Researcher DJs for a fishy audience

A DJ and researcher at the University of Queensland has harnessed her knowledge of acoustics to design a sound system for zebrafish larvae in order to investigate auditory processing in the animals.  

PhD candidate Rebecca Poulsen, also known as BeXta, has shared bills with Bjork and The Prodigy, and remixed AC/DC and Icehouse.

While Poulsen continues her work as a trance DJ, she now spends much of her time researching neural coding at the Queensland Brain Institute.

Conventional thinking holds that fish larvae have basic hearing, however Poulsen has noted they can hear relatively high frequencies, raising questions about how their brains interpret sound and how that contributes to behaviour.

The Veterinarian spoke to her about zebrafish, autism research and gaining MC Hammer’s approval. 

What was the genesis of the zebrafish project?  

My PhD is looking at auditory processing in zebrafish, and its relevance to autism. I have a background in music production and DJing, a personal interest in autism and a passion for neuroscience. The opportunity came up in the Scott Lab at the University of Queensland to do a PhD with all three of my passions, and I was lucky enough to be awarded a scholarship. 

When I arrived at the Scott Lab, I needed to design a speaker system that delivered accurate sounds to the fish in the lab’s set up. Once I did that, I wanted to look at all aspects of sound. This doesn’t just include single frequencies, which is what is often looked at to determine hearing ranges of a species. I wanted to look at the complexities of sound, because the acoustic environment in nature is complex, and like most animals, fish need to be able to understand the sounds around them to survive. 

Why did you decide to use the zebrafish, and why larvae?  

Our lab uses larval zebrafish for lots of reasons. The fish we use are about 3mm long and their brains are very tiny, so we are able to see the entire brain under the microscope. We can see this information clearly, down to the individual firing of a brain cell [neuron]. We can then look at the activity of each cell over time and find the neurons that respond to sound. The advantages of the zebrafish as an animal model include their small size, ease of breeding, large clutch sizes, external fertilisation, fast development, and the transparency of embryos. They are not only a popular animal model for investigating behavioural domains such as learning and memory, but with advances in imaging technology, are popular for neurobiological studies as well. Many parts of the brain of the zebrafish can be linked to the human brain – it’s about 75 per cent of regions, so they are a useful tool for fundamental research and can inform research directions in mammals and humans. 

Can you describe your zebrafish sound chamber? How do you play sounds to the fish while scanning their brains for a reaction?  

We have a chamber that is quite small, that is used to image the fish in. It’s about 20mm cubed. There’s no room for a speaker in the water. Also, when you use an air speaker, there are lots of acoustic issues that arise, and it’s hard to tell what sounds actually end up reaching the fish. I designed a system that uses the chamber as part of the speaker. The speaker is stuck to the back glass wall of the chamber. The speaker and the glass wall vibrate when a sound is played, and the sound is delivered directly. 

What can be learned about autism by researching zebrafish brains?  

We have zebrafish that have altered genes, and those genes have been strongly linked to autism. We can look at auditory processing in those fish, and see what their auditory processing profile is, and what is unique about it. Because it’s the only model that can look at whole brain processes at a single cell resolution, we can build a picture of what auditory processing may look like in the deeper brain regions below the cortex…fish don’t have a cortex! We can look at differences in auditory sensitivity and filtering, which are two areas that people with autism can process differently. So far, we have done this in a zebrafish with the Fragile X linked gene, but the hope it to continue this and also look at more complex auditory processes as well. My work was the auditory component of this paper that looks at multiple senses.  

Which material did you choose to play to the fish, and why did you choose it?

The first sounds I played the fish were very simple sounds. These included many different single frequencies, sounds that are made of lots of frequencies, called white noise, and sounds with temporal differences, which is called different waveforms. These waveforms could be short sharp sounds, like a snare drum, or a sound with a gradual volume increase. I’ve played the fish a little bit of music, and although music hasn’t been the focus of this first study, it could be really interesting to look at how the brain responds to different types of music, in the future, or if music affects any neural processes, like fear. 

Has there been a point during your research where you have been surprised about what zebrafish hear?

Yes. Some people have been unsure whether fish could hear in the first place. I’m not sure it’s something people think about often. But it is interesting how they do hear, how similar some of the auditory processing is to humans, and what we can learn from them about our own hearing processes. 

I understand there has been some feedback from MC Hammer? 

MC Hammer has been following this project. We are connected on Twitter and I saw that he was really into science, and retweets science papers often. For that reason, the piece of music I played to the fish was MC Hammer’s ‘U Can’t Touch This’, with the hope that he may see the research, and even retweet it. He did this, both to the preprint that was published before peer review, and the paper that was published more recently. He called it “sparkling”. This was very exciting.

Poulsen’s paper Broad frequency sensitivity and complex neural coding in the larval zebrafish auditory system can be read at sciencedirect.com.

SAM WORRAD

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