meals than examining the holiday loot. It's not that Grandma and Grandpa hate Santa. Rather, new research shows, the same neurochemical that triggers excitement and rapid decision-making in the young just doesn't have the same effect for older folks.

Presents and other rewards cause a release of dopamine in the brain. Animal research has shown too little or too much dopamine can throw off activity in the prefrontal cortex (PFC), where most of our high-level decision-making takes place. Research in young adults suggests a similar relationship, but no one had examined dopamine's effect on PFC activity in the elderly.

To fill this gap, Karen Berman, clinical neuroscientist at the National Institute of Mental Health in Bethesda, Maryland, and colleagues turned to the two workhorses of human neuroscience research: positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). PET tracks how much of a particular chemical the brain produces; fMRI tracks moment-to-moment blood flow, pointing researchers toward areas of increased neural firing.

To examine the relationship between dopamine and the brain's response to rewards, the researchers recruited 20 individuals averaging 25 years of age and 13 individuals averaging 66 years of age. While inside an fMRI scanner, the subjects viewed a series of 16 slot machine games on a computer screen. The slot machine first showed the chance of winning a set amount of money. After a 15-second delay, the screen showed how much money the subjects actually received. The researchers repeated the test, this time using PET to measure overall dopamine production during the testing period.

Increased dopamine production in young people was linked to more brain activity in the prefrontal cortex, as measured by the fMRI. But the elderly showed the opposite relationship, meaning older subjects who made more dopamine actually had less activity in their prefrontal cortex, the researchers report online today in the Proceedings of the National Academy of Sciences. "So you're getting less bang for your [dopamine] buck," Berman says. Across the board, the elderly subjects also showed less activity in the brain areas that control arousal, suggesting they were less excited at the thought of the reward.

Amy Arnsten, a neuroscientist at Yale University who first described the relationship between dopamine and PFC activity in animals, says the work offers good and bad news. Although Grandpa may not need a top-notch PFC to coordinate his gift-unwrapping sessions, the elderly do need a PFC in good order to make major decisions such as deciding on health insurance or investing life savings. In those situations, an impaired dopamine reward system could cause major problems. "To have those functions impaired [in the elderly] when you may be needing them most is really rotten." But research like this could eventually lead to effective treatments to stabilize impaired dopamine systems in the elderly, Arnsten says.

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Four-winged wonder.
A couple of extra wings help dragonflies accomplish amazing things.

Credit: Jupiter Images

The dragonfly is an aerial acrobat. It's able to fly fast and slow, backward and forward, and even stay aloft while copulating. Where does the energy for all of these stunts come from? A new report in today's issue of the Journal of the Royal Society Interface suggests that the answer has to do with the insect's four independently moving wings.

Most flying insects use only a single pair of wings. Some, like butterflies and bees, use two pairs but synchronize their motion so that the effect is akin to having just two wings. Dragonflies and damselflies stand apart: Unusual musculature allows them to move each of their four wings independently. Computer modeling has shown that such out-of-phase flapping comes at a cost, however, reducing the amount of lift the insect is able to generate.

To see if these computer models hold up in the tangible world, James Usherwood, a biologist at the Royal Veterinary College in London, and Fritz-Olaf Lehmann, a biologist at the University of Ulm in Germany, built a robotic version of a dragonfly. They immersed the robot in mineral oil seeded with air bubbles to allow them to visualize the movement of the fluid around the flapping wings. Sensors at the base of the robot's wings recorded lift and drag forces, which allowed the team to calculate its aerodynamic efficiency.

Flapping four wings actually achieved lift with more efficiency than flapping just two wings. When the robot's hind wings flapped one-quarter of a wing beat ahead of the front wings, the team reports, the hind wings were able to capture the rush of air sent by the front wings and produce lift with 22% less power than two-winged insects require. Flapping in phase has benefits, too: When real dragonflies synchronize their wing beats, they are able to lift off and accelerate better than if they used only two wings or four out-of-sync wings, the authors say. Engineers may be able to apply these findings to building the next generation of flapping micro air vehicles, says Lehmann.

Jane Wang, a mathematician at Cornell University, says that the data agree with her own computer models of hovering dragonflies and that the new study elucidates why out-of-phase flapping is so efficient. Richard Bomphrey, a biologist at the University of Oxford in the U.K., cautions that scientists need to validate the findings in living insects. Still, he agrees that the research could ultimately aid engineers. The main difficulty facing the designers of micro air vehicles is that battery life limits how long the devices stay aloft, he says, so "any tips or tricks which enhance aerodynamic efficiency will be warmly welcomed."

Related site

• More about micro air vehicles
• More about dragonflies

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Fighting brain?
A youngster with a larger-than-average amygdala (right) may have more tantrums than one with a smaller version (left).

Credit: Sarah Whittle and study group

Teens who are more likely to argue aggressively and persistently with their parents also have brain structures of different sizes, a new study finds. On average, a sassy kid has a larger amygdala, the part of the brain that processes emotional responses, than a cooperative one. The findings could help scientists understand the roots of aggressive behavior in teens.

For teenagers, the battle begins within. When hormones surge in puberty, the amygdala grows in size and becomes more active, leading to rash and emotional behavior. Like a chaperone, the prefrontal cortex regulates the amygdala to ensure socially correct behavior. But during adolescence, it still has maturing to do, scientists speculate, so the amygdala is left poorly supervised. As a person grows into adulthood, inhibitory connections between these two regions increase and the prefrontal cortex catches up with the amygdala. This structural change--the growth of the prefrontal cortex and shrinking of the amygdala--could account for less impulsive behavior in adulthood.

Nicholas Allen, a psychologist at the University of Melbourne, Australia, wanted to find out whether brain structure influences a teenager's day-to-day emotional state. He and colleagues from the Orygen Research Centre in Melbourne and the Oregon Research Institute in Eugene videotaped 137 preteens and teenagers between the ages of 11 and 14 as they talked with their parents about issues that often lead to disagreements--such as bedtime, homework, or cell-phone use. The researchers scored the conversations based on their content and other factors such as facial expressions and tone. They also used brain imaging to measure the volume of different brain structures among the youths. Those with a larger amygdala, relative to the total brain size, showed more aggressive behavior while talking with their parents in these sessions.

In addition, boys with a left prefrontal cortex larger than the right were less emotionally reactive, the researchers report online this week in the Proceedings of the National Academy of Sciences. Allen speculates that the left side of the cortex plays a greater role in squelching impulsive behavior, meaning that when it's larger than the right side, impulses may be better controlled.

The study doesn't show that a larger amygdala causes the behavior differences, but it's a good start toward spelling out the connection, says psychiatrist Jay Giedd of the National Institute of Mental Health in Bethesda, Maryland. Researchers have been seeking a connection "between the brain imaging and the 'so what,' or the clinical significance," he says, but that link "has been elusive." The next step is to track these adolescents and see how their brains change over time, Giedd says: "It is the right approach; there is more to come."

Related site

• National Institute of Mental Health on the Teenage Brain