UC Berkeley Scientists Study Sense of Smell

How the nose knows remains one of the biggest puzzles in science.

In an effort to better understand our olfaction, or smell, system, a team of UC Berkeley scientists led by psychology professor Noam Sobel discovered a mechanism in the brain that controls odor detection.

"We live in a world in which we're constantly surrounded by odors. We were trying to find out how it is that we're not constantly overwhelmed by these odors around us, or how it is that we can tune then out and focus on other things," said Christina Zelano, biophysics graduate student and lead author of the study.

In the study published in December on Nature Neuroscience online, the scientists reported that a region in the primary olfactory cortex of the brain stops an individual from noticing surrounding scents unless the level of odor is high or the person is intentionally trying to smell something.

"We ended up identifying a novel brain mechanism that functions as a gate, allowing our brain to focus on what our nose is telling us when we want it to, and more importantly, to tune it out when we're working on other things," Zelano said.

Zelano says the paper is the first to demonstrate attention in olfaction.

"In our study, we found that a frontal sub-region of primary olfactory cortex became more active when subjects were preparing for an olfactory task compared to when they were preparing for an auditory task. This is a very strong demonstration of the fact that sensory processing is an active, rather than a passive process-mammals have evolved to actively seek out the stimuli around them rather than to sit still and have stimuli thrown at them," Zelano said.

The experiment involved 20 students who were told to focus on hearing or smelling during the tests. Subjects were exposed to five different odors: bananas, roses, vinegar, cloves and lemon.

In each trial, they had a countdown to a tone which signified the students to concentrate on either the intensity of the sound or odor.

Using a functional magnetic resonance imager (fMRI) machine, Zelano and her colleagues were able to map the blood flow in the brain so they could observe which regions were activated. They discovered that while scans showed heightened sensitivity in the olfactory part of the brain when test subjects focused on smell, there actually existed inhibition of activity in the same area when subjects carried out a non-olfactory related task.

"This mechanism allows us to ignore our nose while we're focused on other things," Zelano said.

Zelano says the idea for the experiment came naturally.

"Our lab studies olfaction, and so we work in an environment full of various odors for various experiments all the time. It just becomes a natural thought eventually, ‘How come I'm not constantly overwhelmed by odors while working in this lab? How is it that I can focus on my work?'" Zelano said.

According to Zelano, who calls olfaction the "least understood of the sensory systems," the way the nose works is still a mystery compared to the other four senses.

"The idea of attention has not been explored very much in the olfactory modality, while it has been studied extensively in vision and audition. We wanted to look more deeply into attention in olfaction," Zelano said.

Recently the Nobel Prize in Medicine was awarded to professors Richard Axel and Linda Buck for their work on the human nose. The scientists revealed that the nose could identify about 10,000 scents through an intricate, complex system of genes and specialized receptors for certain odors.

It was the first time the prestigious award was given for work in olfaction.

Zelano plans to continue her work in olfaction. She wants to investigate another sub-region in the primary olfactory cortex that responded equally no matter whether the subject focused on audition or olfaction.

"I'm very curious as to what the other regions of primary olfactory cortex, which did not show this attentional modulation, are doing. There are so many things about it that I find interesting-it is not even known how our nose turns a chemical into a percept, or how the olfactory receptors work. There's a lot to explore in the field. A lot is still unknown," Zelano said.

Tags: