About digital swarm partners and neural networks  

Otto Hahn Medal honors Johannes Kappel for outstanding research  

June 12, 2024

How does a dot become a conspecific? In fact, it proved to be enough for a virtual dot to move like a fish. Other fish perceive the specific motion pattern as a conspecific and follow the digital swarm partner. When Johannes Kappel joined Herwig Baier's department at the Max Planck Institute for Biological Intelligence in 2018, he wanted to uncover the neural basis of this process. For his discoveries, he has now been awarded the Otto Hahn Medal. In an interview, he explains what he found out, what the medal means to him, and why he conducted his research with digital swarm partners instead of real ones. 

Johannes, what have you discovered through your research?  
Together with a team of researchers, we were able to identify a specific neural circuit in the brain of zebrafish. This circuit converts perceived motion patterns typical of zebrafish into a behavioral response of social attraction: The fish follows its partner.  

What is special about that?  
Little is known about the interplay between visual stimuli and social behavior. For the first time, we have identified a circuit that extends from the retina of the eye to the depths of the brain. If we experimentally switch off the visually responsive neurons, social behavior is measurably disrupted. This underscores the importance of this circuit for conspecific recognition. 

Was there an Aha! moment during the research?  
We actually thought it unlikely that a single circuit that specifically detects conspecifics could be anatomically localized. It was all the more surprising when my data indicated for the first time that this might indeed be the case. I still remember the moment when the cluster of neurons caught my eye in the first analysis of the imaging data.  

What is it about digital swarm mates? 
A number of factors could be involved in recognizing a conspecific. For example, the color or texture of the fish. From a previous study by my research partner Johannes Larsch in our department, we knew that the specific movement pattern alone was sufficient to recognize conspecifics. However, this does not exclude other features. Using a virtual dot, we were able to isolate the motion pattern as the key stimulus. By limiting the parameters like this, we were able to study the neural processing of this very specific sensory input. 

Do all zebrafish follow such digital conspecifics in the same way?  
Good question! No, and this phenomenon is actually being investigated in further studies: Social behavior varies according to heritable genetic predispositions, the internal state of the fish, and the individual character of each animal. However, this is not my project, but that of my research partner Johannes Larsch, who has accepted a professorship at the University of Lausanne. 

What are you investigating now?  
I have started a postdoctoral position at the Friedrich Miescher Institute for Biomedical Research in Basel, where I am investigating the navigation system of zebrafish. For example, I want to understand how a fish visually recognizes objects and anchors them as landmarks in a cognitive map in the brain.   

What does the Otto Hahn Medal mean to you?  
It is a great honor and will certainly help me with my further scientific career. First and foremost, however, I was delighted to receive such a recognition for the really hard work that goes into such a doctoral thesis. In a way, I was lucky that we found out something so exciting that was also published in the scientific journal Nature. In other cases, the work behind scientific findings often goes unseen. 


The interview was conducted by Magdalena Warner. 

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