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Scientists observe fish ‘thinking’ via brain imaging

Researchers involved in a new study have successfully imaged the brain of fish while watching its prey. The study, which is the first of its kind, was able to utilize the neural signals of a zebrafish larva to take a picture of the fish’s brain activity while stalking prey.

In order to see the neural signals of the zebrafish when taking the picture, scientists created a sensitive fluorescent marker that lit up the pathways. Those involved in the study hope that it will give them some insight into how the fish brain perceives that world around it.

Molecular and cell biologists Florian Engert, who works at Harvard University and was not involved in the study, believes the zebrafish brain image is a “breakthrough.” “No one else can look at neuronal activity with fluorescence microscopy in a freely swimming zebrafish larva” with such good resolution,” he told LiveScience.

The development and genetics of the zebrafish have been studying extensively by scientists. The larvae are of particular interest because of their see through heads, which allows researchers to literally seen into their brains.

Despite being able to peer into the minds of the zebrafish larvae, the research team wanted to see what was happening at the cellular level. In order to do this, they created a protein named GCaMP7a, which illuminates under a fluorescent microscope when the animal’s neurons signal to neighboring cells. The scientists bred zebrafish that expressed the protein in the optic tectum, a region of the brain that controls eye movement when the larva sees something move around it.

The scientists tested their fluorescent protein during a number of experiments. First, they took images of the zebrafish larva’s brain as a dot flashed on screen. The researcher made the dot move in different patterns, such as blinking on and off or moving back and forth. When the researchers looked at the animal’s brain images, its neurons fired in a pattern that mirrored the movement of the dot.

For the next experiment, the scientists introduced a live paramecium, which is a prey of the zebrafish, but held the animal still. They once again saw that the fish’s neurons fired in a pattern following the prey’s movement. Interestingly, when the paramecium was also immobilized, no neural signals were detected in the zebrafish larva’s brain.

Finally, the researchers allowed the zebrafish to chase after the paramecium. They continued to monitor the fish’s brain signals as it hunted its prey.

Zebrafish imaging is not a new area of interest for scientists. In fact single-cell brain activity in the animals has previously been imaged. However, the new study is the first to take a picture of the zebrafish’s neural signals as it swam freely towards prey. Joseph Fetcho, who has worked on zebrafish imaging, but was not part of this study, told LiveScience that “the technology for studying zebrafish is moving fast.”