As shown in the How Smell Works section of the site, upon detecting a smell the olfactory neurones in the upper part of the nose generate an impulse which is passed to the brain along the olfactory nerve. The part of the brain this arrives at first is called the olfactory bulb, which processes the signal and then passes information about the smell to other areas closely connected to it, collectively known as the limbic system.
The limbic system comprises a set of structures within the brain that are regarded by scientists as playing a major role in controlling mood, memory, behaviour and emotion. It is often regarded as being the old, or primitive, part of the brain, because these same structures were present within the brains of the very first mammals. Knowing this helps us to understand why smell plays such an important role in memory, mood and emotion.
Smell and Memory
The sense of smell is closely linked with memory, probably more so than any of our other senses. Those with full olfactory function may be able to think of smells that evoke particular memories; the scent of an orchard in blossom conjuring up recollections of a childhood picnic, for example. This can often happen spontaneously, with a smell acting as a trigger in recalling a long-forgotten event or experience. Marcel Proust, in his ‘Remembrance of all Things Past’, wrote that a bite of a madeleine vividly recalled childhood memories of his aunt giving him the very same cake before going to mass on a Sunday.
Smell and Emotion
In addition to being the sense most closely linked to memory, smell is also highly emotive. The perfume industry is built around this connection, with perfumers developing fragrances that seek to convey a vast array of emotions and feelings; from desire to power, vitality to relaxation.
On a more personal level, smell is extremely important when it comes to attraction between two people. Research has shown that our body odour, produced by the genes which make up our immune system, can help us subconsciously choose our partners – read more here. Kissing is thought by some scientists to have developed from sniffing; that first kiss being essentially a primal behaviour during which we smell and taste our partner to decide if they are a match.
It is likely that much of our emotional response to smell is governed by association, something which is borne out by the fact that different people can have completely different perceptions of the same smell. Take perfume for example; one person may find a particular brand ‘powerful’, ‘aromatic’ and ‘heady’, with another describing it as ‘overpowering’, ‘sickly’ and ‘nauseating’. Despite this, however, there are certain smells that all humans find repugnant, largely because they warn us of danger; the smell of smoke, for example, or of rotten food. This is explored in more detail on the Danger! page.
The Psychological Impact of Smell Loss
Given that our sense of smell clearly plays an important part in our psychological make-up, in addition to it being one of the five ways in which we connect with the world around us, its absence can have a profound impact. Anosmia sufferers often talk of feeling isolated and cut-off from the world around them, and experiencing a ‘blunting’ of the emotions. Smell loss can affect one’s ability to form and maintain close personal relationships and can lead to depression. An important issue here is the fact that smell loss is invisible to all but the patient; how would you know that you had met an anosmia sufferer unless they themselves told you? This is one of the reasons, alongside the general lack of understanding of the impact that smell has on our lives, why anosmia has never received much attention – you really do not know what you have got until it is gone.
Going back to the points made about the strong connection between smell and memory, it can be seen that losing one’s sense of smell can result in the loss of an important sentimental pathway to memories.
Research has shown that loss of olfactory function can be an indicator of something far more serious. Smell loss occurs with both Parkinson’s disease and Alzheimers, and studies have indicated that a diminishing sense of smell can be an early sign of the onset of both conditions, occurring several years before motor skill problems develop.