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Scientists Teach Old Owl New Tricks
Daily Excelsior, 21 September 2004
http://www.dailyexcelsior.com/02sep22/inter.htm

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PALO ALTO, CALIFORNIA: Neuroscientists have taught an old owl new tricks with a strategy that also may work to restore some of the youthful pliability to aging human brains too set in their ways to adapt easily to change.

The experiments looked at neurological re-adjustments made by owls wearing prism glasses, which distorted their view of the world. The findings could have implications for treating brain disorders and injuries, rehabilitating stroke victims who have difficulty relearning motion and speech and even acquiring a new language in adulthood, researchers told United Press International (UNI).

In many species, grown ups lose the childhood facility of dealing with change. However, the new research, detailed in the September 19 issue of the British journal nature, suggests as long as the shift is incremental, the mature brain can be made more malleable, although not to the levels characteristic of the early developmental stage.

The brains of the young ó with their sponge-like ability to absorb new information and skills ó have greater capability than do those of the old to make and break connections between critical nerve cells called neurons.

The young are adept at acquiring entirely new kinds of information in large chunks. Not so adults, who have much more severe constraints imposed by the nervous system, lead study author Eric Knudsen, the Edward C. And Amy H. Sewall Professor at Stanford University School of Medicine, said in an interview on Wednesday.

Thus, a child recovers from a head injury or picks up a new language faster than does an adult, investigators told UNI.

Age reduces the brainís ability to adapt to change. But a surprising measure of neural adaptation does occur, at least in one experimental situation, if change is introduced bit by bit, said Hemai Parthasarathy, senior editor at nature who analysed the findings in a commentary. This study is a very interesting demonstration of unexpected plasticity in a system we thought was pretty much set in stone, she told UNI.

They say that you canít teach an old dog new tricks. But .. (first author Brie) Linkenhoker and Knudsen provide evidence that you can at least teach an old owl new tricks ó if you train it in small steps. This result implies that the brains of older animals, including ourselves, may be capable of greater change in the form of adaptive plasticity than previously expected.

The scientists developed a step-by-step training programme that allowed adult owls to adjust to prism glasses that placed what they saw at odds with what they heard. The glasses made objects appear to the right or left of where they actually were situated. If the changes were incremental ó with successive lenses skewing the picture a bit at a time, rather than dramatically altering it all at once ó the owlís brain realigned the auditory input to mesh with the visual fluctuations.

Instead of asking the owls to learn in one large step, we broke the problem down into small steps, said Linkenhoker, a graduate student at Stanford. We found that they could learn substantially more this way.

The feat was achieved under laboratory conditions, researchers pointed out, noting the effects might be even more pronounced in a natural setting.

An owl whose survival depends on successful orienting to its prey may display an even greater capacity for change, for instance by virtue of neuro-modulatory systems that become engaged during such Ďarousingí activities as hunting, Parthasarathy said. To glean processes involved in adult learning, Linkenhoker and Knudsen took advantage of a feature peculiar to the brains of barn owls. These noiseless, nocturnal hunters with heart-shaped faces use what they see and hear to track their prey, developing a mental map that aligns the sights and sounds of their environment. When the bird hears a noise coming from a certain location, a nerve cell in a specific region of the brain fires. The same neuron signals again when the bird sees what he just heard. The auditory and visual information is coordinated in the optic tectum, the midbrain region responsible for orienting the owl to its target. The visual map represents information submitted by the retina. The auditory map is based in part on the split-second differences between the time sounds arrive at each ear. For proper coordination of its auditory and visual worlds, the young owl must learn, for instance, that when it is looking directly at a mouse, the mouseís terrified squeak reaches both ears at the same time, Parthasarathy explained. But when the squeak reaches the right ear first by a certain number of microseconds (millionths of a second), the owl should expect to see the mouse a certain number of degrees to the right.

The animals use this map with deadly accuracy to pinpoint prey for their night time meals.

In the tests, owls were thrown for an optical loop by lenses that shifted what they saw to the left or right of the objectís actual location. Yet the researchers found young barn owls did not give a hoot about the distortion. The birdsí brains adapted to the optical shift of the visual world by gradually altering the auditory map to keep sight and sound in sync.

The older birds, however, were not able to adjust as readily, their brains making only about 9 per cent of the realignments seen in the youth group. Thus, when they looked at the world through the prism glasses, two brain regions would fire, one for the sound and the other for the sight. Convinced this adult learning impairment could be overcome by making the visual shifts more gradually, linkenhoker opted to introduce the change in small increments, shifting the view of the object first 6 degrees to the right, then 11 degrees and finally 17 degrees.

This time, the adults altered their mental maps by incorporating 53 per cent of the changes implemented by the juveniles. Although the visual-auditory map still was not perfectly coordinated, it showed a marked improvement over the disjointed effort produced by mature owls that tried to learn in one fell swoop. In fact, one owl adjusted so well to the 17-degree lenses, the researchers traded the glasses in for an even more distorting pair, one that moved the object 23 degrees. Even then, the adultís adjustment was on par with that of the juveniles.

Gaining deeper insight into how the mature brain adapts eventually could help physical therapists treat patients more effectively after a stroke or brain injury. Or, the knowledge might even make it easier for adults to learn a new language, said Knudsen, who has spent 15 years analysing the effects of large optic changes on the auditory system.

The neurosystems in the barn owl, including the formation of the visual maps, bear sufficient similarity to those in mammals, including humans, that the finding should be greeted with optimism, Parthasarathy said.

It calls into question whether other systems described as not malleable are really as fixed as we previously thought and shows we are at the beginning of understanding how changeable our brains really are, she told UNI.

A better understanding of the neural mechanisms underlying this form of plasticity in adult owls should lead to a better grasp of the limits of, and capacities for, adult learning. These experiments should offer the hope to those of us who arenít getting any younger that improving learning ability just means finding new strategies for inducing plasticity in our brains. (UNI)

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