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    Brain teaches nose new tricks

    Brain teaches nose new tricks
    By Lidia Wasowicz
    UPI Senior Science Writer
    From the Science & Technology Desk
    Published 10/23/2002 2:05 PM
    View printer-friendly version

    BERKELEY, Calif., Oct. 23 (UPI) -- The underestimated human brain once again has shown a greater-than-expected versatility, sticking its nose where many scientists thought it did not belong -- helping to teach adults how to recognize new smells.

    The prevailing view has been such lessons are reserved for the nose. But the new research demonstrates what one nostril learns can be passed on to the other. That means there must be a sharing of information by way of the brain, a scenario contradicting the current and widely held theory.

    The findings add to a growing body of evidence the adult brain is more pliable than previously thought. They set the stage for developing strategies to help the central nervous system recover from stroke and other injury, neuroscientists report in the Oct. 24 issue of the British journal Nature.

    Researchers tested reactions to the compound androstenone, which the sensitive nose can perceive as a range of scents -- from a foul odor reminiscent of dirty laundry or stale sweat to a pleasant aroma evoking sandalwood or flowers. Some 30 percent of the adult population is impervious to the smell. After sniffing the chemical repeatedly over a period of days, however, about half of the non-smellers can begin to pick up the scent.

    Using volunteers with no nose for androstenone, Noam Sobel and his University of California, Berkeley, colleagues studied individual nostrils to get a whiff of how they learn to smell. The 12 subjects were exposed to the odor through one nostril for 10 minutes a day for 21 days. The other nostril remained plugged to avoid direct contact with the chemical.

    Following the exposure, the group doubled the accuracy of both nostrils in detecting androstenone, from 25 percent before the trial to 55 percent afterward for the breathing side of the nose and to 49 percent for the plugged nostril.

    Because there is no link at the peripheral level between the nerves that take information from each nostril to the brain, there must be some exchange of information going on within the brain's olfactory structures that share input from both sides of the nose, the researchers reasoned. Otherwise, how could the blocked nostril learn to recognize the smell as well as the unobstructed one, they wondered.

    "Since the unexposed nostril learned just as well, the brain is definitely involved," said Sobel, a member of the Health Sciences Initiative, a multi-disciplinary group of researchers dedicated to solving health problems of the 21st century. "This contradicts a previous theory that olfactory learning occurs in the nose only."

    The researchers have not ruled out peripheral neural changes taking place as well, he added. The team now is looking into any involvement of peripheral neural plasticity -- the nervous system acquiring new capability.

    At least one researcher questioned the methods used, pointing out androstenone is notorious for its lingering odor, which could have hung around long after the blocked nostril was unplugged at the end of the experimental session. Thus, it might have received the same direct exposure to the scent as the unobstructed nostril.

    "Because of the chemical's enduring effects, the newly unplugged nostril gets a whiff of the scent retained in the nose, lungs, throat and elsewhere," Charles Wysocki of the non-profit Monell Chemical Senses Center in Philadelphia said in a telephone interview. The center was established in 1968 as the world's first scientific institute for research on the chemical senses -- taste, smell and chemosensory irritation.

    "The compound is notorious for sticking around," said Wysocki, who has experimented with androstenone for 22 years and who conducted the original studies on which the new research is based.

    However, John Gabrieli, professor of psychology at Stanford University in Palo Alto, Calif., described the study as well designed and found the conclusions well supported by the data.

    "It is a demonstration that what appears to be an inborn talent or deficiency is something that can be readily changed by practice," Gabrieli told UPI. "The power of learning and brain plasticity (pliability) is often greater than we imagine, even for something that at first glance looks like simply a genetic lottery."

    Indeed, the study shows how the brain can teach the nose new tricks, helping it learn to recognize subtle, unfamiliar aromas, Sobel said.

    The determination that new smells are learned in an area of the brain indicates the adult brain has more capability to change than had been thought, said Joel Mainland, co-author of the study.

    The discovery could have implications for how the brain recovers from injury. A flurry of recent studies has produced evidence that activity in the body's damaged regions can result in brain regeneration. For example, tying down the functioning arms and legs in certain stroke patients to force the use of paralyzed limbs has resulted in partial recovery of mobility in the stricken members.

    "The past view of the adult brain was as a static device where neurons undergo a pruning process so that you end up with fewer than you started out with. If too many are killed off, you get senile," Sobel said in an interview. "That major theme has been undergoing a change. We don't think of the adult brain as acquiring new sensory capabilities, but here's an example of such. People don't know to what extent they can mold or improve their sensory prowess."

    If the findings can be replicated using proper controls, they could portend some exciting implications for work with neurons in the brain and spinal cord, Wysocki said.

    "Then, what they've found is in fact very interesting," he told UPI. "Though I don't want to imply that Christopher Reeve (the "Superman" film star who was paralyzed in a fall from a horse) will be walking any time soon."

    The studies demonstrate that for the brain, practice makes perfect, the scientists said.

    "The training needs to be well targeted, and requires some focus and effort, but with that, people can accomplish some remarkable things," Gabrieli told UPI. "Not every weakness can be helped in this way, but this study demonstrates that the brain can acquire new talents in an area where it appeared to have no talent at all."

    Copyright © 2002 United Press International

    "Those who seek to predict the future... might first look to the past. The past is a mirror -- and those who ignore its sometimes dark reflection, are doomed to repeat it... Will it be those seeking redemption who shall decide the future... or will those driven only by greed and envy shape our destiny? Even a hundred years later, the outcome is still very much in doubt. .." Outer Limits(Heart's Desire)

    Learned non-use even for smells.