Failing sense of smell can be reversed through training

Scientists at NYU Langone Medical Center have found that loss of smell due to aging or disease can be reversed through training.

Although impairment in the sense of smell is associated with Alzheimer’s disease, Parkinson’s disease, schizophrenia, and even normal aging, exactly why smell weakens remains a mystery.

Now, recent laboratory research led by Donald A. Wilson, PhD, professor of child and adolescent psychiatry at NYU Langone Medical Center, has revealed how it may occur.

“We located where in the brain loss of smell may happen. And we showed that training can improve the sense of smell, and also make it worse,” Wilson stated.

Dr. Wilson and Julie Chapuis, PhD, a post-doctoral fellow, placed thirsty rats in boxes with a snout-sized hole in each of three walls and exposed them to brief blasts of odours through the middle hole.

Rats could readily distinguish between odours 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 odours 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 odours the first animals couldn’t tell apart by rewarding them over and over with sips water for choosing the appropriate hole.

In the rats’ piriform cortex, activity patterns elicited by these similar odours were now different as well.

They trained a third group of animals to ignore the difference between odours the first rats could readily distinguish by giving them water at the same hole after exposure to either odour.

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,” said 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,” Dr. Wilson concluded.