Have you ever picked up a piece of fruit and taken one deep sniff to see if it was ripe?
It turns out that mice do something surprisingly similar.
A new study has found that humans and mice use the same basic brain system to process smells, even though they sniff in very different ways.
The research, led by scientists at Northwestern University, was published in the journal Science Advances.
The findings suggest that the way mammals smell their surroundings has remained largely unchanged throughout evolution.
At first glance, humans and mice seem to use their noses very differently. Mice usually take many quick sniffs as they search for food, while humans often take one slow, deep breath to smell something. Scientists once believed these different behaviors meant the two species processed smells in different ways.
However, the new research tells a different story.
The scientists carried out two related studies. One focused on mice, while the other examined humans. Together, they found that both species rely on the same basic brain activity to recognize smells.
In the first study, researchers watched mice as they searched for food. They built a special camera system that tracked the animals’ movements and breathing at the same time.
The team noticed something unexpected. As mice picked up food with their paws, they often brought it to their noses and took one quick, deliberate sniff before eating it. This was different from the rapid sniffing they used while searching for food.
The researchers found that this “smell check” was not simply an automatic reaction to an odor. Even when the mice’s sense of smell was disrupted, they still performed the same sniffing behavior. But when scientists temporarily blocked activity in the motor cortex, the brain area involved in voluntary movement, the behavior stopped.
This showed that the mice were choosing to sniff on purpose rather than reacting automatically. In other words, they were actively gathering information about their food, much like people do.
The second study explored how humans recognize smells so quickly, even though they sniff much more slowly than mice.
Using a new, minimally invasive technique, researchers measured brain activity in healthy volunteers while they took a single intentional sniff.
The team discovered that one deep breath triggered a pattern of brain waves called theta oscillations. These slow brain rhythms appeared at the same frequencies found in rodents during sniffing.
These brain waves help organize the faster brain activity that allows the brain to identify and understand smells. Even though human sniffing is much slower, the brain still uses the same timing system seen in mice.
The researchers believe this shows that mammals share a common biological design for smelling the world around them. Over millions of years, different species have adapted the system to fit their own behavior, but the underlying brain mechanisms have remained remarkably similar.
The discovery may also have important medical benefits. Changes in sniffing behavior have been linked to conditions such as Alzheimer’s disease, Parkinson’s disease and autism. By understanding how the healthy brain processes smells, scientists may eventually develop better ways to detect these conditions earlier or improve future treatments.
The researchers say the studies reveal a simple but powerful idea: whether it is a mouse checking a food crumb or a person smelling a ripe melon, both are using an ancient brain system that has been preserved through evolution for millions of years.
Source: Northwestern University.
