You don't need to sign up for pricey wine appreciation classes to parse the subtle difference between the black cherry bouquet of a pinot noir and the black currant scent of a cabernet sauvignon. Just pour yourself a couple glasses and sniff. Your brain will quickly help you become a modest oenophile. It's up to you if you want to drink the lesson plan.
A new study by Northwestern University researchers shows that the brain learns to differentiate between similar smells simply through passive experience, shedding light on how we ultimately learn to identify thousands of smells from birth. The study also revealed for the first time how and where the brain modifies and updates information about smells.
In the study, researchers presented a single odor to human subjects continuously for 3 1/2 minutes. Half of the subjects received a minty odor; the other half, a floral odor. The researchers discovered that this prolonged sensory exposure induced mint (or floral) "expertise," depending on which odor the subjects had experienced. Those exposed to the minty smell were better able to differentiate between a variety of minty smells; likewise, the floral-exposed subjects could better discriminate among floral smells. In other words, study participants exposed to one minty odor became experts in other minty smells. Testing showed subjects retained their new expertise for at least 24 hours.
"When you have prolonged sensory experience with one smell, you become an expert for smells that are part of that original category," noted Jay Gottfried, M.D., assistant professor of neurology at Northwestern's Feinberg School of Medicine and the principal investigator of the study. The study will be published in Neuron December 21.
The researchers also used functional MRI techniques to measure brain activity from the subjects throughout the experiment. They found that as a result of prolonged odor exposure an area of the brain known as the orbitofrontal cortex (a region intimately involved in olfaction, emotion, and motivation) showed enhanced responses to the smells, corresponding to the subjects' improved capacity for distinguishing similar odors.
"Previously no one knew what part of the brain was responsible for this type of learning," said Wen Li, lead study author and a post-doctoral fellow in Northwestern's Cognitive Neurology and Alzheimer's Disease Center at the Feinberg School of Medicine. "We found that the magnitude of brain activity in the orbitofrontal cortex predicted how much of an olfactory expert a person would become as a result of passive learning."
"Information about an odor is not static or fixed within these cortical regions, but is highly malleable and can be rapidly updated by perceptual experience," she added. This malleability of the brain is called neural plasticity.