On the one hand, this headgear looks like something a cyberfish would wear. On the other, it’s not far from a fashion statement someone at the Kentucky Derby might make.
But scientists didn’t just affix this device for laughs: They are 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 circuitry.
“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 a team that fitted 15 fish with cybernetic headgear for a study published on Tuesday in the journal PLOS Biology.
Putting a computer on a goldfish to study how the neurons fire in its brain while navigating wasn’t easy.
It takes a careful hand because a goldfish’s brain, which looks a bit like a small cluster of lentils, is only half an inch long. “Under a microscope, we exposed the brain and put the electrodes inside,” said Lear Cohen, a neuroscientist and doctoral candidate 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 test subject. “The fish needs water and you need him not to 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, which could monitor neuronal activity and which was sealed in a waterproof case, mounted on the fish’s forehead. To keep the computer from weighing the fish down and impeding its ability to swim, the researchers attached buoyant plastic foam to the device.
After recovering from surgery, the fish debuted their headgear in an experiment. The goldfish navigated a two-foot-long, six-inch-wide tank. The closer the fish swam to the tank’s edges, the more the navigational cells in their brains lit up.
The fish’s brain-computer helped reveal that goldfish use a system of navigation that is subtly different from what scientists have found in mammals. For humans (and other members of our class), navigational 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 didn’t find those cells in fish.
Instead, goldfish rely on a type of neuron that fires to let the animal know it is approaching a boundary or an obstacle. By combining the information about how far it is from various barriers, the fish is able to orient itself in space.
The mammalian navigation system, Dr. Segev said, amounts to cells that let an animal determine “I’m here, I’m here, I’m here.” In goldfish, he said, the cells work to impart a different message: “I’m in this position along this axis, and this position along a different axis.”
Mr. Cohen suspects that the variations in animals’ navigation circuits may correspond to the different challenges they face getting around their habitats. For instance, he said, the ever-shifting currents of a watery home could mean that, for fish, “it’s easier to know the distance from a salient feature in the environment than knowing an exact position.”
All of the experiments were approved by the university’s animal welfare committee and the researchers euthanized the fish after their swimming trials so they could further examine their brains. The team hopes to continue learning how and why fish’s navigational systems differ from ours.
Adelaide Sibeaux, a biologist at Oxford University who was not involved with the study, said she found the project “pretty amazing” as well as important.
“We’re modifying a lot of animals’ environments, and, if you understand how an animal navigates, you will know if they are able to cope with changes that are happening in the world at the moment,” Dr. Sibeaux said; for fish, that could include water that becomes murkier because of pollution.