The secrets of smell: Solving crimes and saving lives
BY Jo Carlowe
1st Jan 2015 Life
Here's how our humble sense of smell is working to save lives, and many other remarkable feats.
Smell is one of the last frontiers of neuroscience
According to experts, smell is the least understood of the five senses. This is set to change. The National Science Foundation in the US has awarded £12 million to help scientists crack the code for smell.
When the research—made up of three separate projects—comes to fruition next year, it’s hoped we’ll better understand how humans and animals identify and use smells to navigate through life.
One person who’s thrilled is Duncan Boak, who has lost his ability to smell. He’s the founder of Fifth Sense, the charity for people affected by smell and taste disorders.
“We have five senses and they’re all equally important,” he states. “They all come together to help us experience the world around us.” Boak says smell loss is frequently overlooked by the medical profession—but perhaps this is now set to change.
The science of smell
From humans to bacteria, smell is universal. Animals use it to perform remarkable feats: birds to migrate across continents, and to recognise their own eggs; mice to detect stress in their peers, and we already know that smell can evoke memories in humans.
A large interdisciplinary team of US academics are working together to unlock the science of smell. It’s no easy task—odour receptors in the brain make up about three per cent of the entire genome.
At their disposal, the researchers have access to brain-imaging technology and mathematical modelling, through which they hope to better understand both the mechanics of smell and how it influences behaviour.
Odours are chemicals that move through the air, which we detect through cells in our noses (antennae in insects, and tentacles in snails) called “olfactory sensory neurons”, which then send signals to our brains.
“The brain uses this information in many different ways,” says neuroscientist Professor Nathan Urban of the University of Pittsburgh, “to differentiate between the smell of lemons and limes, or to find the source of an odour such as a campfire or gas.”
"These findings could one day allow robots to sniff out bombs, cancer or drugs"
Professor Urban and his team are focusing on how animals use smell to find resources, such as food and sexual partners. His colleague, Jonathan Victor, professor of neuroscience at Cornell University, says their findings could one day lead to the creation of algorithms that allow robots to “sniff out” bombs, cancer or drugs. And, by interfering with the way insects such as mosquitoes use odour cues to find their hosts, it may be possible to better control disease, or to limit crop damage by pests.
In a second project, scientists are trying to figure out how the brain identifies odours and attaches significance to them. So how, for example, we differentiate between a good wine or rotting food, or how a mouse knows the stench of urine from a big cat signals danger.
In order to leave no smell stone unturned, in a third project, US researchers are mapping the olfactory circuitry of fruit flies and analysing how they encode the sensations and memories of odours in their natural environment.
“The olfactory circuit of the fly is small enough to be analysed but complex enough to be interesting,” says Professor Aravi Samuel, of the Centre for Brain Science at Harvard University. He describes a “remarkable parallel” in the structure of the olfactory system in both insects and humans, suggesting these findings will have significance beyond the world of tiny critters. In fact, harnessing the full potential of smell could affect many areas of our lives.
How smell can help us
As the following examples show, smells can affect our mood, enhance our memories, and even change our behaviour.
- Smells can prevent the spread of infection. A trial set up in a surgical intensive-care unit observed over 400 healthcare workers and visitors to see if they used a hand sanitiser before entering a patient’s room. In the control group only 15 per cent did so. However, when a citrusy smell was emitted, hand-washing was boosted by almost 50 per cent.
- Smells can make us happy. When we’re happy we produce chemical compounds in our sweat, which others can smell. Dutch researchers say the scent of happiness induces a “contagion of the emotional state”, so that those around us start to feel good too. Meanwhile, experiments that compare the impact of pleasant odours with odourless placebos have found the former dramatically improves mood.
- Smell affects our perception of time. A study found that people exposed to a pleasant fragrance felt time went faster, compared to those exposed to no odour.
- Smell can improve our memory recall. Psychologists pumped a room with the smell of cassis, while playing video footage. A week later, when tested for their memories of the film, those exposed to cassis during recall recounted far more details. Music was similarly used to see if that too could be a trigger but smell was far more effective.
- Smells can prevent malnutrition. Patients convalescing from illnesses or people with early dementia sometimes lose their appetite, which can lead to malnutrition. “Ode”, an appetite-stimulation device, has been developed to provide aromatic cues, such as the smell of Bakewell tart. This stimulates the parasympathetic nervous system, creating feelings of hunger that prompt people to eat.
- Smells can save lives. Last year, a study revealed that scent profiling could be used to improve search-and-rescue missions. Scent dogs were trained to recognise the change in the odour of the living compared to the dead. Now rescue teams can deploy human-scent dogs versus human-remains detection dogs when seeking survivors during earthquakes and other disasters.
- Smell and reminiscence. It’s not uncommon for specific smells to trigger vivid memories and emotions from childhood. Incoming smells are processed by the olfactory bulb, which starts inside the nose and runs along the base of the brain, connecting directly to the amygdala (associated with emotion), and the hippocampus (linked to memory). Consequently, identical smells trigger vastly differing emotional responses. For example, most of us would associate brown sauce with a British fry-up. But for a person who grew up in Aston, West Midlands—right next to the HP factory—opening a bottle of the pungent sauce is like uncorking an entire childhood.
“As we encounter smells for the first time we link them to moments, to people or to things,” says fragrance expert Lizzie Ostrom. “When we smell the aroma again, the brain makes a fast association. That’s why oranges and cinnamon instantly remind us of Christmas.
“In fact, when we smell something, we have an emotional response to it before our brain is able to process the language or description that might accompany that response. Hence smells seem to hit us, and we feel ambushed and overcome by the strength of our reaction.”
It’s this ability to transport us back in time that has made smell a useful prompt for reminiscence therapy. But it’s not just the elderly who can benefit.
Ostrom runs “vintage scent sessions” to help people of all ages appreciate the fragrances of times gone-by.
“When I’m theming an event around a very early part of the 20th century, the fragrances are a point of enquiry to try to appreciate the past. As we go forward in time, attendees start to say, ‘Hang on, didn’t Aunt Carol wear this?’
“Once we reach the 1970s, they’re reminiscing about their own lives. People say they feel they’ve been able to revisit their old selves and deal with the ghosts of exes."
Smell loss
Imagine life without scent. For many people this is a reality. Duncan Boak, founder of Fifth Sense, believes around five per cent of the population have impaired olfactory abilities—most with “anosmia”, the technical name for smell loss, and others with “hyposmia”, which refers to a reduced sense of smell. Loss of smell can be complete, come suddenly or occur over time.
Allergies are thought to be responsible for most olfactory disorders, while others lose their sense of smell following a virus, including colds or flu. Head injuries can also cause smell loss, and occasionally people are born without smell.
“Sense of smell acts on a subconscious level,” says Boak. “It’s only when you don’t have it anymore that you realise how important it is.”
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