This month, we discuss the science and psychology of smell with Barney Shaw, author of The Smell Of
Freshly-mown grass, wood smoke, seaside air… smells have an uncanny ability to unlock emotions and memories. We discuss the science and psychology of smell with Barney Shaw, author of The Smell Of Fresh Rain
When we get a whiff of something, what is it we’re actually smelling?
It’s the light, organic molecules given off by the substance. But it’s always a cluster of molecules that you’re smelling, not a single molecule. When you smell a cup of coffee, you’re breathing in around 800 different molecules, of which about 30 contribute to the odour – it’s a kind of ‘chord’ of smell.
You often find the same molecules reoccurring in unexpected places. There’s a molecule in coffee that you also find in the smell of fresh bread, cucumber and old people’s skin.
How do these molecules get translated into smell?
The molecules are detected by the millions of receptor nerves inside our noses. There are a number of competing theories for how exactly these receptors recognise the molecules – they might be reading the shape, volume or even the vibrations of the molecules – but the signals get passed on to the brain’s olfactory bulb, just behind the eyebrows. Here, the disparate information from our receptor nerves is combined into a single pattern, which the rest of the brain – especially the piriform cortex – translates into a recognisable smell.
Why do smells have such a special power to evoke memories?
The olfactory bulb is bang next door to two important brain structures: the hippocampus, which is crucial for the formation of long-term memories, and the amygdala, which plays an important role in emotions. The close connection between these regions probably explains the unusually evocative nature of smells. In contrast, the other senses take a longer path into the brain, via a structure called the thalamus, which is not part of our brain’s emotional centre.
When you ask people for their favourite smells, the same ones crop up time and again – this is often because they’re linked to our childhood memories. But it’s also cultural. Germans adore the smell of marzipan; Japanese people think it smells of oil or sawdust. If you ask an Ethiopian herder for their favourite smells, they will probably include cow dung, while the most attractive fragrance for Mali’s Dogon people is the scent of onions.
There are also unpleasant smells that we come to enjoy because we associate them with delicious food, such as pungent cheese. If babies
are given a whiff of Camembert, they’ll wrinkle their noses. It’s something we learn to appreciate over time.
You also talk about the links between smell and mood…
The connection between emotion and smell works both ways. If you smell something disgusting, it tends to make you feel more hostile, and if you’re a naturally hostile person, you tend to be more sensitive to disgusting smells. Similarly, research has shown that people who are given something fishy to smell are more likely to be suspicious, while naturally suspicious people are more sensitive to fishy smells.
This link probably goes back to our evolutionary past, when a fishy smell might be a warning signal that something was rancid or ‘off’.
Has honing your own sense of smell changed how you experience the world in any way? Being able to recognise a broader range of smells definitely gives the world an extra dimension. I have a son who is blind, and so he’s not accessing the world through what is most people’s primary sense. He would frequently ask me questions like, “What does three o’clock in the morning smell of?” Writing this book has helped me to put what I smell into words. It’s also taught me that someone who relies more on their sense of smell than their sense of sight is getting a more emotional view of their surroundings, as well as one which has more potential to frighten, disgust and delight.
Finally, what’s your favourite smell?
Grilled bacon. But my second favourite is perhaps more unusual: the smell of hot tar being laid on a road. It’s a rich, thick smell – a blend of chocolate, bad egg and petrol. And it’s also got an edge of sulphur, which of course makes it all the more exciting.
THE SMELL OF FRESH RAIN BY BARNEY SHAW
Smells can conjure up memories due to the olfactory bulb’s location in the brain