The sense of smell can unleash powerful emotions – that is beyond doubt. People are 'hard-wired' to remember what they smell. Receptors in tissue in the roof of the nose send signals from incoming odours to our olfactory bulb and then straight to our brain.
This short and direct connection is important as it passes scent signals quickly to two main areas: the neocortex and the limbic system. The rapid connection of the olfactory system and the brain's limbic system is the reason that fragrance evokes emotion and memories.
The initial response to a smell is often a subconscious one, as the first thing a smell does when it reaches us is to drive an unconscious emotional reaction in this part of the brain. Only later do we analyse it – and try to identify it.
Odorous molecules enter the nasal passages and activate receptors in the olfactory epithelium. This generates a complex signal pattern that begins in the olfactory bulb and continues in the piriform cortex. Signals from here travel into the amygdala and hippocampus, part of the limbic system at the centre of the brain, where the more intutitive emotional and memory associations are elicited. Signals also pass to the orbitfrontal cortex, at the front of the brain, where they are evaluated further and integrated with incoming signals from the other senses.