A study has found that human sense of smell is better than previously thought. The human olfactory system is smaller than that of a dog or a mouse, so previous research claimed that humans’ sense of smell wasn’t as good as that of animals.

The new study, published May 11 in the journal Science, says otherwise. The study was conducted by neuroscientist John McGann of Rutgers University in New Brunswick, New Jersey, who believes for years scientists neglected studies on a critical and mysterious part of our minds.

Human Sense of Smell
McGann found that the human olfactory bulb is rather large compared to those of rats and mice, which are believed to possess a superior sense of smell. Also, his findings showed that the number of olfactory bulbs neurons in 24 mammal species is similar and that humans are in the middle, as our sense of smell is comparable to that of other mammals. Image credit: Purino/Shutterstock.

The study discards belief that human sense of smell is poor

The study said that people were believed to have a poor sense of smell because of an investigation conducted in the 19th century. An anatomist and anthropologist called Paul Broca compared brains across many different animals. Broca classified humans as “nonsmellers” because he believed that the evolutionary enlargement of the human frontal lobe gave people free will at the expense of the olfactory system. Broca found that the human brain’s olfactory bulbs were small when compared to the size of the brain overall, and he added that animals with larger olfactory bulbs had a better sense of smell.

Human Sense of Smell
Image credit: iStock.

“Compared to the olfactory bulbs, the rest of the human brain is very large,” said McGann, according to Science Magazine. “So if you look at whole brains, the bulbs look like these tiny afterthoughts; if you look at a mouse or a rat, the olfactory bulb seems quite big. You can almost forgive Broca for thinking that they didn’t matter because they look so small comparatively.”

Broca believed that a reason why humans had free will was that they were not forced to do things by odor. McGann said that Broca thought of smell as an animalistic thing that compelled behaviors, so he labeled humans as nonsmellers not because they could not smell, but because they had free will and could decide how they wanted to respond to odors.

The human nose can tell a trillion different odors apart

McGann questioned Broca’s theory after several studies were conducted, which discovered that human sense of smell was not as bad as people thought. He noted that a study carried out years ago found that people could tell a trillion different odors apart. Another study by the University of California, had researchers laying out a smell trail on a field, while blindfolded and earmuffed students had to follow the path using only their smell sense. That research found that the students were perfectly able to follow the trail using only their noses.

The neuroscientist believes that more research is needed to find which scents are humans most sensitive to, as sometimes an odor can be picked up faster by a human than a dog, and vice-versa. McGann noted that a previous research found that there is a component of human blood odor that humans are really sensitive to.

Human Nose
Image credit: Austin Fit.

One of the reasons that make smell distinctive is that olfactory information is not rooted through the thalamus, or the “switchboard” structure of the brain, according to McGann. The smell goes from the nose to the olfactory bulb and then it is directed to the olfactory processing area, but it can also be sent to places such as the amygdala and the hippocampal formation, which are linked with emotions and memory. McGann explained that is why sometimes a smell can cause a person to evoke strong memories. He added that another reason is that the nature of smell is very synthetic, as most smells in the world are mixtures of many chemicals.

“A cup of coffee has about 150 different chemicals…that you can smell,” told McGann to Science Magazine. “But you don’t have 150-dimensional perceptions – you just smell the coffee.”

However, people can’t think of it or label it as quickly as you can describe seeing the cup that the coffee is in, or the music that’s playing in the background,¬†added McGann.

According to McGann, there is evidence that when someone loses their sense of smell, it can impact on the overall phycological wellbeing of that person. Some associations have been reported with depression and a change in a person’s senses of attachment with others as result of losing the sense of smell. He noted that no study has found what may cause loss of smell, and there is not much a person can do if their smell capability is decreased.

Source: Science