The nose knows: Insights from research on olfactory senses

With the help of AI, researchers can now predict how something will smell just by looking at its chemical makeup. This can mean new perfumes, improved ‘electronic noses’ to detect odours, and better food safety.

Petrichor, that fresh smell that hits your nose as the first drops of rain touch dry soil, evokes feelings of nostalgia and longing. What if you could capture this smell in a bottle to savour it? That’s just what multidisciplinary artist Indu Antony did. Indu has only recently distilled the scent of rain at her lab in Bengaluru. She has captured petrichor in a bottle, after nearly a year of collecting mud from across the city and rain samples in funnels. Indu, who grew up in Dubai, recalls that her childhood visits to India were during the monsoons, and the smell of rain has always been a presence. 

Indu is no newcomer to the world of olfactory art. During the pandemic, she realised the power of smell. Added to that was a deep awareness of the city and her immediate surroundings. Bengaluru is a hard-to-navigate city, and most people live in bubbles, isolated from the other parts of the city, she says. What if she were to archive the smells of the city? She collaborated with a wholesale fragrance marketer in a Chikpete shop to recreate the smells that mark the city. The result was Vasané, a collection of 12 vials of smells that capture the city — from the aroma of filter coffee to sandal soap, burnt cigarettes and garbage. She collated several smell profiles that people shared with her and shortlisted them to a dozen for the project. 

The artist has also worked on archiving smells of pastoral communities across South India, which was later part of an exhibition in Bengaluru. For this project, Indu had to gather samples of Deccani sheep wool and dung, among other materials, to distil pastoral smells. The sense of smell is an underrated one, Indu says, explaining how archiving different smells helps one understand a place. 

Sanjoli Mathur is an olfactory researcher, working as a Research Associate at the University of East Anglia, England. She grew up in Delhi, and a smell she associates with the city is the smell of the Saptaparni (blackboard) tree. “Describing the olfactory heritage of a place is a complex process. Delhi has multiple histories, and to be able to define its olfactory heritage would require multiple noses to tap into people’s varied personal as well as shared memories and associations triggered by the smells,” she explains.

Talking about how olfactory heritage research has changed her understanding of a place, she explains, “Even though a place might have a single ‘historically accurate’ narrative, exploring smells can add nuance and complexity to it as they uncover the personal memories of people. Much as smell can be an important element of the cultural history of a place and a people, the importance of science in olfactory archiving cannot be ignored," she says.

The knowledge that something as intangible and invisible as smells can be documented, preserved, and reconstructed using scientific and lab-based techniques has also helped Sanjoli as a researcher. 

Triggers for memories

A growing body of research has shown that odours are autobiographical memory (AM) cues. According to a 2018 study published in the journal Memory, “olfactory cues are more effective than visual cues in experimentally triggering autobiographical memories”.

When this writer asked people what smells rekindled their memories, the answers ranged from the smell of a certain face cream reminding them of their grandma to the smell of a handwash brand bringing back memories of where they lived when they were young. For someone, the ‘90s are always associated with the smell of Champak magazines and libraries. For another, the smell of old wood takes them back to a painting they made in school. 

The pandemic effect

So what happens when someone realises they can’t smell? That’s what happened during the pandemic. Suddenly, there were accounts of people unable to smell or having a reduced ability to smell. A restaurant critic for the New York Times famously wrote about how she took to “smell training” to regain her sense of smell, including using burnt oranges to bring back her sense of smell. The 'Jamaican orange remedy', which involves eating charred orange, was a viral video during the pandemic, although experts have noted there was no scientific evidence to back the claim.

Meanwhile, researchers like Associate Professor, IISER Pune, Dr Nixon M Abraham and his team found that asymptomatic Covid infections could be detected by accurately measuring the ability to smell. The team custom-built a patented olfactory-action meter, which helped them detect asymptomatic infections. 

Living with smell dysfunction

Does smell dysfunction affect one’s emotions and lead to depression or anxiety as well? Dr Nixon Abraham, who is also one of the authors of a review article published in the Mammalian Genome journal, says that it is possible because “olfactory centres in the brain are connected to the emotional centres.”

The review article, published in April this year, also notes that olfactory dysfunction is considered one of the early signs of Parkinson’s disease, affecting over 90 per cent of patients with the condition. Olfactory dysfunction often appears several years before the onset of motor symptoms and is therefore considered an early biomarker of Parkinson’s disease, it notes. 

“The loss of sense of smell has a detrimental effect on the quality of life. Well-being of an individual is significantly affected by both hyposmia (decrease in the sense of smell) and anosmia (total loss of smell),” according to the review article. 

