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Lavender has a powerful scent. But could its scent have even more power than we think?

Professor Charles Claudianos, professor of neurogenetics and development, Monash University

Aromatherapies like lavender have been around for a long time in how they modify stress and anxiety in humans. What we've discovered in the honey bee is that lavender similarly changes their behaviour, their memories, even their DNA, and these studies might be potentially very useful in how we study the human brain.

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At Monash University in Victoria, beekeeper William Kwan cares for the university's community of honey bees.

William Kwan

What I find really interesting about bees is, as well as their importance for food security and pollination of a third of the food we eat, there's a lot that we can learn from the anatomy of the bee. They're very, very social animals, they have tremendous vision, and their sense of olfaction is something that has granted us many tools in understanding neurodevelopment and sensory systems.

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It's this keen olfactory sense - their sense of smell - that's made bees perfect research subjects for Professor Charles Claudianos.

Prof Charles Claudianos

The bee brain is particularly interesting because although it's anatomically different from a human brain, the fundamental mechanics of how it works are similar.

William Kwan

As a beekeeper, I've picked up that in regards to their sense of smell, they share a lot of similarities with us. In particular, the things which are pleasant for us is generally pleasant for bees - things like, you know, roses and lavender and flowering herbs.

Prof Charles Claudianos

Lavender has been used in France and in Europe for generations as a calmative. It's not only used as a calmative for bees, but also a calmative in terms of our pets and even ourselves. So, clearly, there's anecdotal evidence that there's something - you know, compounds like lavender which bees might actually see as beneficial.

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But there's one scent bees seem to hate - bananas.

William Kwan

A lot of beekeepers, as a tip and trick to promote hygienic behaviour and clean up inside the hive, they usually put a banana peel in the top of the hive and seal the lid, and the smell that the banana peel emits usually stimulates them to clean the hive a lot faster than it would without. Bees definitely do not like the smell and they can be a bit more aggressive.

Prof Charles Claudianos

We know that a compound which is the banana smell, isoamyl acetate, actually is used as an alarm pheromone in bees. We can use that information very insightfully to look at how we look at memory and learning and aggressive response in honey bees in the laboratory.

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Professor Claudianos decided to find out what was going on inside the bee's brain when it smelled lavender, particularly what was happening in its memory.

Prof Charles Claudianos

We can actually collect honey bees between days 10 and 14, before they actually gain an experience of the environment, and we put them into a little device where just their head's poking out and we start the classical conditioning experiment.

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For each bee, the scent of lavender is blown gently across its antennae, and immediately after, it's given a drink of sugar water. After just a few repetitions, the bees seem to learn to associate the smell with the reward.

Prof Charles Claudianos

If they have made that association, the bee sticks out its tongue - what we call a proboscis - and we can go back a day later and if we give it the same smell, it will put out its tongue as a positive response that it has formed a memory. We've also seen that association as long as weeks later, and considering the bee only lives for weeks or a couple of months, this is a significant part of their life.

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But are the bees' reactions to the scent of lavender just a learned association, or do they have an innate response to the scent?

Prof Charles Claudianos

By chance, when we were actually looking at memory and how memories are formed in a bee brain, we did see that there was a preference of certain odours, and it just so happens that one of these compounds ended up being the same compound which actually modifies the aggressive response in the bee.

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To identify the particular compounds which were modifying bee behaviour, Charles and his group designed another experiment.

Prof Charles Claudianos

The feather experiment, you can see it's a black feather, and black is the colour that they respond to adversely because they think it's a threat. When that spins and hits the bees, they get into an agitated state and they start stinging behaviour, and you can see here how one's raising its abdomen and probably releasing its alarm pheromone, that banana smell - isoamyl acetate.

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Charles isolated two specific scent molecules that really did make bees calmer - 2-phenylethanol, the key component of rose scent, and linalool, a common floral scent found in many varieties of plants, particularly lavender. They then replicated the experiment in the field.

Prof Charles Claudianos

And both the laboratory experiment and the hive experiment in the field proved to give the same results, so these two compounds really had a significant effect on calming bees.

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After successfully linking scent to both memory-making and mood regulation in bees, Professor Claudianos and a team of international collaborators turned their attention to what those scents were doing to the bees' DNA.

Prof Charles Claudianos

In 2006, our group was part of a large international team which sequenced the honey bee genome, and after we got the data, we actually understood that the honey bee genome was much smaller than other genomes which we had analysed previously.

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Claudianos and his research partners had a theory that the olfactory cues triggered by scents like lavender were directly linked to the expression of certain bee genes.

Prof Charles Claudianos

People might think that the genome really is only involved in how we develop as an organism. That's a misconception. The genome interacts with the environment constantly, and we now know these processes actually involve this science called epigenetics.

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When you think of DNA, you think of the classic double helix filled with genes. But not all of those genes are active. Indeed, some can be turned off.

Prof Charles Claudianos

Epigenetics is how genes are dynamically being switched on and switched off as a function of environment. And it involves certain chemical processes, in particular methylation.

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In methylation, environmental influences cause certain molecules - methyl groups - to attach to the DNA, effectively silencing particular genetic expressions. In this way, different genetic traits can be expressed in the host. Using cancer drugs designed to stop the methylation process, Charles and his colleagues were able to see what the bees could remember if they weren't able to make epigenetic changes to their DNA.

Prof Charles Claudianos

You take just a drop of these drugs, you put it just on the thorax, or the back, of the bee and it will absorb it. Then the bee is put into the same set-up in terms of the classical conditioning, memory, learning approach, and we found that these methylation inhibitors, these cancer drugs, actually significantly affected long-term memory.

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Amazingly, Charles and his research partners discovered that bees found it almost impossible to make long-term memories if they were prevented from making epigenetic changes to their DNA.

Could there be implications for human mental health?

Prof Charles Claudianos

Bees are an exceptional model for research because they have many parallels to our own human development. So, the implications to human health - there's a few.

We understand that where you have a memory problem, one of the first things to go is your sense of smell. Sensory acuity drops, whether it's Parkinson's or some forms of dementia. So we have great hopes that the research is going to be able to translate into practical uses and how we can actually think about taking that data and examining it in the context of mental health disorders.

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But for now, the next challenge is to see what effect these scents have on the human brain.

Prof Charles Claudianos

What will happen as part of this trial, well, we get a pre-scan of the brain as a control, and then we also have a scan of a brain reacting to a visual, something which elicits aggression - like, for instance, a soldier holding a gun, or a clenched fist, or a barking, aggressive dog. Then we will also pulse the odour and look at what the response is in terms of modifying the image response.

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Although it's too early to know what Professor Claudianos will find in the human brain, he expects the response to scents like lavender to be very similar to that of bees.

Prof Charles Claudianos

Like in the honey bee, we would expect to see changes in the neurotransmitter systems that are also present in the honey bee in terms of reward, where these odours work, so looking at a human brain and seeing if we get the same sort of response would be confirming that these odours actually work in the same way, which would be very, very exciting.