The imprint of odours in the human unconscious

Like Gregorio Samsa, Stephen D. woke up one fine day having suffered a metamorphosis. That morning, possibly due to the recent use of amphetamines, the smell took over his whole perceptive world . And this was what defined the life of this young man during the following days: an incredible sensitivity towards aromas. The exaltation of his sense of smell meant that everything he noticed around him was fragrant, and although he retained the rest of his senses, they all seemed to have lost importance under the empire of the nose.

For the first time, Stephen D. had the need to smell everything, he identified people by their smell before seeing them and he recognized the moods of his companions without looking at them. Not only did he become much more sensitive to all odors: all layers of reality became very powerful olfactory stimuli. Moreover, this metamorphosis also meant entering a reality in which a strong emotionality tinged everything , making the here and now come to the fore while abstract thought became smaller as it dissolved into this rich range of sensations.

Unfortunately, after three weeks everything went back to normal. The loss of this gift, as abrupt as its arrival, was a strong emotional blow. Once the door to a world of such pure perception was opened, it was difficult to give up those feelings.

These events, narrated by Oliver Sacks in a chapter called The dog under the skin , are presented as true by the author (Sacks, 2010/1985). To most of us, however, this may seem like an almost alien story, something that bears little or no relation to our everyday experience. In general, we believe that smell is something like the poor brother of the five senses . This is true to a certain extent.

Smell, emotionality and unconsciousness

Our whole life seems to have audiovisual format : both our leisure time and the people we relate to and the situations in which we are involved are defined by what we can see and hear. However, the story of Stephen D. has a particularity which calls into question this rule: this young man sees his sensitivity to odours increase due to the effects of a drug, but the large structures of his body do not undergo any transformation.

Neither his nose is enlarged nor his brain is transformed into that of a dog, and the changes appear and disappear very quickly, suggesting that they are due to a relatively superficial alteration. Simply put, his nervous system works differently for three weeks on top of the brain mechanisms that are already there.

Perhaps it is all explained by the fact that, in Stephen’s case, some processes that normally remain unconscious have made the leap to consciousness. Perhaps, although we don’t realize it, all of us have a dog under our skin, an unconscious part of us that reacts to smells beyond our control.

The scientific evidence seems to support this perspective. Today we know that the sense of smell is of crucial importance in our lives even though we do not realize it. For example, it has been proven that smell is a powerful trigger of memories associated with each of the fragrances, and that this happens regardless of our willingness to remember something. Moreover, the experiences that smells bring back to us are much more emotional than memories evoked by images or words (Herz, R. S., 2002). This occurs with a wide variety of smells.

However, perhaps the most interesting repertoire of reactions we have to smell is when that smell comes from another human being. In the end, the information provided by other people is just as important, if not more so, than that provided by a ripe pear, a mown lawn or a plate of macaroni. If we want to understand how communication between people based on smell works, we have to talk about pheromones and signature smells .

Invisible communication

A pheromone is a chemical signal emitted by an individual that alters the behavior or psychological disposition of another individual (Luscher & Karlson, 1959). They are chemical signals defined by each specific species and which produce instinctive reactions. Signature odours, on the other hand, serve to identify each specific member of the species and are based on the recognition of previously experienced odours (Vaglio, 2009). Both occur everywhere in many forms of life, and the case of humans does not seem to be an exception.

Although the human species is not as sensitive to odours as other mammals (a sign of this is that our nose has flattened out drastically, giving rise to fewer olfactory receptors), our body is capable of knowing aspects of other people such as their identity, their emotional state or other aspects of their psychology from these “traces” that we leave in the air.

For example, a study from 2012 showed how people can become emotionally synchronized through the smell they emit. During the experiment, a number of men were exposed to two types of film: one was scary, and the other showed repulsive images. While this was happening, samples of the sweat were collected from these participants (overall, it must have been quite an unsettling experience). Once this was done, these sweat samples were exposed to a group of women volunteers and their reactions were recorded: those who smelled sweat secreted during the vision of the scary film showed a facial gesture associated with fear, while the language of the face of those who smelled the rest of the samples expressed disgust (de Groot et al, 2012).

Despite this, perhaps the most important property of these odor trails is their ability to influence our reproductive behavior. The olfactory acuity in both men and women increases when we reach puberty (Velle, 1978), and in the case of women this capacity to perceive odors fluctuates with their menstrual cycle (Schneider and Wolf, 1955), so the relationship between sexual behavior and smell is evident. It seems that men and women judge people’s attractiveness partly by their smell, since it provides relevant information about the internal state of our bodies, an area about which sight and hearing cannot provide much (Schaal & Porter, 1991).

Women, for example, seem to prefer couples with a different repertoire of immune responses than their own, perhaps to breed offspring with a good cast of antibodies (Wedekind, 1995), and are guided by smell to receive this type of data. Beyond matchmaking, moreover, mothers can differentiate their babies’ signature scent two days postpartum (Russell, 1983). Babies, on the other hand, from the first months of life are able to recognise their mother by smell (Schaal et al, 1980).

The explanation

How is it possible that smell has such an influence on our behaviour without us noticing it? The answer lies in the arrangement of our brain. It should be noted that the parts of the brain responsible for processing information about the chemical signals around us are very old in our evolutionary history, and therefore appeared much earlier than the structures associated with abstract thinking. Both smell and taste are directly connected to the lower part of the limbic system (the “emotional” area of the brain), unlike the other senses, which pass first through the thalamus and are therefore more accessible by conscious thought (Goodspeed et al, 1987) (Lehrer, 2010/2007).

For this reason the chemical signals we receive through the nose act drastically on the regulation of emotional tone , even though we do not realize it, and that is why smells are a unique way to affect people’s moods even if they do not realize it. Furthermore, as the limbic system includes the hippocampus (a structure associated with memories), the signals collected by the nose easily evoke experiences already lived, and they do so by accompanying this memory with a great emotional charge.

All this means, of course, that theoretically some kind of manipulation could be exercised on the rest of the people without them being able to do much to control their own feelings and psychological dispositions. The clearest example of this principle of manipulation can be found, of course, in bakeries. Let’s hope that the big manufacturers of televisions and computers take a little longer to discover it.

Bibliographic references:

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