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The olfactory bulb transmits smell information from the nose to the brain. The glomeruli layer represents a spatialodor map organized by chemical structure of odorants like functional group and carbon chain length. This spatial map is divided into zones and clusters, which represent similar glomeruli and therefore similar odors. One cluster in particular is associated with rank, spoiled smells which are represented by certain chemical characteristics. This classification may be evolutionary to help identify food that is no longer good to eat. Image Credit: Wikipedia.org; Patrick J. Lynch, medical illustrator

Humans, we may have a built-in GPS in our nose

Like homing pigeons, humans have a nose for navigation. Our brains are wired to convert smells into spatial information to orient ourselves.

Like homing pigeons, humans have a nose for navigation because our brains are wired to convert smells into spatial information, according to new research from the University of California, Berkeley.

While we humans may lack the scent-tracking sophistication of a search-and-rescue dog, we can sniff our way blindfolded toward a location we've smelled only once before. Research all conducted by a UC Berkeley lab and published June 17th in the journal PLOS ONE.

Similar investigations have been conducted with birds and rodents, but this is the first time smell-based navigation has been field-tested on us.

Our results evoke a GPS-like superpower one could call an "olfactory positioning system."

"What we've found is that we humans have the capability to orient ourselves along highways of odors and crisscross landscapes using only our sense of smell," said study lead author Lucia Jacobs, a UC Berkeley psychology professor who studies evolution and cognition in animals and humans.

Smell is a sense that our early ancestors and hunter gatherers today use for foraging, hunting and mating, along with other skills needed for survival. Even early sailors and aviators gave anecdotal reports of using odors to navigate. But there had been no experiential scientific studies on this until now.

Olfaction is the process of smelling. It's triggered by odor molecules traveling up our nose where receptors send them to the olfactory bulb which sits between the nasal cavity and the brain's frontal lobe.

A key to the connection between smell, memory and navigation is the olfactory bulb with its neural link to the brain's hippocampus — where spatial maps of our environment are created.

Jacobs: "Olfaction is like this background fabric to our world that we might not be conscious of, but we are using it to stay oriented. We may not see a eucalyptus grove as we pass it at night, but our brain is encoding the smells, creating a map."

Pigeons and rats are known to orient themselves using odor maps, or "smellscapes," but sighted humans rely more heavily on visual landmarks, so the study turned up surprising results.

You can try the esperiment yourself! The test location was a 25-by-20-foot room where 32 containers with sponges were placed at points around the edge of the room. Two dozen young adults were tested on their ability to orient and navigate through various scenarios in which either their hearing, sight or smell was blocked. Only two of the sponges were infused with essential oils — such as sweet birch, anise or clove.

In the smell-only experiment, study participants were led, one at a time, into the room wearing blindfolds, earplugs and headphones and walked in circles to disorient them. However, they spent a minute at a specific point on the grid, where they inhaled a combination of the two fragrances. After being walked in circles again to increase their disorientation, they were asked to sniff their way back to the starting point where they had smelled the two essential oils.

Overall, the participants in the study navigated relatively closely back to the starting point location when using only their sense of smell, as compared to when using other sensory inputs. Moreover, they were not just following one scent, but using information from both scents to orient themselves toward a point on an odor grid.

"We never thought humans could have a good enough sense of smell for this," but in retrospect the results were "as obvious as the nose on my face," said Jacobs, who will be exploring this mechanism further as a scientist selected to be on the team of the National Science Foundation's "Cracking the Olfactory Code" Ideas Lab, taking place this summer.

Abstract
Although predicted by theory, there is no direct evidence that an animal can define an arbitrary location in space as a coordinate location on an odor grid. Here we show that humans can do so. Using a spatial match-to-sample procedure, humans were led to a random location within a room diffused with two odors. After brief sampling and spatial disorientation, they had to return to this location. Over three conditions, participants had access to different sensory stimuli: olfactory only, visual only, and a final control condition with no olfactory, visual, or auditory stimuli. Humans located the target with higher accuracy in the olfaction-only condition than in the control condition and showed higher accuracy than chance. Thus a mechanism long proposed for the homing pigeon, the ability to define a location on a map constructed from chemical stimuli, may also be a navigational mechanism used by humans.

In addition to Jacobs, co-authors on the study are UC Berkeley researchers Jennifer Arter, Amy Cook and Frank Sulloway.

This work was supported by funding from National Science Foundation Electrical, Communications and Cyber Systems Grant 1028319 to L.F.J., and by the Berkeley Research Impact program for the funding of publication fees. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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