Science & Technology

Follow your nose

Those who can easily navigate new cities and unfamiliar locations might also find they have an unusually-precise ability to accurately identify a plethora of different smells, ranging from basil and cinnamon to strawberry and peppermint.

A recent study conducted at the McGill Department of Psychiatry demonstrated the surprising link between navigation and olfaction, the chemical reaction that grants us our sense of smell. To capture the experience of a student in a new area for the first time, the study asked participants to explore a virtual city and discover its important landmarks including streets, schools, and shops. To test their navigational skills, participants had to find the most direct route between different landmarks. In a separate test, the study assessed participants’ olfactory skills by asking them to identify over 40 different smells.

Using these tasks, the Bohbot Lab showed that people who have good spatial memory are also able to identify odours better. Through magnetic resonance imaging (MRI), they identified the medial orbitofrontal cortex, or mOFC, and the hippocampus as specific brain regions involved in both smelling and directing oneself. Participants who were skilled at both tasks had thicker medial orbitofrontal cortices and a higher hippocampal volume, suggesting a possible role for these regions in olfaction and spatial awareness.  

The researchers found that patients with damage to the mOFC suffered deficits in both olfaction and spatial memory, whereas damage in other brain areas had no effect, suggesting that both tasks are related to the same region of the brain.

Louisa Dahmani, the graduate student who conducted the study, explained why the seemingly-unrelated capabilities of navigation and smell are linked.

“The current research uncovers a link between spatial memory and olfaction which may find its roots in evolution,”  Dahmani said. “The theory [is] that the olfactory sense evolved for navigation purposes.”

This hypothesis is logical, Dahmani explained, given that most animals use smell, rather than vision or hearing, to navigate and find food. Black bears, for example, have an extremely refined sense of smell, which they use to hunt food up to 20 miles away. Similarly, dogs have an olfactory organ in their brains that is 40 times larger than ours. The human reliance on sight and sound is actually uncommon in the animal kingdom, which is why Dahmani was surprised by the outcomes.

“The most surprising result was that we found the existence of this link [between olfaction and spatial memory] in humans, as we don’t very often rely on our sense of smell to navigate,” Dahmani said.

Deficits in navigation and smell often occur simultaneously with some disorders, such as Alzheimer’s disease and schizophrenia. A recent study of over 3,000 seniors showed that participants who were unable to identify at least four out of five odours in a simple smell test were twice as likely to have dementia five years later. Now, with the Bohbot Lab’s conclusion, researchers are seeking to use olfactory and spatial memory tests to see whether they can identify the risk for these disorders.

“I think this is an important line of investigation as we may be able to intervene in these individuals before the disease declares itself,” Dahmani said.

Greater understanding of the links between spatial awareness and olfaction has crucial diagnostic implications. Utilizing smell tests in patients predisposed to develop certain diseases of the brain, preventative treatments could be successfully administered much earlier on in the course of the disease’s development.

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