In order to create the visual effect, the scientists used green fluorescent proteins (GFPs) which light up when calcium concentrations arise. Scientists typically use custom-made GFPs to create an image of cellular activity in real time — but until now, it hadn’t been attempted on live fish as they freely move about.
Once the GFP was developed (a genetically engineered protein called GCaMP7a), the team tested it on genetically modified zebrafish larvae, that were between four and seven days old. At this stage in their life they are still transparent, allowing the scientists to peer non-invasively into their brains.
The researchers were particularly interested in the zebrafish’s optic tectum, the area where its visual processing takes place. The researchers created a special transgenic zebrafish that expresses the protein in this particular region.
Once the fluorescent microscope was set up, the scientists conducted a series of different experiments designed to stimulate the fish’s visual processors. The first experiment involved a dot on a screen that the fish watched move back and forth, and the second involved a paramecium — a tiny organism that the zebrafish preys upon.
When the fish watched these stimuli move, the neurons flashed like waves across the brain — a pattern of lights that the scientists say corresponds to the neurological activity linked with visual processing.
And in fact, when the paramecium was motionless, the scientists recorded no activity. Incredibly, the scientists were able to track these patterns when the fish were immobilized — and also when they were allowed to freely swim around searching for prey.
Moving forward, the scientists hope to observe and map the neural activity across the entire brain, including the areas required for learning and thinking.
Check out the entire study here.