Olfactory memory refers to the memory of smells. Smells can bring back a lot of memories. This is because the olfactory bulb, a region of the central nervous system that processes sensory information from the nose, is part of the limbic system.
Because the limbic system is an area closely associated with memory and emotions, smells can evoke memories and trigger strong responses almost immediately.
How is the association between smells and memories formed?
The olfactory bulb has access to the amygdala, which processes emotions, and the hippocampus, the structure responsible for associative learning.
Despite the connections between structures, odors would not evoke memories, if it were not for the conditioned responses that have formed over time.
When you first smell something, you unconsciously link it to an event, a person, an object, a time or a place. Your brain forges a link between the smell and an event, associating, for example, the smell of chlorine with summer or the smell of lilies with funerals.
When you encounter the smell again, the bond is already formed and ready to elicit a memory, or even a state of mind. The smell of chlorine can make you feel happy because it reminds you of summer times in the pool with your friends.
Lilies, however, might make you inexplicably melancholy. This is, in part, why not everyone prefers the same smells: by pure association.
Since we encounter most new smells during our childhood and youth, smells often evoke childhood memories. However, we actually start making associations between smells, emotions, and memories even before we are born.
Children who have been exposed to alcohol, tobacco smoke, or garlic in their mothers’ womb often show a preference for these odors. For them, smells that may bother other babies seem normal and even pleasant to them.
The role of the amygdala
The amygdala is an almond-shaped brain structure that processes everything related to our emotional reactions. It is one of the most primitive areas of the human brain.
It is also associated with memories and memory in general, since many of our memories are related to some emotional experience.
A decade ago, Rachel Herz, an expert in the psychology of smell, and her colleagues at Brown University, tested whether there was a correlation between the emotional intensity of a memory triggered by a smell and the activation of the amygdala.
Participants first described a positive memory triggered by a particular perfume. Next, they went to the lab to participate in an fMRI experiment.
Participants were exposed to several sequences of visual and olfactory stimuli. The visual stimuli included an image of the perfume that the participant had chosen and an image of an unbranded perfume. The olfactory stimulus included the perfume chosen by the participant and the unbranded perfume.
If the stimulus elicited a memory or emotion, participants were instructed to keep it in their mind until the next stimulus was presented.
When the participants smelled the perfume they had chosen, they showed greater activation in the amygdala and parahippocampal gyrus (a region surrounding the hippocampus).
These data suggest that odors that trigger strong, emotional memories also trigger elevated activity in areas of the brain closely related to emotions and memory.
However, it is important to know that only five people participated in this study, and they were all women. To confirm these findings, studies with a larger sample of participants, including both men and women, are needed.
Several behavioral studies have shown that smells trigger more vivid emotional memories and are better at inducing that feeling of “being transported back in time” than images.
However, there have been few studies, since that of Herz and colleagues, that have explored the relationship between odor and autobiographical memory at a neural level.
The effects of smells on our perception
The positive emotional effects that smells have also affect our perceptions of other people.
In one experiment, subjects who were exposed to fragrances they found pleasant tended to give higher “attractiveness ratings” about people who appeared in photos they were shown.
However, some more recent studies show that these effects are only significant when there is some ambiguity in the photos. Whether the person in the photo is clearly very attractive or, on the contrary, extremely ugly, the fragrance does not usually affect our judgment.
However, if the person only has a “medium attractiveness level,” a pleasant fragrance will tip the balance of our evaluation in their favor. Thus, the attractive models used to advertise perfumes probably don’t need it, but the rest of us can benefit from a spray that smells good.
Unpleasant odors can also influence our perceptions and evaluations. In one study, the presence of an unpleasant odor caused subjects not only to give lower ratings to the individuals in the photos, but also to judge some drawings they were shown as less professional.
Positive smells can also have negative effects
The mood-enhancing effects of positive smells, however, sometimes work against us: by increasing our perceptions and positive emotions, pleasant smells can cloud our judgement.
In an experiment at a Las Vegas casino, the amount of money won on a slot machine increased by 45% when the place was scented with a pleasant aroma.
In another study, a shampoo that participants had ranked last in overall performance in an initial test was ranked first in a second test after altering its scent.
In another test, participants reported that the shampoo was easier to rinse off, applied better, and left their hair shinier. Only the fragrance of the shampoo had been changed.
How long does olfactory memory last?
Olfactory memory, the link between smell and recollection, varies in duration compared to other sensory memories. Studies suggest olfactory memories can last remarkably long, potentially a lifetime. Some research points to their longevity due to the direct connection between the olfactory bulb and the brain’s limbic system, responsible for emotions and memories.
While precise timelines vary among individuals and scents, certain odors trigger vivid memories from childhood or significant events, indicating a lasting impact. Factors like emotional significance, intensity, and personal associations influence how enduring olfactory memories can be. However, concrete estimates of their exact duration in the brain remain challenging due to the complexities of memory storage and retrieval.
