What’s Your Fish Thinking?
Studying the links between brain and behavior may have just gotten easier. For the first time, neuroscientists have found a way to watch neurons fire in an independently moving animal. Though the study was done in fish, it may hold clues to how the human brain works.Glub, glub. Scientists developed a new technique that allows them to watch what freely swimming zebrafish larvae (bottom left) are thinking as they watch swimming paramecium (upper right). Credit: Akira Muto/National Institute of Genetics in Shizuoka, Japan
“This technique will really help us understand how we make sense of the world and why we behave the way we do,” says Martin Meyer, a neuroscientist at King’s College London who was not involved in the work.
The study was carried out in zebrafish, a popular animal model because they’re small and easy to breed. More important, zebrafish larvae are transparent, which gives scientists an advantage in identifying the neural circuits that make them tick. Yet, under a typical optical microscope, neurons that are active and firing look much the same as their quieter counterparts. To see what neurons are active and when, neuroscientists have therefore developed a variety of indicators and dyes. For example, when a neuron fires, it is flooded with calcium ions, which can cause some of the dyes to light up.
Still, the approach has limitations. Traditionally, Meyer explains, researchers would immobilize the head or entire body of a zebrafish larvae so that they could get a clearer picture of what was happening inside the brain. Even so, it was difficult to interpret neural activity for just a few neurons and over a short period of time. Researchers needed a better way to study the zebrafish brain in real time.
Eye on the ball. A close-up of the zebrafish optic tectum, which tracks moving objects, as it watches moving paramecium.
Credit: Akira Muto/National Institute of Genetics in Shizuoka, Japan