By John Salak –
The nose apparently knows, especially when danger is lurking about.
Researchers at Sweden’s Karolinska Institute have discovered that the central nervous system of people and other mammals is able to judge when a smell represents danger and actually triggers an avoidance response.
The Swedish team’s research went further by revealing that negative or “dangerous” smells are processed by the nervous system faster than positive smells, effectively giving the body a quick heads up about potential dangers so it can take preemptive actions.
“The human avoidance response to unpleasant smells associated with danger has long been seen as a conscious cognitive process, but our study shows for the first time that it’s unconscious and extremely rapid,” reported Behzad Iravani, the study’s first author.
The nose is apparently well-suited for the task as the olfactory organ accounts for about 5 percent of the human brain and enables people to distinguish between millions of different smells. What’s largely unrealized, however, is that a large proportion of these smells are associated with health and survival threats, such as those associated with rotten foods.
Better still, the nose isn’t just perceptive, it is nimble and quick. Odor signals, for example, are transmitted to the brain within 100 to 150 milliseconds of being inhaled. Researchers have long recognized that the ability of people and other mammals to recognize that certain smells signal danger isn’t new. What surprised the Karolinska researchers is that the intake, signaling and pre-emptive reactions are basically subconscious.
These new insights were long in development because it was difficult to measure signals from the olfactory bulb, the first part of the rhinencephalon (literally “nose brain”) with direct connections to the important central parts of the nervous system that helps detect dangerous situations and substances.
The Swedish researchers overcame this challenge by setting up experiments in which participants were asked to rate their experience of six different smells, some positive, some negative, while they measured the electrophysiological activity of the olfactory bulb.
“It was clear that the bulb reacts specifically and rapidly to negative smells and sends a direct signal to the motor cortex within about 300 ms,” said Johan Lundström, another of the study’s authors. “The signal causes the person to unconsciously lean back and away from the source of the smell.”
This firsthand feedback led Lundström and others to better understand the process and the relative importance of the nose.
“The results suggest that our sense of smell is important to our ability to detect dangers in our vicinity, and much of this ability is more unconscious than our response to danger mediated by our senses of vision and hearing,” said.
In other words, there are times when someone should stick their big nose in.