Our sense of smell is the most effective early warning system we have
Our sense of smell is the most effective early warning system we have
Ability to detect and respond to the odor of a potential threat is a requirement for our survival and the survival of other mammalian species. Researchers at Karolinska Institutet have developed a novel technique to investigate what happens in the brain when the central nervous system interprets a smell as potentially dangerous or poisonous.
Specifically, the study found that negative smells associated with unpleasantness or unease are processed more quickly than positive smells, resulting in an avoidance response that is physical in nature.
"While it has long been assumed that the human avoidance response to unpleasant smells associated with danger is a conscious cognitive process, our study demonstrates for the first time that it is unconscious and extremely rapid," explains Behzad Iravani, a researcher at Karolinska Institutet's Department of Clinical Neuroscience and the study's first author. "
In the human brain, the olfactory organ takes up approximately 5% of the total space and is responsible for our ability to distinguish between millions of different smells. The odors of chemicals and rotting food, for example, are often associated with dangers to our health and survival. The brain receives odor signals within 100–150 milliseconds of inhaling through the nasal passage.
Measurement of the olfactory response and its quantitative evaluation
In order to survive, all living organisms must rely on their ability to avoid danger and seek rewards. The olfactory sense appears to be particularly important in humans for detecting and reacting to potentially harmful stimuli, according to recent research.
Until recently, it was unclear which neural mechanisms in humans were involved in the conversion of an unpleasant odor into avoidance behavior.
For one, there are few noninvasive methods for detecting and recording signals from the olfactory bulb, which is a first part of the rhinencephalon (literally "nose brain") with direct synaptic connections to the critical central nervous system regions that aid us in detecting and remembering potentially dangerous situations and substances. Another reason for this is a scarcity of noninvasive methods for measuring signals from the olfactory bulb.
In collaboration with the Karolinska Institutet, researchers have developed a method that will allow scientists for the first time to measure signals from the human olfactory bulb. The olfactory bulb is responsible for processing smells and transmitting signals to areas of the brain that regulate movement and avoidance behavior.
The most rapid warning system currently available
Participants in three experiments were asked to rate their experiences with six different smells, some of which were positive and some of which were negative, while the electrophysiological activity of the olfactory bulb was measured in response to each smell.
In the study, co-author Johan Lundström, associate professor at Karolinska Institutet's Department of Clinical Neuroscience, says, "It was clear that the bulb responds specifically and rapidly to negative smells, transmitting a direct signal to the motor cortex within about 300 milliseconds." In response to the signal, an unconscious leaning backward and away from the source of the odor is induced.
He goes on to say:
Our sense of smell is critical to our ability to detect dangers in our immediate environment, and a large portion of this ability is more unconscious than our response to danger mediated by our vision and hearing, according to the findings.