New York-based healthcare thought leader Abhishek Suryawanshi has a condition called congenital anosmia (a person born without a sense of smell). Abhishek, who is also the Director of Wikipedia SWASTHA, says, “One of the biggest challenges with congenital anosmia is that most people simply don’t believe it’s real. Even in the US, it took me a long time to find a medical centre that could properly diagnose it and give me a certificate. In India, hardly anyone has heard about this condition. Growing up, friends and family would often tease me about not reacting to strong smells.”

Abhishek doesn’t miss having a sense of smell because he simply hasn’t experienced it. “But it does affect things like tasting food, noticing gas leaks, or enjoying festivals and traditions where smell plays a big role,” he adds. 

Growing research on smells

There’s growing research now in the field of olfaction that is indeed good news to those with smell dysfunctions. Researchers at Tufts University School of Medicine and the Graduate School of Biomedical Sciences have recently created a powerful three-dimensional mouse model of nasal tissue that sheds new light on how our sense of smell regenerates or sometimes dwindles. Their research, published in the scientific journal Cell Reports Methods, shows how two types of stem cells in the nose “communicate and support each other to develop new smell-sensing nerve tissue.”

This study could help scientists understand and repair smell loss related to disease or ageing, the researchers hope. Researchers who were part of the study say the next challenge would be to get pure olfactory tissue from humans and develop a human organoid, which can be used to screen drugs that treat people with smell dysfunctions. 

What’s the role of AI?

All talk of strides in olfaction research and no mention of artificial intelligence? Bellary-based researcher Aryan Amit Barsainyan says that most AI research has focused on vision, hearing and language. It’s only lately that AI is changing how scientists study and understand smells, he observes. “With the help of AI, researchers can now predict how something will smell just by looking at its chemical makeup (molecular structures). This means they can design new perfumes, improve "electronic noses" that detect odours, and even use smell to help with things like food safety, medical tests or creating new medicines."

Aryan works as a machine learning engineer for a US-based startup focused on developing AI tools for accelerating scientific discovery. He has been part of collaborative research projects aimed at predicting odour perception from odorant mixtures and exploring improved molecular representations that boost odour prediction accuracy.

As someone passionate about virtual reality and emerging tech, he imagines slipping on a VR headset, and suddenly being “surrounded by the sights and sounds of gentle rain, and you can actually smell that fresh, earthy scent that comes with it.” That may happen sooner rather than later, considering the strides in VR and olfaction. 

Researchers from Japanese and UK universities have collaborated to develop the world’s first cognitive training method for older adults by melding olfactory simulation and VR, according to a Scientific Reports study published in March this year. This involves a VR controller to interact with and memorise a scent and later locate the same scent in a virtual landscape. 

In yet another promising breakthrough, a research team from South Korea has now developed a “next-generation AI electronic nose” that can distinguish scents much like the human olfactory system and even analyse smells, a significant development for many industries such as healthcare and cosmetics. 

Back in 2013, Google played an April Fools’ Day prank by announcing the Google Nose BETA that promised “the sharpest olfactory experience available." Today, such an announcement is very much in the realm of the possible.

Follow the odour!

There are millions of sensory neurons in the olfactory epithelium, the tissue in the nasal cavity’s roof. These neurons contain proteins called receptors that bind odour molecules. When an odour molecule flits by, the receptors get activated. The human nose has as many as 400 odour receptors. The olfactory bulb is located in the forebrain and gets neural input about odours detected by the cells in the nasal cavity. It’s in the olfactory bulb that information about odours is processed. 

Super smeller

Joy Milne, a Scottish woman in her 70s, came to be known as a Super Smeller because she has hyperosmia, an increased sensitivity to smells. She was able to detect a change in her husband’s body odour years before he was diagnosed with Parkinson’s. This ability has led to the use of skin swabs for greater accuracy and speed of diagnostic testing for Parkinson’s.

Sniffing out the best and the worst

Not all smells are everyone’s favourite, but there are some universally acknowledged best and worst smells. According to a study conducted by scientists from the University of Oxford and Karolinska Institutet, Sweden, vanilla was the universal favourite. Participants also liked fruity scents of pineapple or peaches, flowery and spicy scents, like those of lavender, roses, and cloves. The less pleasant smells included soy milk and apple juice, followed by the “sweaty feet” scent of isovaleric acid that may be found in faeces and blood. 

Proust effect

The Proust effect or the Proust phenomenon is the intense autobiographical memories that come rushing, following intense sensory experiences, particularly involving smell and taste. The famous quote from In Search of Lost Time by Marcel Proust is often referenced while talking about involuntary memories and olfaction: “I carried to my lips a spoonful of the tea in which I had let soften a bit of madeleine. But at the very instant when the mouthful of tea mixed with cake crumbs touched my palate, I quivered, attentive to the extraordinary thing that was happening inside me. A delicious pleasure had invaded me, isolated me, without my having any notion as to its cause.”