September 19, 2002
National Geographic
Bijal P. Trivedi

The older we get, the tougher it is to pick up new skills like languages, music and mathematics. But a new study of juvenile and adult barn owls suggests that the older birds learn more, and faster, when their training goes step by step.

“We found that juvenile owls can pick up skills in leaps and bounds, whereas adults must take a series of baby steps,” says Eric Knudsen, a neurobiologist at the Stanford University School of Medicine, in California, who developed the research with his graduate student Brie Linkenhoker.

The barn owl, Tyto alba, study has lessons for human victims of brain injury who must relearn skills—and for general teaching practices as well. Knudsen and Linkenhoker’s research appears in the September 19 issue of Nature.

“There has never been so elegant a model demonstrating the differences in learning capabilities of the older and younger brain,” says Michael Merzenich, a neuroscientist at the University of California, San Francisco, whose laboratory studies the brain mechanics behind learning.

Nocturnal Hunters
Knudsen had used barn owls for earlier research on how the brain processes sound. “The barn owl is the best at sound localization,” he says.

For the new study, Knudsen and Linkenhoker compared how juvenile and adult barn owls adapted to a sudden change in their visual field.

Night-prowling barn owls have special low-light vision for hunting after sunset. In total darkness, the bird relies on its acute sense of hearing. Locating prey at night involves calculating a location by sound.

Based on information from its eyes and ears, the owl develops extremely sophisticated visual and auditory maps in its brain that enable it to zero in on the prey.

For their study, Knudsen and Linkenhoker changed the birds’ vision by delicately outfitting them with spectacles that shifted their visual field 23 degrees to the left or right.

The researchers hoped to investigate whether the owls’ brains would adapt—rewiring the neural circuitry over time—to align sounds with their new visual field.

Many Spectacles, Small Steps
Linkenhoker measured the responses of the bespectacled owls’ neurons in a region of the birds’ brain called the optic tectum, where visual and auditory maps merge. From this data she could determine whether the animals had adapted enough to map a sound to the correct location in their altered visual field.

Within two months of wearing the 23-degree prisms, young owls had fully adapted.

But even after four months of wearing the spectacles, the adults had only adapted about 10 percent as much as the juveniles.

Then Linkenhoker tried another approach. Instead of a one-step, 23-degree shift, Linkenhoker made a series of spectacles that incrementally shifted vision from 6 to 11 to 17 degrees.

With these gradual shifts the adults ramped up their learning curve and achieved slightly more than 50 percent of the juveniles’ adjustments.

One overachieving adult owl even made the jump from 17 to 23 degree lenses—fully adapting to the shifted visual field, just like the youngsters.

Adaptable vs. Reliable
“Knudsen has shown that adult owls are incapable of large reorganization of neural circuitry in their brains in response to a large change,” says Michael Stryker, a neuroscientist at the University of California, San Francisco. “But the study shows that the brain can be coaxed into great plasticity in adulthood with a specially designed training regimen.”

The life-stage change makes sense to Linkenhoker. “In the adult, the brain gives up plasticity to gain more reliability,” she says. “Whereas for juveniles it is important to adapt quickly, responding to the changing world around them.”

In humans, a stroke or an accident can cause the loss of certain skills like speech. But, with the right incremental training, victims may be able to relearn more than ever thought possible, researchers said.

“There’s something about successfully performing a task that allows us to build up skills—we reinforce what we know and then expand from this point,” Knudsen says.

The lesson from the bespectacled barn owls is that even old—or impaired—creatures can learn new tricks if they proceed by small degrees.