The limits of willpower. Every dieter knows that keeping the weight off is often harder than losing it. By performing fMRI scans on six obese individuals as they viewed photographs of food, both before and after they lost 10 percent of their body weight, Columbia University researchers have illuminated at least part of the reason. When the participants were shown the pictures after they'd lost the weight, sections of the brainstem involved in processing rewards were much more active than they had been in the pre-diet scans, presumably making that chocolate cake tougher to resist than in the past. Then the subjects got a shot of the appetite-dampening hormone leptin, which unhelpfully becomes less plentiful after dieting. Sure enough, with the artificial help the reward center returned to its pre-dieting calm, when logically it would be easier to push the cake away. "We're realizing that if you want to study obesity, you've got to look in the brain," says Hirsch, coauthor of the study. "It's clear there's so much more than willpower going on in a dieter struggling with overeating."
Gender's relationship to mood. Why do depression and anxiety disorders strike women more frequently than men? Two preliminary studies suggest key brain differences. When scientists at Children's Hospital of Philadelphia stressed both male and female rats by forcing them to swim, then examined slices of their brains using an electron microscope, they found the males had an ingenious stress-reduction response: They tucked some receptors for a stress-inducing hormone inside their brain cells. Female rats, by contrast, kept all the receptors exposed on the surface. In addition, the hormone bound more tightly to the receptors in the female brains. "The females were more sensitive to the stress neural hormone, and they didn't adapt as readily," says researcher Rita Valentino, director of stress neurobiology at the hospital. Similarly, when PET scans were performed on 46 men and women at the Karolinska Institutet in Stockholm, Sweden, the women turned out to have significantly more binding sites in certain parts of their brains for a chemical believed to be associated with depression.
The neuron-thought connection. Epilepsy patients sometimes need to have electrodes implanted inside their brains to reveal the sites of their seizures. An international team of scientists has taken advantage of this access to better understand the biology of memory. In a highly publicized 2005 study of volunteers with the electrodes, the team found that a specific neuron became activated when a patient viewed photographs of a well-known celebrity but not when he or she looked at photos of other stars or similar-looking women. Thanks to the discovery of what's been called the "Jennifer Aniston cell," scientists have realized that neurons are much more specialized than was previously believed, says coauthor Christof Koch, professor of biology and engineering at California Institute of Technology. The knowledge may one day lead to ways to identify and repair damaged neurons that impair certain memories.
How the mind focuses. Ever wonder how you can concentrate on a book in a noisy, crowded bus? Joy Hirsch's team has discovered the mechanisms that the brain apparently uses to stay focused in distracting situations. While monitoring the temporal lobe via fMRI, the researchers asked people to categorize, by profession, photographs of familiar actors or politicians as they flashed before them. In some cases, the labels on the pictures conflicted with the images; a photo of an actor might be marked with a politician's name. To help the brain focus on the images, extra blood rushed to the area believed to process faces. When the subjects were instructed to ignore the photos and instead categorize the profession based on the written name, the extra energy went to the "reading" center. Understanding how these processes "are engaged to either enhance or regulate behavior opens new doors for possibilities for treating many disorders of decision-making, including, perhaps, addictions," Hirsch says.
[Want to Be Happier? Keep Your Focus]