How the Brain Distinguishes Unique Scents

By Kylie Wolfe

Your sense of smell awakens you to freshly cooked bacon, lets you know when dinner is ready, and signals that a warm batch of cookies is emerging from the oven. It helps you enjoy the scents of each season both indoors and outdoors. But how does your brain distinguish one smell from the next?

To learn more about this phenomenon, researchers at New York University’s Grossman School of Medicine studied how different patterns of brain stimulation signal unique scents. Their results were recently published in Science.

Simulating and Stimulating

When scent molecules travel through our airways, they encounter the olfactory bulb which routes information about smell to the brain for further processing. Within the olfactory bulb are glomeruli, small spheres where olfactory neurons converge. The order of glomeruli activation is like a code that the brain interprets, distinguishing the smell of lemons from oranges or basil from cilantro.

Using mice engineered for optogenetics, a biological technique that activates neurons with light, researchers simulated the presence of certain smells by stimulating glomeruli in different patterns. The mice were trained to correctly identify a single odor using a lever, initiating a water reward system.

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Throughout the experiment, researchers changed the pattern of glomeruli activation, signaling a different smell. Then, they observed how the mice interpreted each change, recording the accuracy of their odor perception based on whether or not they pressed the lever.

Interpreting Results

Researchers noticed that changing the order of glomeruli activation introduced errors in odor identification. Altering which glomeruli was activated at the beginning of the series caused a 30 percent decline in accuracy. Altering which glomeruli was activated at the end of the series caused a five percent decrease in accuracy. Therefore, the team concluded that receptors activated early in a signaling pattern are more critical to scent recognition than those activated later.

This process is like playing a popular melody on a musical instrument.

“If I messed up with the first note, you have a much higher chance to misinterpret the melody than if I messed up with the 25th note,” explained Dmitry Rinberg, PhD, the study’s senior investigator, as reported by STAT News.

Opportunity for Exploration

Until now, scientists hadn’t successfully tracked individual scents. But by taking control of glomeruli activation, they could better identify essential features of odor processing.

Learning more about the brain and the way it interprets stimuli can help scientists answer other important questions, too. For example, why do we sometimes experience a diminished sense of smell when we’re sick?

This experiment serves as a model for future studies, giving scientists the opportunity to further decode our sense of smell — one glomerulus at a time.

Discussion Questions

  • Why is the order of glomeruli activation important?
  • What makes earlier glomeruli more essential to the accurate identification of a scent?
  • Write down a few questions about your sense of smell and search for answers.

Vocabulary

  • Glomeruli
  • Olfactory system
  • Optogenetics