I can never unlearn the association between garlic and freshly cut apples. I grew up in an Asian household, which means knocking on doors wasn’t exercised. Around 5 p.m. every day, my dad barged into my room with freshly cut apples while my mom prepared dinner. She loved cooking with garlic—it was a staple ingredient in her recipes. It’s funny how Asian parents show love to their kids. They choose the most obscure ways to show they care. For me, it was that bowl of garlic-stained apples that tasted like an abundance of love.
The smell of garlic and the sight of cut apples bring up more than just snippets of my childhood. They also bring many memorable events. Like the time I argued with my dad as an angsty teen, or the time my mom lectured me about messing with my sister’s books. Or even when I failed my Chinese test for the first time and had to take a stern scolding from my dad. When I see apples, I smell garlic and the same memories play in my head. But why does this happen?
The “Proust effect,” coined after French author Marcel Proust, describes a sensory experience that triggers a rush of forgotten memories. In 1977, psychologists Roger Brown and James Kulik conducted a study that observed how humans can recall highly detailed recounts of their days. Most participants in the study were able to remember their days with perceptual clarity due to highly emotional events that occurred on a particular day. Brown and Kulik later coined the term “flashbulb memory” as a “highly vivid and detailed ‘snapshot’ of a moment.”
A flashbulb memory forms when a shocking or surprising event happens in our day-to-day life. This event is so strong that it registers in our long-term memory like a picture in an album. But where does the sense of smell kick in?
Previous studies show that the link between memory and our olfactory senses exceeds those evoked by our sense of sight. In a study that explored the effects of ambient odour on brain activations during memory recall, researchers presented 32 pictures to participants—half of which had an odour associated with them—under functional magnetic resonance imaging.
“We saw a greater activation in brain activity when we encode memories with smell in our subjects compared to no-odor conditions,” writes Emmanuel Galliot, the lead author of the study. “There is no doubt a complex link between the networks involved with episodic memory and encoding with odors as context.”
Famous patient H.M. and psychologist Brenda Milner helped us understand the importance of the hippocampus and frontal lobes for memory formation. The olfactory bulb, which receives and translates odours into neural inputs, lies at the base of the hippocampus. Inside the olfactory bulb is the piriform cortex, an important structure that helps us decide whether a smell is “good” or “bad.” For example, we can tell when a cake smells tasty, or when the two-week-old meat in the fridge smells weird, or even the shampoo of that special someone smells heavenly.
Researchers from Ruhr University believe that some memories may be saved in the piriform cortex to make these judgements. They demonstrated the role of the piriform cortex in information encoding through direct stimulation. “We successfully induced changes in memory connections of mice brains by stimulating this area directly. As long as there’s instructions from the orbitofrontal cortex, long-term memory can be stored right in this area of your smell center,” writes Christina Strauch, the lead author of the study.
We all know the cliché “don’t judge a book by its cover,” but perhaps it’s better to judge it by its smell—or at least, remember it for its smell. The next time you get a whiff of the musty scent of books and think of memories of you as a kid reading comics, or a sniff of perfume that reminds you of your crush, you can thank your sense of smell for intertwining your memories with odours.
From encoding these events to retrieving them, your olfactory senses play an important role. For me, the smell of garlic and apples encoded specific memories of my arguments with my dad. The highly emotional factor of the event helped store it in my long-term memory as a flashbulb memory. Whenever I smell the combination of apples and garlic, it retrieves this specific memory—like a marker for a certain page in a book or a photo album.