On the one hand, this headgear looks like something a cyberfish would wear. On the other hand, it’s about as far from a fashion statement as someone at the Kentucky Derby might make.
But the scientists didn’t just post this contraption for fun: They were curious about the underlying brain mechanisms that allow fish to navigate their world, and how those mechanisms relate to the evolutionary roots of navigation in all organisms with brain circuits.
“Navigation is an extremely important aspect of behavior because we navigate to find food, to find shelter, to avoid predators,” says neuroscientist Ronen Segev of Ben-Gurion University of the Negev, Israel, and part of a team that The team equipped 15 with a study published Tuesday in the journal PLOS Biology.
Putting a computer on a goldfish to study how neurons in the brain fire while navigating isn’t easy.
This needs to be done carefully, as a goldfish’s brain looks a bit like a small cluster of lentils, only half an inch long. “Under the microscope, we exposed the brain and put electrodes in there,” said Lear Cohen, a neuroscientist and doctoral candidate at Ben-Gurion University, who performed the surgery to connect the device. Each of these electrodes is the diameter of a strand of human hair.
Finding a way to perform the procedure on land without harming test subjects is also tricky. “A fish needs water and you need it to not move,” he said. He and his colleagues solved both problems by pumping water and an anesthetic into the fish’s mouth.
Once the electrodes are in the brain, they are connected to a small recording device that monitors neuronal activity and are sealed in a waterproof case mounted on the fish’s forehead. To prevent 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 showed off their headgear for the first time in an experiment. The goldfish sailed in a tank that was two feet long and six inches wide. The closer the fish swam to the edge of the tank, the more active the navigation cells in their brains were.
The fish’s brain computer helped reveal that goldfish use a slightly different navigation system than scientists have found in mammals. For humans (and other members of our class), navigation cells are specialized in determining our precise location in the environment and drawing a map around that location. Mammals have specialized neurons that create these “you are here” pins in their mental maps; the researchers did not find these cells in fish.
Instead, goldfish rely on a type of neuron that lets the animal know it’s approaching a boundary or obstacle. By combining information about its distance from various obstacles, the fish is able to orient itself in space.
Dr. Segev said the mammalian navigation system amounts to cells that allow the animal to determine “I’m here, I’m here, I’m here.” In goldfish, he says, the cells send different messages: “I’m in this position on this axis, and this position is in another axis.”
Mr Cohen suspects that changes in the animals’ navigation circuits may correspond to the different challenges they face around their habitats. For example, he said, the changing currents of the water house might mean that, for fish, “it’s easier to know the distance to a salient feature in the environment than the exact location.”
All experiments were approved by the University Animal Welfare Committee, and the researchers euthanized the fish after the swim test for further examination of their brains. The team hopes to continue to understand how and why fish’s navigation systems differ from ours.
Adelaide Sibeaux, a biologist at the University of Oxford who was not involved in the study, said she found the project “remarkably remarkable” and important.
“We’re changing the environment for a lot of animals, and if you understand how animals navigate, you can tell if they’re able to cope with the changes that are happening in the world right now,” Dr Sibeaux said; more turbid water.