"Things that an animal learns during an early period of life can alter the brain's anatomy dramatically," said Eric Knudsen, PhD, the Edward C. and Amy H. Sewall Professor of Neurobiology at Stanford University Medical Center. Knudsen will present findings Saturday about how early experiences mold the brain of barn owls during a talk titled "The Effects of Early Experience on Brain and Brain Development," at the annual meeting of the American Association for the Advancement of Science in Denver.
Knudsen's work takes advantage of the barn owl's keen sense of hearing. 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 location. The animals use this map with deadly accuracy to pinpoint the scratching and squeaking of mice 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. When Knudsen removes the glasses, these owls return to their original mental map of the world.
Owls that had this early learning experience are forever different from their contemporaries, Knudsen reported in a 1998 Science paper. As adults, when Knudsen puts world-shifting lenses on the owls, only those that had early experience with the lenses can adjust. "Changes in the brain that are induced by early experience result in a persistent effect that can be reused later in life," he said. Owls that lacked the early experience could not form a new mental map.
In a 1999 Science paper, Knudsen reported not on how owls learn, but how they forget - and the lasting changes within the brains of owls that had once known a different special map. These owls actively suppressed the normal map while they were wearing lenses.
"For an owl to be able to localize the sound correctly after wearing the prisms it has to be able to forget the older map, which is not behaviorally appropriate, and follow the new map," said Weimin Zheng, PhD, a postdoctoral fellow in Knudsen's lab at the time. Forgetting the older map involves a specific set of inhibitory neurons that suppress the map but don't erase it. Knudsen said that for experiences learned early in life some portion of the circuitry remained intact, waiting to be needed in the adult animal.
All is not lost for those older folks whose brains resist learning new tricks. According to a paper in the Sept. 19, 2002, issue of Nature, older brains can still learn, but only if change comes slowly. Knudsen reported that when the vision of adult owls was shifted in small increments rather than in one fell swoop they were able to adjust to their altered view of the world. Adult brains may not have the plasticity of younger brains, Knudsen said, but they can still learn when called upon to do so.
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