We are primed for smell
The human body contains at least 1000 receptors for smells compared to only 4 each for sight and touch. We can discern between many different types of smells, even those we cannot describe. This makes odour-cued memories particularly poignant and distinct from other memories.
Hyperconnections to memory & emotion
Certain smells are known to trigger vivid emotional experiences, memories and associations. Freshly cut grass, cinnamon buns, the pages of an old book... can become vehicles into a different space and time. This is “odour-evoked autobiographical memory” – or the Proust phenomenon – named after French author Marcel Proust, who wrote about being transported back in time on catching the scent of a madeleine cookie dipped in his tea.
According to the Proust phenomenon, olfactory memory triggers are more evocative than other sensory triggers, producing detailed emotional memories. A reason for this may have to do with the way the brain processes smell and memory. Smell is processed and analysed neurally by the olfactory bulb which is closely connected to the amygdala and hippocampus – the memory and emotion brain centres. Their proximity may explain how smell gets associated with memory, which comes flooding back when re-encountering the smell.
Memories that don't fade
The more associations are created in our brains, the greater the possibility that different associations will overlap and be mixed up. Scientists call this interference and it is one of the explanations for why we forget. Our sense of smell is more primitive with less brain processing power behind it than sight and hearing, which are more highly developed. These senses are processed in the brain extensively, which enables a lot of abstraction. But the processing of smell is much simpler, which is why there is less chance of smell associations getting overlapped and being lost. In short, smells that we encounter leave lasting – even permanent – traces.