Who would have thought that your sense of smell and your ability to navigate are related? Though this appears to be a somewhat random connection, neuroscientists published a study this month suggesting that these two traits are biologically linked, where individuals who have an acute sense of smell often have an excellent sense of direction, and vice versa.
In the past decade, evolutionary scientists have proposed that the main purpose of olfaction, or our sense of smell, is to aid in navigation. This hypothesis makes sense for animals. If a polar bear — one of the world’s most acute smellers — scent-marks its tracks or territory, it can more easily find its way back to its original spot. Smelling has also been found to help other animals in long-distance navigation. In 2017, researchers from universities in Oxford, Barcelona and Pisa found that a bird’s sense of smell plays a vital role in its ability to navigate long distances over an ocean.
Though studies investigating smell and navigation have been conducted on a variety of species, few have examined humans until one published this month. In this investigation, Louisa Dahmani and her colleagues at McGill University tested the relationship between olfaction and navigation in college-age individuals. To do so, the research team examined participants’ senses of smell, their ability to navigate, and the relative volumes of brain regions associated with these two traits.
The first part of the study consisted of assessing subjects’ sense of smell. In this section, the subject was asked to sniff odor-infused felt-tip pens and identify the smells based on four multiple-choice options. Examples of smells included grass, chocolate, ginger and lavender.
To study navigation, participants were tested on their ability to navigate through a virtual town that included streets, buildings, and eight landmarks marked by signs, such as a school or movie theater. Participants were first allowed to explore the town for 20 minutes so they could learn spatial relationships between the different landmarks, enabling them to construct a cognitive map of the virtual town. Afterwards, participants were tested on their ability to navigate from one landmark to another using the most direct route.
Through both of these tests, researchers found that those who were the best at smelling tended to be the best at navigating.
In addition to testing the subjects’ skills in navigation and olfaction, the research team also used neuroimaging to gather biological evidence for the correlation between olfaction and navigation. In particular, the team examined the relative sizes of the orbitofrontal cortex, which mediates our sense of smell, and the hippocampus, which is involved in both smelling and navigation. Both regions of the brain were found to be larger in participants that demonstrated a superior sense of smell and an adept ability to navigate through the virtual maze. Scientists then concluded that a biological link does in fact exist between olfaction and navigation.
Examining brain region volume alone isn’t enough to prove that sense of smell and navigation are linked. Researchers also studied a separate group of individuals who had damaged orbitofrontal cortices. They determined that these subjects had impaired olfaction and navigation, which further strengthened the hypothesis that the two processes were linked.
So, why does it matter that these two senses are related? For one, it offers insight about the original function of olfaction — that is, to aid in navigation. It also provides an explanation as to why the sense of smell is so important that it has persisted in organisms through time. On the surface, we might not consider our sense of smell to be very important. Sure, it’s useful for smelling burnt toast, but it turns out that it can also help us in ways we never considered — like finding our way through a new town or even a crowded room.