Do you find yourself completely lost whenever your friends go off on long-winded descriptions of a wine's aroma and bouquet? Well there may be hope for you yet, you uncultured brute. A new animal study — wherein researchers trained rats to distinguish between three very similar, albeit different, smells — suggests that with training, your sense of smell can actually improve on a neurological level. Here's how it works.
Researchers Julie Chapuis and Donald Wilson placed thirsty rats inside a box with small, snout-sized holes cut into three of its sides. Through the middle hole, Chapuis and Wilson passed short blasts of three different odors. The first scent, called "10c," comprised 10 different chemicals derived from sources like fruits, oils, and cleaning agents; the second mixture, called "10cR1" was identical to the first, except one of the 10 components was replaced by another, different chemical; and the third mixture, called "10c-1" was identical to the first, only it was missing one of the chemicals.
If the rats were blasted with the first scent (10c), they would find a sip of water as a reward at the hole in the box's left wall; but if they were blasted with a smell other than 10c (i.e. 10cR1 or 10c-1), they would be rewarded with a sip of water at the hole in the box's right wall.
The researchers quickly realized that the rats could easily distinguish between 10c and 10cR1, but that differentiating between 10c and 10c-1 (the scent missing a chemical component) proved much more difficult for the little rodents. To figure out why, Chapuis and Wilson placed electrodes inside the brains of the rats.
What they observed was very surprising. Within the rats' olfactory bulbs, each smell gave rise to a distinct pattern of electrical activity. But in the olfactory cortex, smell-specific patterns only arose for 10c and 10cR1; in other words, when the rats couldn't distinguish between 10c and 10c-1, both smells gave rise to the same patterns of electrical activity in the rats' brains.
The researchers then repeated the experiment with a new batch of rats, only this time the test subjects were trained extensively to either recognize differences in smell that the first group had overlooked, or ignore differences that the first group had been quick to recognize.
Half of the new batch were taught by the researchers to discriminate between 10c and 10c-1 by rewarding them over and over and over again for choosing the correct hole. "We made them connoisseurs," explains Wilson.
The other half, however, were trained to ignore the differences between 10c and 10cR1 that rats in the first group had been so quick to discern between. This was accomplished by rewarding the thirsty rats with water at the same hole after exposure to either odor. Without any incentive to distinguish between the two scents, the rats quickly lost their ability to do so.
When Wilson and Chapuis examined the brains of the highly trained rats, they discovered that activity patterns in the rats' olfactory cortices had shifted to reflect their refined or deadened senses; 10c and 10c-1 now gave rise to distinct activity patterns, while 10c and 10cR1 gave rise to "impaired piriform cortical ensemble pattern separation," meaning that the patterns were much harder to tell apart.
"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. "Odor training could help fix broken noses."