Scientists Observe What Fish Think About

Scientists, for the first time, have seen the brain activity of a fish watching its prey.

Researcher Koichi Kawakami, of Japan's National Institute of Genetics, and his colleagues developed a very sensitive fluorescent probe to detect the neuronal activity of living fish. Looking at the neuronal signals would help understand how the brain perceives the outside world.

The basic design and function of a zebrafish brain is like the human brain. Zebrafish larvae have translucent heads which allow researchers to look into their brains.

For their study, the research team monitored the neuronal activity at single-cell resolution in the zebrafish brain, using the fluorescent marker.

They developed a genetically engineered protein called GCaMP7a that lights up under a fluorescent microscope when neurons, or brain cells, fire. The research team bred transgenic zebrafish that would be able to communicate this protein in a brain region called the optic tectum. This is the region in the brain which controls the eye movements of the animal when it looks at something that moves in its environment, reports Live Science.

When the zebrafish looks at a prey, neural signals could be seen flashing through the fish's brain, tracking the prey's movements. In this case, the research team mapped the fish's brain activity as it looked at swimming paramecium prey and swam toward it. They were able to correlate the brain activity with that prey's capture.

The new method will help in understanding which brain circuits are involved in complex behaviors, from perception, to movement, to decision making, said the researchers.

While earlier studies have imaged the single-cell brain activity in zebrafish, this is the first time that researchers have detected the neuronal activity of a freely swimming fish perceiving a natural object. "In the future, we can interpret an animal's behavior, including learning and memory, fear, joy, or anger, based on the activity of particular combinations of neurons," Kawakami said.

The new approach could possibly be used to screen chemicals that affect neuronal activity in the brain. "This has the potential to shorten the long processes for the development of new psychiatric medications," Kawakami said. 

The findings of the study appear in the journal Current Biology.