Our sense of smell appears to be particularly good and sensitive in providing danger warnings even before other senses do.
Results from two experiments conducted by researchers at the Karolinska Institute in Sweden previously showed that the olfactory nerve fibers deep within the nose begin to process and analyze “dangerous” smells as soon as they are detected, simultaneously activating the body’s response immediately.
This is in stark contrast to our auditory and visual systems, as these systems transfer sensory responses to specialized areas within the brain for processing, leading to delays in response time and movement.
Many may be surprised because we often primarily rely on visual and auditory reactions to determine direction and make decisions. However, the rapid detection of smells can make a significant difference.
Studies on rodents have demonstrated how the bundle of olfactory nerve fibers operates. This collection of nerve cells can actively organize stimuli based on innate responses and through training.
This is particularly true when it comes to potential dangerous situations. When you smell something unpleasant or toxic, your body immediately reacts by pinching your nose or moving away from the source of the odor.
However, what is true for mice may not necessarily be true for humans. Millions of years of separate evolution have created differences between human olfaction and that of most other mammals. The olfactory system occupies about 5% of the human brain and allows us to distinguish millions of different smells. These smells can be related to health threats, such as chemical odors or the scent of spoiled food.
Olfaction occupies about 5% of the human brain.
In humans, olfaction is particularly important as it helps detect and respond to potentially harmful stimuli quickly.
Do smells trigger faster responses than other senses?
To test this, the research team selected 19 healthy non-smoking individuals to participate in a quick sniff test involving six different odors.
Some odors, such as linalool perfume or ethyl butyrate, have fruity and relatively pleasant scents. Others, like diethyl disulfide, tend to be less appealing.
Volunteers were asked to sniff each odor multiple times, and researchers measured the non-invasive olfactory response using electroencephalography (EEG). This method not only quickly provided response times but also allowed for the recording of two different types of “brain waves” generated by the nerves.
- One is gamma waves, fast waves we often use when paying attention and memorizing something.
- The second is beta waves, which are slightly slower and represent brain oscillations often used in intentional decision-making processes.
The presence of both types of waves near our olfactory nerve cells suggests that at the moment a scent stimulates the olfactory system, other parts of the brain have already begun to respond and issue processing commands.
In a second experiment with 21 volunteers, the team examined whether this initial response translated into actual bodily responses.
Two pleasant odors, strawberry and carvone (an essential oil found in mint and caraway), were compared with something unpleasant and foul-smelling, like the ethanethiol odor of rotten cabbage. After sniffing, the volunteers’ movements were measured to determine how long the scent caused a reaction.
Combining the data, it was clear that our olfactory system processes pleasant and threatening smells at different speeds. If we inadvertently inhale a noxious and potentially life-threatening odor, we take only half a second to react. If the smell is not too bad, the response will be slightly slower.
But a lot happens within that half second. Within 250 milliseconds of the smell entering the nose, two different brain waves will “combine” to coordinate the response.
If the smell is identified as a threat, the signal is sent earlier and takes about 150 milliseconds to reach the motor cortex. If the smell is not dangerous, it may take longer for the signal to arrive.
Johan Lundström, a biologist at the Department of Clinical Neuroscience at the Karolinska Institute, stated: “It is clear that the brain reacts particularly quickly to dangerous smells and sends signals directly to the motor cortex within about 300 milliseconds.”
Our sense of smell plays an important role in detecting dangers around us.
Research on visual and auditory response times has measured the entire process from detection to action. Specifically, about 150 milliseconds for auditory responses and under 200 milliseconds for visual responses.
We may take longer to identify unpleasant smells and avoid them, and it could take significantly longer if the olfactory system cannot distinguish the signals.
Lundström added: “The results show that our sense of smell plays a crucial role in detecting dangers around us, largely unconsciously, unlike our responses to dangers through sight and hearing.”
This means that we can all breathe a sigh of relief and confidently say that our nose understands us best.
This study has been published in the journal PNAS recently.
