This huge, green fluorescent eye does not belong to an alien, but to a zebrafish larva just a few days old. Interestingly, the brain region that controls their eye movements is very similar to the corresponding brain region in mammals. In zebrafish, however, it consists of only 500 neurons, making it a suitable model for studying human vision.
Thanks to these special properties, the above zebrafish larva and its relatives have helped to clarify an important question: How do short-term memory and vision work together? A multitude of sensory information constantly flows into our eyes, which is constantly changing. But how do we manage to focus on the essential aspects of a situation in this sensory overload? And how do we combine what we are looking at into a bigger picture – for example, several words we read into a sentence? To find out using zebrafish larvae, a research team at Cornell University examined the fish’s neural connections using an unusual approach. The researchers worked with so-called dynamic systems – mathematical models that describe how the state of a system changes over time. The current state determines the future states, just like when moving our eyes: the current visual impressions determine where we direct our visual attention next.
The researchers discovered that the dynamic system of zebrafish larvae consists of two feedback loops, each containing three clusters of closely connected cells. Based on this anatomical architecture, they were able to create a computer model that accurately predicts the activity pattern of zebrafish eyes. A surprising result for co-author Emre Aksay from Weill Cornell Medical College: “I consider myself primarily a physiologist. So I was surprised at how much of the circuit’s behavior we could predict based on the anatomical architecture alone.”
Next, Aksay and his colleagues want to investigate how the cells in the different clusters contribute to the behavior of the circuit – and whether they have different genetic signatures. In the future, this data could be used to better treat eye movement disorders and gain new insights into other brain regions that rely on short-term memory.