Complete 'nonscents': Who said humans have a poor sense of smell?

Our sense of smell may not be as inferior to animals as thought, and may even be at par with the sniffing power of dogs, according to new research that busts a myth which has survived for the last 150 years.

Scientists reviewed existing research, examining data and delving into the historical writings that helped create the long-held misconception that human sense of smell was inferior because of the size of the olfactory bulb.

"For so long people failed to stop and question this claim, even people who study the sense of smell for a living," said John McGann, associate professor at Rutgers University in the US.

"The fact is the sense of smell is just as good in humans as in other mammals, like rodents and dogs," said McGann.

Humans can differentiate between maybe one trillion different odours, which is far more, than the claim by "folk wisdom and poorly sourced introductory psychology textbooks," that insist humans could only detect about 10,000 different odours, he said.

According to McGann, 19th century brain surgeon Paul Broca is the culprit for the falsehood that humans have an impoverished olfactory system.

This an assertion even influenced Sigmund Freud to insist that this deficiency made humans susceptible to mental illness, said McGann.

"It has been a long cultural belief that in order to be a reasonable or rational person you could not be dominated by a sense of smell. Smell was linked to earthly animalistic tendencies," he said.

The truth about smell, is that the human olfactory bulb, which sends signals to other areas of a very powerful human brain to help identify scents, is quite large and similar in the number of neurons to other mammals, McGann said.

The olfactory receptor neurons in the nose work by making physical contact with the molecules composing the odour, and they send this information back to that region of the brain.

"We can detect and discriminate an extraordinary range of odours. We are more sensitive than rodents and dogs for some odours," McGann said in the study published in the journal Science.

"We are capable of tracking odour trails, and our behavioural and affective states are influenced by our sense of smell," he said.

In Broco's 1879 writings, he claimed that the smaller volume of the olfactory area compared to the rest of the brain meant that humans had free will and did not have to rely on smell to survive and stay alive like dogs and other mammals.

McGann said that there is no support for the notion that a larger olfactory bulb increases sense of smell based solely on size.

The idea that humans don't have the same sense of smell abilities as animals flourished over the years based on some genetic studies which discovered that rats and mice have genes for about 1000 different kinds of receptors that are activated by odours, compared to humans, who only have about 400.

The problem with this continuing myth, McGann said, is that smell is much more important than we think.

It strongly influences human behaviour, elicits memories and emotions, and shapes perceptions.