Lost fish find their way, thanks to their ‘an

Zebrafish swim towards their intended target but are thrown off course by strong currents. Nevertheless, the little fish decided to swim back to where it came from and complete its journey.

How do animals know where they are in their environment, and how does that determine subsequent choices? evolutionarily conserved or “ancient” regions) help animals calculate their position and use that information to determine where they need to go next. .

of new researchpublished in magazines cell December 22nd, It reveals some new functions of the ‘ancient brain’ and may apply to other vertebrates.

Whole-brain imaging reveals new networks

To elucidate how animals understand their position in the environment, researchers Ahrens Labplaces a small translucent zebrafish, just 0.5 centimeters long, in a virtual reality environment that simulates water flow. An unexpected change in current will initially throw the fish off course. However, you can correct that movement and return to where you came from.

While the zebrafish swims in a virtual reality environment, researchers use a whole-brain imaging technique developed at Janelia to measure what is happening in the fish’s brain. This technique allows scientists to search the entire brain to find out which circuits are activated during course-correcting behavior and disentangle the individual components involved.

Researchers expected to see activation in the forebrain, where the hippocampus is located, which contains a “cognitive map” of the animal’s environment. Surprisingly, activation was seen in several regions of the medulla. There, information about the animal’s position was transmitted from a newly identified circuit, through a hindbrain structure called the inferior olive, to motor circuits in the cerebellum that enable fish movement. Once these pathways were blocked, the fish were unable to return to their original location.

These findings suggest that regions of the brainstem remember their original positions in zebrafish and generate error signals based on current and past positions. This information is relayed to the cerebellum, allowing the fish to swim back to its starting point. This study reveals novel functions in the inferior olive and cerebellum known to be involved in behaviors such as reaching and locomotion, but not in this type of navigation.

“We found that fish are trying to calculate the difference between their current position and their preferred position, and use this difference to generate an error signal,” said Yang, the first author of the new study. say. “The brain sends that error signal to the motor control center, allowing it to correct itself even seconds after the fish has been unintentionally moved by the current.”

A novel multiregional hindbrain circuit

It is still unclear whether these same networks are involved in similar behaviors in other animals. I hope to start paying attention to the brain.

This hindbrain network may also underlie other navigational skills, such as when fish swim to a specific location as a refuge, the researchers say.

“This is a highly unknown circuit of this form of navigation that is thought to underlie the higher-order hippocampal circuit for exploration and landmark-based navigation,” says Janelia senior group leader Misha Ahrens.