It’s the nose that makes sense of scents

Perfume makers have long known that certain smells can mask or enhance others. Now US researchers say they have uncovered a potential mechanism for this phenomenon.

And it’s not all about the brain. The ability to distinguish between a variety of different odours begins in the nose, they found.

Using a 3D imaging method called SCAPE microscopy, a team from Columbia University monitored how thousands of different cells in the nose of a mouse responded to different odours and mixtures of those odours. 

3D imaging reveals the intact olfactory epithelium – specialised tissue – inside the nasal cavity of a mouse. Credit: Wenze Li and Lu Xu/Hillman and Firestein Labs/Columbia University’s Zukerman Institute and Columbia University.

Each such cell has one of a wide range of different sensors, or receptors – up to 400 in humans. For a pure, single odour, only the cells whose receptors are sensitive to that odour will become active, sending a code to the brain that it can identify as that odour. 

Given this, the researchers expected to see that the cells activated by mixtures of odours would be equivalent to adding together responses to individual odours. 

They found, however, that in some cases an odour could turn off a cell’s response to another odour in a mixture, while in others a first odour could amplify a cell’s response to a second odour.

The researchers say their findings, reported in a paper in the journal Science, challenge the traditional view that the brain makes sense of a mixture of scents by figuring out all of the individual components. {%recommended 10530%}

It seems the signals being sent to the brain get shaped by these interactions within the nose.

“Our results showed that scent molecules can both activate and deactivate receptors, masking other scents not by overpowering them, but by changing the way cells respond to them,” says biomedical engineer and co-senior author Elizabeth Hillman. 

“These findings could actually be very useful, for example to make better air fresheners that actually block out any unwanted smells.”

They are also exciting, says the other co-senior author, Stuart Firestein, because being able to change the way a receptor responds to a substance is important for drug development. 

“Our studies in the nose actually shed new light on possible ways to modulate the response of other cell types that might be involved in disease,” he says.

Hillman developed the SCAPE technology, which creates 3D images of living tissues in real time using angled sheets of light.

She and colleagues used this to examine neuronal cells which had been labelled with fluorescence that flashed under the microscope when they were activated. They then exposed the animals’ nasal tissues to a range of different scent combinations.

This allowed them to simultaneously analyse activity in any of the tens of thousands of single cells over long periods of time.

They generated more than 300 gigabytes of data per tissue sample – requiring them to build their own powerful data processing server and have new algorithms developed.