"Instead of asking the owls to learn in one large step, we broke the problem down into small steps," said Brie Linkenhoker, a Stanford graduate student and first author on the paper. "We found that they could learn substantially more this way."
Adult animals are less able to learn new skills - witness any adult trying to master a new language. It turns out that the brains of younger animals are more able to make and break connections between neurons, allowing those animals to quickly pick up new skills and information. This phenomenon is the reason that children recover much faster from head injuries than adults.
To test adult learning, Eric Knudsen, PhD, the Edward C. and Amy H. Sewall Professor in the School of Medicine, and Linkenhoker took advantage of a quirk in barn owl brains. These owls develop a mental map of their world that aligns the auditory world with the visual one. When the animal hears a noise at a specific location, a nerve cell in the map region of the brain fires. That same nerve cell fires when the animal sees an object at that same physical location. The animals use this map with deadly accuracy to pinpoint prey when hunting at night.
In young barn owls, Knudsen has been able to alter the auditory map of the world by having the owls wear lenses that shift their visual world to the left or right. Over time, the young owl's brain compensates so that the auditory map once again coincides with the visual map. But pity the poor adult owl. When these owls wear world-shifting lenses, their brains adjust only slightly - about 9 percent of the shift seen in young owls. If the adult owl sees an object shifted 17 degrees to the right and hears a sound from that same physical location, two different regions of the brain fire.
Linkenhoker thought she could overcome this learning impairment by shifting the adult owl's vision in small increments. Rather than making a full 17-degree jump, five owls wore incrementally shifted lenses, going from 6 degrees, to 11 degrees, and finally to 17 degrees. Adult owls that received this graded training shifted their mental maps by 53 percent of the amount of adjustment seen in juvenile owls - the overlap between visual and hearing maps still wasn't perfect, but was much closer than in adult owls that tried to learn in one fell swoop. One owl adjusted so well to the 17-degree lenses that the researchers moved it to 23-degree lenses, to which it adjusted as well as the juvenile owls did.
The researchers say it makes sense that young owls could learn more quickly than adults. Their brains are adept at learning how to respond to the world around them while adult brains focus on retaining what they've already learned. "When your brain has lots of plasticity, it is not as reliable," Knudsen said. However, it is still a benefit for adults to slowly adapt as they age and their hearing changes. Knudsen added that adult owls near the top of the pecking order or living in stimulating environments have a much easier time adjusting to new conditions than less-social or bored owls.
Knudsen added that learning more about the conditions under which mature brains can adapt will be of help in treating brain injuries. After an injury, a child's brain recovers more quickly than an adult's. If Knudsen can work out ways to make an adult brain learn better, that information could help physical therapists treat adults more effectively after a stroke or injury. "A lot of therapy is done without insight into how the brain works," he said.
Stanford University Medical Center integrates research, medical education and patient care at its three institutions - Stanford University School of Medicine, Stanford Hospital & Clinics and Lucile Packard Children's Hospital at Stanford. For more information, please visit the Web site of the medical center's Office of Communication & Public Affairs at http://mednews.stanford.edu.
Journal
Nature