On the one hand, this headgear looks like something a cyberfish would wear. Then again, it’s not a far cry from a fashion statement someone could make at the Kentucky Derby.
But scientists didn’t just put this device on for fun: They’re curious about the underlying brain mechanisms that allow fish to navigate their world, and how such mechanisms relate to the evolutionary roots of navigation for all creatures with brain circuits.
“Navigation is an extremely important aspect of behavior because we navigate to find food, to find shelter, to escape predators,” said Ronen Segev, a neuroscientist at Ben-Gurion University of the Negev in Israel, who was part of from a team that tested 15 fish wearing cybernetic headgear for a study published Tuesday in the journal PLOS Biology.
Putting a computer on a goldfish to study how the neurons fire in its brain as it navigates wasn’t easy.
You have to be careful, because the brain of a goldfish, which looks a bit like a small clump of lentils, is only an inch long. “Under a microscope, we exposed the brain and placed the electrodes inside,” said Lear Cohen, a neuroscientist and PhD student at Ben-Gurion who performed the surgeries to attach the devices. Each of those electrodes was the diameter of a strand of human hair.
It was also tricky to find a way to perform the procedure on dry land without harming the subject. “The fish needs water and you need it to not move,” he said. He and his colleagues solved both problems by pumping water and anesthetics into the fish’s mouth.
Once the electrodes were in the brain, they were connected to a small recording device that could monitor neuronal activity and was sealed in a waterproof case mounted on the fish’s forehead. To prevent the computer from weighing down the fish and hindering its ability to swim, the researchers attached floating plastic foam to the device.
After recovering from surgery, the fish debuted their headgear in an experiment. The goldfish navigated a tank 2 feet long and 6 inches wide. The closer the fish swam to the edge of the aquarium, the more the navigational cells in their brains lit up.
The fish’s brain computer helped reveal that goldfish use a navigational system subtly different from what scientists have found in mammals. For humans (and other members of our class), navigation cells specialize in pinging our precise location within our environment and building a map around that spot. Mammals have specialized neurons that create these “you are here” pins in their mental maps; the researchers did not find those cells in fish.
Instead, goldfish rely on a type of neuron that fires to let the animal know it’s approaching a boundary or obstacle. By combining the information about the distance to different barriers, the fish can orient itself in space.
The mammalian navigation system, said Dr. Segev, comes down to cells that allow an animal to say, “I’m here, I’m here, I’m here.” In goldfish, he said, the cells work to convey a different message: “I’m in this position along this axis and this position along another axis.”
Mr. Cohen suspects that the variations in animals’ navigational circuits may correspond to the different challenges they face moving around their habitats. For example, he said that the ever-changing currents of a wetland home could mean that it is “easier for fish to know the distance to a salient feature in the environment than to know an exact position.”
All the experiments were approved by the university’s animal welfare committee, and the researchers euthanized the fish after their swimming trials so they could study their brains further. The team hopes to continue learning how and why fish navigation systems differ from our own.
Adelaide Sibeaux, a biologist at the University of Oxford who was not involved in the study, said she found the project “pretty amazing” as well as important.
“We’re changing the environment of a lot of animals, and understanding how an animal navigates will tell you if they are able to cope with changes that are happening in the world right now,” said Dr. Sibeaux; for fish, that could be water that becomes cloudier due to pollution.
