Reviewed by Dr. Michael Leon, PhD, Professor Emeritus of Neurobiology and Behavior, University of California, Irvine.
Smell can change the brain’s capacity to form and maintain memories. This is called neuroplasticity — the brain's ability to reorganize, strengthen, and in some regions regrow its connections.
Smell has this power because it reaches the brain's memory and emotion centers more directly than any other sense. Sight, sound, and touch pass through the thalamus first, a relay station that sorts signals before forwarding them. Odor signals go from the nose to the olfactory bulb and straight into the amygdala and the entorhinal cortex and then to the hippocampus.
The first thing you ever learned, you learned by smell
Smell is the first sense the brain uses to learn, and it starts working before birth. Odor compounds from the mother's diet cross into the amniotic fluid, which the fetus draws into its nasal cavity. Studies showed newborns whose mothers ate anise during pregnancy turn toward the smell of anise, while newborns whose mothers didn't either turn away or ignore it.
Within days of birth, before an infant can resolve a face across a room, it can identify its own mother by smell; when presented with a breast pad worn by its mother and one worn by another woman, a six-day-old infant orients toward its mother's scent.
Smell is the brain's original channel for learning, which is why it remains such a direct route to changing the brain later in life
Norepinephrine's role in neuroplasticity
For an experience to actually change the brain, something has to mark it as worth keeping.
That marker is a chemical called norepinephrine, also known as noradrenaline. It is released by a small cluster of cells in the brainstem called the locus coeruleus, which sends a signal to the olfactory bulb. When those cells fire, norepinephrine reaches the bulb, the incoming signal gets through, and the brain records it. This neurotransmitter is critical for early learning.
The Importance of Novelty
A scent you've smelled a hundred times doesn't have the same effect. The signal still arrives, but the brain has already filed it. Because the scent is familiar, it triggers a much weaker surge of norepinephrine.
In a study published in Neuropsychopharmacology, mice given a new odor every day improved on memory tests and grew new neurons in the olfactory bulb. Mice given the same pleasant mix of odors every day showed neither improvement nor growth, and performed about the same as the mice given no odors at all.
This is part of why babies learn through smell. To a newborn, every smell is new.
Take a breath where you are sitting and try to remember the last time you smelled something you had never smelled before. For most adults, it has been a while.
The Research Behind Smell and Learning
So what happens when you deliberately smell more? Researchers have now asked that in children, healthy adults, and people in their seventies and eighties.
German researchers gave 11- and 12-year-old students a rose scent while they studied English vocabulary at home, and again on the nights that followed. A week later, the students who had the scent made significantly fewer errors on the vocabulary test. Scent helped new information stick.
A 2022 review in Neuropsychology Review looked at 18 studies and found olfactory training associated with better global cognition, most consistently in verbal fluency and verbal learning, alongside increases in the size of olfactory and neuroplasticity-related brain regions, including the locus coeruleus, olfactory bulb, and hippocampus
Mental Health and Neuroplasticity
If activating the nose-to-brain connection improves learning and memory, why can’t it do the same for depression? It can. Dr. Leon and Cynthia Woo reviewed the evidence in Frontiers in Neuroscience in 2022 and found four human studies where added olfactory stimulation was associated with improvement in depressive symptoms.
The Bottom Line
The brain keeps changing throughout life, and smell may be one of the simplest ways to push the brain toward health instead of decline.
Olfactory stimulation can help the human brain learn new things, retrieve memories, and even improve mental health conditions through accessing the brain's memory and emotion centers.