David Goggins
Former Navy Seal
Career Development
Bryan Cranston
Critical Thinking
Liv Boeree
International Poker Champion
Emotional Intelligence
Amaryllis Fox
Former CIA Clandestine Operative
Chris Hadfield
Retired Canadian Astronaut & Author
from the world's big
Start Learning

This is your brain on smells

A new study explores how the brain encodes different scents — a topic which scientists know relatively little about, compared to our other senses.

  • Unlike sight and hearing, our sense of smell remains poorly understood.
  • In a new study, scientists used machine learning to categorize thousands of different odors based on chemical properties.
  • By exposing mice to odors and measuring their neural activity, the scientists found that the brain more closely groups together odors that are chemically similar.

Science can tell us quite a bit about how the brain converts light and soundwaves to our sense of sight and hearing. But our sense of smell is less understood.

Scientists know that smell is based on the chemical makeup of things we encounter in the world. The nose communicates information about odor molecules to the brain's olfactory bulb, which then sends signals to the piriform cortex. This brain region then processes that information to produce our perception of smell. What's remained mysterious, however, is how the brain encodes and categorizes information about various types of scents.

A new study, published in Nature by researchers from Harvard Medical School, sheds light on the inner workings of the olfactory process.

"All of us share a common frame of reference with smells," senior study author Sandeep Robert Datta, associate professor of neurobiology in the Blavatnik Institute at HMS, told Harvard Medical School News. "You and I both think lemon and lime smell similar and agree that they smell different from pizza, but until now, we didn't know how the brain organizes that kind of information."

The researchers wanted to better understand how the brain is able to discern between related but distinct scents, such as that of a lemon and lime.

"The fact that we all think a lemon and lime smell similar means that their chemical makeup must somehow evoke similar or related neural representations in our brains," Datta said.

Illustration of multiphoton microscopy

Illustration of multiphoton microscopy

Pashkovski et al.

To investigate, the researchers created a database of thousands of odorous chemical structures, and they used machine learning to categorize them by features such as number of atoms, molecular weight and electrochemical properties. These odors were separated into three categories: high diversity, intermediate diversity and low diversity.

Then the researchers exposed different odors to mice, and used multiphoton microscopy to record neural activity in the piriform cortex and olfactory bulb. The results showed that when odors are chemically similar, so too is neural activity. In other words, the cortex emphasizes relationships between chemically similar odors, and it creates groupings for similar odors, which helps us distinguish between objects in the world.

Smell and neuroplasticity 

The results also suggest that perception of smell is flexible. For example, the team repeatedly exposed mice to a combination of two chemically dissimilar odors. Over time, images showed that the neural patterns produced by the pair of odors become more strongly correlated.

"We presented two odors as if they're from the same source and observed that the brain can rearrange itself to reflect passive olfactory experiences," Datta said. "The plasticity of the cortex may help explain why smell is on one hand invariant between individuals, and yet customizable depending on our unique experiences."

lemon, cinnamon, sugar, and star anise


The study provides some of the first information on how the olfactory cortex maps different odors. And the results also suggest that, by better understanding the chemical structure of different odors and how that mapping process works, scientists may someday be able to better control our sense of smell.

"We don't fully understand how chemistries translate to perception yet," Datta said. "There's no computer algorithm or machine that will take a chemical structure and tell us what that chemical will smell like. To actually build that machine and to be able to someday create a controllable, virtual olfactory world for a person, we need to understand how the brain encodes information about smells. We hope our findings are a step down that path."

LIVE EVENT | Radical innovation: Unlocking the future of human invention

Innovation in manufacturing has crawled since the 1950s. That's about to speed up.

Big Think LIVE

Add event to calendar

AppleGoogleOffice 365OutlookOutlook.comYahoo

Keep reading Show less

NASA's idea for making food from thin air just became a reality — it could feed billions

Here's why you might eat greenhouse gases in the future.

Jordane Mathieu on Unsplash
Technology & Innovation
  • The company's protein powder, "Solein," is similar in form and taste to wheat flour.
  • Based on a concept developed by NASA, the product has wide potential as a carbon-neutral source of protein.
  • The man-made "meat" industry just got even more interesting.
Keep reading Show less

Navy SEALs: How to build a warrior mindset

SEAL training is the ultimate test of both mental and physical strength.

  • The fact that U.S. Navy SEALs endure very rigorous training before entering the field is common knowledge, but just what happens at those facilities is less often discussed. In this video, former SEALs Brent Gleeson, David Goggins, and Eric Greitens (as well as authors Jesse Itzler and Jamie Wheal) talk about how the 18-month program is designed to build elite, disciplined operatives with immense mental toughness and resilience.
  • Wheal dives into the cutting-edge technology and science that the navy uses to prepare these individuals. Itzler shares his experience meeting and briefly living with Goggins (who was also an Army Ranger) and the things he learned about pushing past perceived limits.
  • Goggins dives into why you should leave your comfort zone, introduces the 40 percent rule, and explains why the biggest battle we all face is the one in our own minds. "Usually whatever's in front of you isn't as big as you make it out to be," says the SEAL turned motivational speaker. "We start to make these very small things enormous because we allow our minds to take control and go away from us. We have to regain control of our mind."
Keep reading Show less

How COVID-19 will change the way we design our homes

Pandemic-inspired housing innovation will collide with techno-acceleration.

Maja Hitij/Getty Images
COVID-19 is confounding planning for basic human needs, including shelter.
Keep reading Show less
Scroll down to load more…