How Humans Navigate By Smell

Similar to desert ants or homing pigeons, people have a sense of navigation which lets us use our sense of smell to identify things, and also to get around.

Our brains are wired to convert smells into spatial information, say researchers. While humans may lack the scent-tracking sophistication of, for example, a search-and-rescue dog, we can sniff our way, blindfolded, toward a location whose scent we’ve smelled only once before, the new study shows.

Previous smell navigation investigations have been conducted with seabirds and rodents, but this is the first time researchers have field-tested smell-based navigation with humans. The results indicate we have a “olfactory positioning system”; something like a built-in GPS.

Lead author Lucia Jacobs, professor of psychology at University of California, Berkeley, said:

“What we’ve found is that humans have the capability to orient ourselves along highways of odors and crisscross landscapes using only our sense of smell.”

Orientation Olfactory

Smell is a primitive sense that our early ancestors used for foraging, hunting and mating, among other skills necessary for survival. Early sailors and aviators gave anecdotal reports of using odors to navigate, but there have been no experiential scientific studies on this until now.

The process of smelling, or olfaction, is triggered by odor molecules traveling up the nasal passage, where they are identified by receptors that send signals to the olfactory bulb—which sits between the nasal cavity and the brain’s frontal lobe—and processes the information.

A key to the connection between smell, memory and navigation is that olfactory bulbs have a strong neural link to the brain’s hippocampus, which creates spatial maps of our environment.

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

Navigating by Smellscape

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

Two dozen young adults were tested on orientation and navigation tasks under various scenarios in which their hearing, sight, or smell was blocked.

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 of the sponges were infused with essential oils such as sweet birch, anise, or clove.

In the smell-only experiment, participants were led, one at a time, into the room wearing blindfolds, earplugs, and headphones and walked in circles for disorientation purposes. They spent a minute at a specific point on the grid, where they inhaled a combination of two fragrances.

After being walked in circles again for disorientation purposes, they were tasked with sniffing their way back to the starting point where they had smelled the two fragrances.

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

Reference:

Jacobs LF, Arter J, Cook A, Sulloway FJ (2015)
Olfactory Orientation and Navigation in Humans.
PLoS ONE 10(6): e0129387. doi:10.1371/journal.pone.0129387

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.”

Illustration: Conny Liegl