Neural networks in the brain consist of many different cell types that are precisely interconnected to perform computations that are the foundation for behavior. But how do you connect the exact identity of the neurons with the behavior they are responsible for? There are still technical barriers to answering this question. Neurobiologist Dr. Laura Ewell, Freigeist-Fellow of the Volkswagen Foundation, is developing a new technique to identify cells with particular patterns of activity within an intact functioning network, afterwards the scientist would be able to further examine the identified cells. This would for example help to find out more about the disease epilepsy.
Laura Ewell carries out her Freigeist-Project "Optical activity-dependent single neuron tagging in behaving animals: Linking single cell properties to behavior" at the University of Bonn, Institute of Experimental Epileptology and Cognition Research (http://eecr-bonn.de/ewell-group/). She was born in Michigan, USA and studied Science and French at the University of Wisconsin-Madison before she became a neuroscientist. She worked as a post doc at the University of California, San Diego, and was granted a Freigeist-Fellowship in 2016.
What were your first steps as a neuroscientist?
Laura Ewell: During my Ph.D. in neurophysiology, I was trying to understand how very small networks of neurons talk to each other. Basically, there are two kinds of neurons in our brains, the ones we call excitatory - they turn other neurons on. And the ones that are inhibitory, they turn other neurons off. I was interested in how signals go through networks comprising these two types of neurons. When you work at that level, you're very far away from what the brain actually does during behavior. So I became very curious about connecting these questions.
Did you change your research focus because of this curiosity?
Yes, for my post doc, I went on to study in vivo neuroscience, in which we record the activity from neurons while animals are awake and behaving. In this way we can connect the activity patterns within neural networks to specific behaviors. During most of my postdoc I was recording from the brains of animals that have epilepsy. One of my findings: There's actually a lot of heterogeneity –neurons have varying levels of impairment – in brains of animals with this disease. I wanted to find out which neurons are which.
Why is it important to know more about the neuronal cell type?
I think it's especially important in the case of disease: If we could understand the exact identity of the neurons that are sick, maybe we could develop therapies that target those. I started to think a lot about ways to label individual neurons that we're recording from in vivo. And that's what this project is about.
Please give us more details on your project.
We want to develop a novel technique to label the neurons we are recording from – using a fluorescent protein called Campari. It is both calcium sensitive and light sensitive. The calcium sensitivity means that it changes when the neuron is active. But what is special about this protein: When the neuron is active and you shine it with light, it will go through what is called a photoconversion, and it will change to a different form that makes it glow. It's a coincidence detector - because it changes its fluorescence when there is the coincidence of activity, which the brain is generating, and a light stimulus, which the experimentalist is generating. And the best thing is, when it changes fluorescence, it will do that permanently.
In this way, you can mark the neurons you are recording from?
We can take advantage of this - if we are recording from neurons and they have this protein in them, we can design a closed-loop system. Whenever that neuron is active, we stimulate the light. And hopefully, what we would then do is label it permanently.
Your main interest is using this novel technique to work on epilepsy?
Yes, exactly. I work in temporal lobe epilepsy. One of the reasons I am really interested in this type is that the seizures are manifesting in the part of the brain that make memories. This part of the brain seems very susceptible to epilepsy. And I suggest this has got to do with the mechanisms that allow us to make memories, that they are especially susceptible to hyperexcitable activity. If it will be possible to connect brain function to cellular properties, this could be an important step for treating and curing diseases, such as epilepsy, which is rooted in cellular dysfunction.
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How do you start?
We're currently cloning that protein into a virus so that we can direct it to the neurons that we're interested in. And then we'll do a whole bunch of in vitro experiments to understand what drives that photoconversion. We need to test it to really understand the parameters that determine this process so that we can control it before we start doing our in vivo experiments. The next step would be to label cells that are active in particular behaviors or pathologies and look at the type of proteins that live in that cell compared to other cells. The question always is "Is this actually a separate functional cell class?". We are kind of looking at the ‘fingerprints’ of each cell.
We might later be able to do a more in-depth search where we look at the transcriptome, which means instead of targeting specific proteins, we look at all of the proteins that this cell expresses. That would be using single-cell RNA-Sequencing, and I would be collaborating with other researchers to do this. After these important steps, we might be able to actually process the tissue after the in vivo experiment in a way in which the tissue stays alive, allowing us to do in vitro experiments in which we record from neurons in the brain slice – like I did during my PhD. This would enable us to actually look at the functional connectivity and how that differs between labeled and unlabeled cells. But that's technically very difficult, and we’ll take it one step at a time.
Where does the idea for developing this technique come from?
When you're looking at something complex, like the brain, the way you look really determines what you see. If you zoom in at the molecular level or the genetic level, you're never going to understand how the animal makes a choice at a given time because we are always kind of limited in our scope by our techniques. By developing this new technique we try to bridge these scales between networks in the awake behaving organism and single cells and the genetic makeup of those cells.
How did you hear about the Freigeist Fellowships for the first time?
I met Heinz Beck at an epilepsy conference. We have very similar research interests, but we go at these problems with different techniques. He invited me to come and work here in Germany. He was the one who first told me about the Freigeist program - and now he is my supervisor at the University of Bonn.
How did the application process go for you? Was there anything that could have helped you with it?
No. For me it was very straightforward. I can say that it was incredibly fun. It's really different than any grant mechanism I've ever applied for in the United States. Usually, in the United States, you almost have to have the results finished to be awarded the grant. In this case, I was just allowed to dream and just think, "Well, what could I do? Let's just imagine that I could do all of these things. What could I answer?"
For me it was really helpful that I had Heinz's support because, especially when we got to the point where we were getting statements from the university, I think that would have been very difficult, coming from the outside.
What does the Freigeist Fellowship mean to you personally?
It is the ability to follow a dream - to be creative. I wasn't someone who really thought of myself as a creative scientist. And it pushed me in a way that I had never been pushed before, and that was kind of delightful. Upon further reflection, I think it also means being an intellectual. And I think that's rare in modern-day academics, to be given the chance to work independently and almost free from restrains. The Freigeist Fellowship also connects you with other researchers who think similarly and also love what they do. It is a special atmosphere.
So how was your start in the German university system?
Good. What was new to me: There are a lot of "toys" around as a scientist because there is a lot of money that goes toward equipment. And that's actually really nice because you can continually get the newest technology, which facilitates amazing science. Sometimes I feel like I am in a kind of "researcher candy store". Also, I really wish I spoke German, so I am learning, langsam!
Finally what about your research group?
I’ve recruited a team of young individuals from all over the world. I have a talented technician who is helping out in the lab and, being German, helping me navigate the University admin. We have two new PhD students, excited to learn, and I hosted an ERASMUS intern for the last few months. We’re just getting rolling – so check back in a few years!
The next deadline for applying for a Freigeist Fellowship is October 11, 2018. Here you will find all the information about the Freigeist Fellowship funding initiative. The program directors Dr. Johanna Brumberg and Dr. Oliver Grewe answer questions about the fellowship program in an interview: "Freigeist-Fellows are not in the mainstream with their research projects" – Interview with the initiatives program directors.
Statement on Animal Experiments
The Volkswagen Foundation does not carry out any scientific studies or experiments. She does not commission them either. As part of her support program, she supports scientific research projects in all disciplines, especially contributions to basic research. In a very small area of funding, this may include animal testing, for example in biomedical (e. g. neuroscience) projects. A statement (in German) from the Foundation on the subject of animal experiments can be read here.