How your brain decides what smells good or bad

New research reveals how the brain assigns emotional value to smells – and why it matters for health and happiness.

If you’ve ever recoiled from the smell of microwaved fish or smiled at the scent of fresh bread, you’ve experienced just how powerfully odors can stir emotions. But what makes our brains decide that a smell is pleasant – or downright awful?

A new study from researchers at the University of Florida Health reveals the neural pathways that give odors their emotional charge.

The findings provide the first detailed insight into how the brain categorizes smells as good or bad. This sheds light on why certain odors evoke such visceral reactions – and how that knowledge could eventually improve health outcomes.

Smell’s path to the brain

Dan Wesson is senior author of the study and a professor of pharmacology and therapeutics. He’s also the interim director of the Florida Chemical Senses Institute.

“Odors are powerful at driving emotions,” he said. “It’s long been thought that the sense of smell is just as powerful, if not more powerful, at driving an emotional response as a picture, a song, or any other sensory stimulus.”

The research focused on the amygdala – the brain’s emotional command center – which interacts with all of our senses. It has especially close ties to smell. In fact, the olfactory system has a more direct route to the amygdala than any other sense.

“This is, in part, what we mean when we say your sense of smell is your most emotional sense,” said first author Sarah Sniffen, a graduate research fellow.

“Yes, smells evoke strong, emotional memories, but the brain’s smell centers are more closely connected with emotional centers like the amygdala.”

Good vs. bad smells

To understand how this connection works, researchers studied mice – animals whose brains share many neurochemical similarities with humans. Like us, mice can learn to associate smells with positive or negative experiences.

By analyzing the mice’s brain activity, the researchers identified two genetically distinct types of brain cells in the amygdala that play a key role in determining the emotional value of a smell.

Surprisingly, they found that both cell types could be involved in generating either positive or negative responses. It all depended on where those cells were sending signals.

“It can make an odor positive or negative to you,” Wesson said. “And it all depends upon where that cell type projects in your brain and how it engages with structures in your brain.”

In other words, the same type of brain cell could contribute to opposite emotional outcomes depending on its connections.

Odors shape daily experience

Understanding smell responses may seem niche, but it has big implications – especially for those with heightened sensory sensitivity.

“We’re constantly breathing in and out and that means that we’re constantly receiving olfactory input,” Sniffen said.

“For some people that’s fine, and it doesn’t impact their day-to-day life. They might even think, ‘Oh, odors don’t matter that much.’ But for people who have a heightened response to sensory stimuli, like those with PTSD or anxiety or autism, it’s a really important factor for their day-to-day life.”

Scents associated with trauma, illness, or discomfort can trigger disproportionately strong responses in certain individuals. These reactions can sometimes interfere with routine activities or medical treatment.

Wesson noted how a patient’s negative association with the smell of a clinic – tied to previous transfusions – could cause intense distress.

Future scent-based therapies

Understanding the specific brain circuits behind these reactions may open the door to targeted therapies. According to the researchers, it may one day be possible to modulate the activity of these odor-processing pathways with medications.

This could either dampen distressing responses or help restore emotional enjoyment in cases like appetite loss.

“Emotions in part dictate our quality of life, and we’re learning more about how they arise in our brain,” Wesson said. “Understanding more about how our surroundings can impact our feelings can help us become happier, healthier humans.”

By demystifying the deep link between scent and emotion, this research not only advances neuroscience – it also offers a potential path toward better mental and physical well-being.

The study is published in the journal Nature: Molecular Psychiatry.

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