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In their nostalgic paean to childhood, “Stressed Out,” the musical duo 21 Pilots describes an experience most of us have had at one time or another:
"Sometimes a certain smell will take me back to when I was young. / How come I’m never able to identify where it’s coming from?"
This feeling often hits me when I’m out walking my dog on balmy summer nights. There’s a certain spot along our route where I catch a whiff of something that immediately transports me back to my past.
Try as I might, though, I’ve never been able to identify what part of my past it takes me back to. There’s a sense of recognition associated with the smell, along with a vaguely pleasant emotion. But other than these subtle hints of a remembered experience, I can find no contextual information with which to place it among my catalog of autobiographical memories. The explanation for these seemingly disembodied scent memories may lie in recent research on the way odor-cued autobiographical memories are distributed across the different phases of our life span.
It has been well-documented that autobiographical memories associated with smell are frequently more intense and emotionally tinged than memories associated with other sensory cues. This is due to the uniquely direct access smells have to the olfactory cortex, and the proximity of this area of the brain to the limbic system and the amygdala. Several recent studies, however, reveal another singular characteristic of olfactory-cued memories: In addition to arriving at the brain through different channels than other sensory information, olfactory cues tend to trigger memories from a different part of our past than those our other senses.
Many studies have shown that autobiographical memories are distributed unevenly but predictably across our pasts, constituting a “lifespan retrieval curve” comprised of three general stages:
- childhood (characterized by a period of “childhood amnesia”);
- a “reminiscence bump” between ages 10 and 30 (where the majority of our autobiographical memories cluster); and
- the years after that, which are dominated by the “recency effect,” in which retention of new memories begins to fade after one or two years.
A typical adult looking back over his or her lifetime will find that they formed the vast majority of autobiographical memories during the 20-year span between ages 10 and 30. Studies of memory retrieval with olfactory cues, however, indicate that memories involving smell deviate from this general pattern. They cluster not in the reminiscence bump, but rather in early childhood (when we were under 10 years of age). Our olfactory autobiographical memories, then, actually reach farther back into our pasts than the bulk of our other autobiographical memories.
Another distinctive characteristic of olfactory memory is evident when we compare childhood odor-cued memories to later autobiographical memories triggered by olfactory cues. Brain imaging reveals that childhood olfactory memories are related to increased activity in the olfactory cortex, while such memories from a later period of life correlate with greater activity in the left inferior frontal gyrus, an area that is associated with semantic memory processing. Subject to less semantic processing, childhood olfactory memories are quite likely more purely perceptual than autobiographical memories involving other sensory cues and events from a later period of life. In other words, when a random smell triggers a feeling of intense recognition and familiarity, it may very well simply be the experience of having smelled it before that we are remembering, and nothing more.
So the next time a few stray molecules grab you by the olfactory cortex and send you hurtling through time, just enjoy the ride—but there may not actually be a destination at the end of the line.
