Smell is unique among the senses in that it enters directly deep into the brain. If we look at the major pathways travelled by the other senses, such as hearing and vision, they start at the sense organs – that is, the eyes or the ears – and move to a relay station called the thalamus, before passing on to the rest of the brain.
With smell the situation is different. Rather than visiting the thalamic relay station on its journey into the brain, smell information travels directly to the major site of processing – the olfactory bulb – with nothing in between. We do not know what stopping off at the thalamus does for the other senses, but it certainly means that signals generated in the other senses are somehow “further away” from the nexus of processing done in the brain.
Could this be part of the reason why smells are both hard to put into words, but also able to trigger deeply hidden memories? Memory research has shown that describing things in words can aid memory, but it also reduces the emotion we feel about the subject. When we come up with a story about our memories, we start remembering the story as much as the raw experience.
So with my grandmother’s toy cupboard, that particular, unique, smell was picked up by the complex smell receptors in my young nose. The smell experience of the cupboard, which I have never found a name for, travelled directly into my brain, lodging next to the part specialised for encoding experiences. There it got entangled with the other memories of the cupboard, untouched by language, difficult to think about on purpose, but still lodged in my memory. Now, years later, the smell is not only enough to relive that experience but it is also enough to pull out the rest of the memories along with it.