. Rats could readily distinguish between odors when a chemical had been replaced in one mixture, but when one component had simply been removed, they could not differentiate. The researchers then anesthetized the rats and inserted electrodes into their brains. Within the olfactory bulb, each smell produced a different pattern of electrical activity. But in the piriform (olfactory) cortex, a half-inch-sized area of the rat cerebral cortex, the odors that rats could tell apart produced distinct patterns of activity, while those the rats could not distinguish produced identical patterns.
Drs. Wilson and Chapuis then trained a new group of rats to discriminate between the odors the first animals couldn't tell apart by rewarding them over and over with sips water for choosing the appropriate hole. "We made them connoisseurs," says Dr. Wilson. In the rats' piriform cortex, activity patterns elicited by these similar odors were now different as well.
They trained a third group of animals to ignore the difference between odors the first rats could readily distinguish by giving them water at the same hole after exposure to either odor. This effectively dulled their sense of smell: the rats couldn't tell one smell from the other, even for a reward. Their loss of discrimination was reflected in the piriform cortex, which now produced similar electrical patterns in response to both odors.
"Our findings suggest that while olfactory impairment may reflect real damage to the sensory system, in some cases it may be a 'use it or lose it' phenomenon," says Dr. Wilson. This opens the door for potential smell training therapies that could help restore smell function in some cases. "Odor training could help fix broken noses," he says.
|Contact: Lorinda Klein |
NYU Langone Medical Center / New York University School of Medicine