An interview with Prof. Chih-Ying Su on ‘Valence opponency in peripheral olfactory processing’

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Chih-Ying Su is an Associate Professor at the Department of Neurobiology at the University of California, San Diego. She studies the sense of smell or olfaction. In this interview, she talks about her most recent article, "Valence opponency in peripheral olfactory processing."

Can you tell us a brief overview of your work?

So my lab studies the sense of smell or olfaction. We use the fruit fly Drosophila melanogaster as a model organism. And we are particularly interested in how a very unique anatomical structure for that sensory neuron can contribute to information processing. 

Can you tell us a little bit about your most recent article? 

Yes, the insect olfactory receptors have a very interesting feature. The neurons compartmentalise or group together in the sensory hairs. So this is different from humans because our olfactory receptors are distributed on the olfactory epithelium. 

So compartmentalisation is relatively common for the invertebrate nervous system. And we speculate that the invertebrate nervous system is much less complex than the vertebrate nervous system. So they may have to figure out a way to process information with fewer neurons. However, insects and humans encounter the same problem because the sense of smell is quite challenging. There are a thousand volatile chemicals in the air, so we first need to detect the smell, and then we make sense of the scent.

What are the implications of this research?

Many of us like the smell of coffee and associate it with positive hedonic value. Before our work, people believe that this preference or this hedonic value requires activation of a population of olfactory receptive neurons or sensory neurons. And the activation pattern will then determine whether we like this odour or not. So here, we're talking about the innate preference, like the preference that we are born with, that does not require any teaching or association with past experience. 

But we found in the fly system that you don't need this combinatorial code - that each neuron has its intrinsic value. So some will carry positive valence, and some will carry negative valence. 

And what is really intriguing about our study is that the positive-negative valence neurons are paired together. So you have the yin and yang, and they're grouped together in the same hair, and they can inhibit each other within that hair. 

This research has a lot of exciting implications for public health. For instance, in developing mosquito traps, we can learn what is attractive to them and what is not. And so our idea is that studying a model organism will help us understand how other insects, such as mosquitoes, will then use that information to guide their thinking behaviour. So even though we are still at the very early stage, this kind of organisation - the positive valence paired with a negative valence - impacts the insect's guided behaviour.

What do you want to pursue next from this research?

So we also collaborate with a computational neuroscientist at UC San Diego, where he looks at our experimental data. He constructed a model to suggest that this kind of computation principle that happens at the first layer of sensory circuits can allow the animal to compute the composition of an odour niche. 

We know that an animal's preference for a particular odour is very sensitive to composition. So, for example, fruit flies like a specific smell of a rotten banana. So even if we, humans, think the banana smell is rotten, it may still not be attractive to the flies. So a slight difference in the composition of odour can profoundly impact the animal's behaviour. So I think the next step we want to pursue is to understand how this peripheral computation can impact behaviour.

Is there anything else you are currently working on related to this research?

So we are currently working on something that we hope can help us understand a very puzzling phenomenon. Something that smells nice at a lower concentration can be very repulsive in a higher concentration, like perfume, for example. 

So we are currently pursuing a project that can also help us understand this very common sensory phenomenon. This happens to not only us humans but also fruit flies. And we think this yin and yang pairing organisation may have something to do with that. So that's a very sneak preview of my upcoming research.

You can read and discover Prof. Chih-Ying Su’s research here.

Valence opponency in peripheral olfactory processing is published in PNAS

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