The Karolinska Institute in Sweden recently conducted two studies on how smell can warn people of impending danger. Furthermore, the olfactory bulb (bundle of nerves in the nose for detecting smell) could process negative smells at once, making the body respond quickly to danger.
The olfactory bulb, which occupies nearly 5% of the brain, enables humans to differentiate various smells. It also helps us dictate odors that could be bad for our health, such as the smell of toxins or rotten food. This new study shows that the signals elicited from these smells reach the brain in 100-150 milliseconds.
According to Behzad Iravani, a lead study author and researcher at the Department of Clinical Neuroscience, scientists have for a long time thought that the reaction of human beings to negative smells is entirely conscious. However, this new study shows that the process is swift and unconscious.
How researchers conducted the study
The researchers gathered 19 non-smokers and asked them to sniff six things. The participants considered scents such as the linalool’s perfume or ethyl butyrate pleasant. However, smells like the diethyl disulfide, which has a garlic smell, were less appealing.
While presenting them with these samples to sniff, they observed the reaction of their olfactory bulbs using electroencephalography. This process allowed the researchers to evaluate the timing of the responses. They also noted two types of brain waves that the reaction produced.
The body reacts faster to negative smells
One type of brain wave they found was the gamma wave. These waves were fast-processing and relied on attention and memory. The beta waves, on the other hand, were slightly slower. This brain wave is for intentional decision-making. Researchers concluded that having these waves close to nasal neurons proves that after the olfactory bulb is triggered, part of the brain, such as the motor cortex, begins to react.
Researchers found that it took about 150 milliseconds to get to the motor cortex when the body thought the smell was a threat. Johan Lundström, a biologist and study author from the Karolinska Institute’s Department of Clinical Neuroscience, states that the bulb specifically reacted to harmful odors and sent signals to the brain’s motor cortex in a short amount of time.
