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Early Learning Periods Shape Brain's Capacity for Learning for Life
Sensitive periods of early learning can leave memory traces in the brain and thus influence an individual's ability to learn or perform later in life. This is according to a study reported in the March 6, 1998, issue of the journal Science.
The study, which was conducted using barn owls, shows that neuronal connections formed at an early age, while performing a specific task, can be reactivated in adulthood, even if those connections have remained unused for a long period of time. Neuronal connections are pathways that carry electrochemical impulses from one part of the brain to another. Owls that did not have the early learning experience were unable to perform the required task, presumably because they lacked or were unable to form the necessary neural connections.
"This study provides strong neurophysiological evidence to explain sensitive periods of learning. These sensitive periods have been identified in many species, including humans," noted James F. Battey, Jr., M.D., Ph.D., Director of the National Institute on Deafness and Other Communication Disorders, (NIDCD) one of the Institutes of the National Institutes of Health that provided partial support for this research.
The barn owl links its hearing and its vision to accurately locate and retrieve prey. Author Eric Knudsen, Ph.D., of the Stanford University School of Medicine, has been studying the neurological basis of this auditory and visual relationship which allows an owl to accurately locate and retrieve its prey, even in complete darkness.
In this study, prisms or special eyeglasses were attached to the young owl's head to shift the visual image that was sent to the brain slightly to the right. Dr. Knudsen then measured nerve cell activation of both auditory and visual neurons while the owl was listening to sounds that originated from various locations. At first, the activated auditory and visual neurons did not match and the owl would miss its target. However, over a period of six to eight weeks the activated visual neurons shifted to compensate for the prisms and again matched the auditory neurons. The owl would now be able to accurately retrieve its prey, even in the dark.
Once the shift in neurons was established the prisms were removed from the owls. Again, there was a mismatch between the activated auditory and visual neurons. Over another six to eight weeks, the visual and auditory neurons realigned.
"I proceeded to try the experiment on these same owls after they reached adulthood as well as on age-matched owls who did not have the prior experience," said Dr. Knudsen. The owls, which had previously worn the prisms as juveniles, retained their ability to shift the activated visual neurons to match the auditory neurons in the same 6 to 8 weeks. Owls that did not have the early experience could not shift the visual neurons to align with the auditory neurons, even after 12 weeks.
"This animal model, that has hearing, sound localization abilities and neural pathways known to be similar to those of humans, demonstrates a direct relationship between brain development and experience and that lack of experience at an appropriate time can render attainment of certain abilities difficult or incomplete," Knudsen concluded.
As the nation's focal point for research in human communication, the NIDCD conducts and supports biomedical and behavioral research and research training on normal mechanisms as well as diseases and disorders of hearing, balance, smell, taste, voice, speech and language that affect 46 million Americans.