For the first time, researchers have been able to observe the thoughts of a living fish while it engages in its natural behavior.
The results could be useful in future studies of perception, and could even help the development of new psychiatric drugs.
"Our work is the first to show brain activities in real time in an intact animal during that animal's natural behavior," says Koichi Kawakami of Japan's National Institute of Genetics. "We can make the invisible visible; that's what is most important."
The team developed a very sensitive fluorescent probe to detect neuronal activity, along with a genetic method for inserting the probe directly into the neurons of interest. This allowed the researchers to detect neuronal activity atsingle-cell resolution in the zebrafish brain.
They observed what happens when a zebrafish sees something good to eat - in this case a swimming paramecium - and were able to correlate brain activity with the capture of the prey.
The new tool makes it possible to ask which brain circuits are involved in complex behaviors, from perception to movement to decision making, the researchers say, given that that the basic design and function of a zebrafish brain is very much like our own.
"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," says Kawakami.
He believes that researchers may in future be able 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," he says.