Lost fish find their way home thanks to this

By Mark Waghorn via SWNS

Lost fish find their way home thanks to how their brains are wired, according to new research.

The neuronal circuit evolved up to half a billion years ago - and could have been passed onto humans.

It enables our slippery ancestors to get back on course - even after being swept away by fast-flowing currents.

The discovery sheds fresh light on the workings of the ancient brain and may apply to other vertebrates - including us.

There are potential implications for treating Alzheimer's. Patients frequently lose their way in familiar as well as unfamiliar surroundings - even in the early stages.

Co-author Dr. Misha Ahrens, of Howard Hughes Medical Institute, Chevy Chase, Maryland, said: "This is a very unknown circuit for this form of navigation.

"We think it might underlie higher order hippocampal circuits for exploration and landmark-based navigation."

The study in Cell is based on the humble zebrafish - long used in medical research as a model for human health.

It found the key chemical pathways cross different regions at the back of the brain - helping the lost fish regain their bearings.

In experiments, the tiny translucent fish traversed a 2D virtual reality environment in the presence of a simulated flow.

As they swam toward a target strong water unexpectedly pushed them off course. They still swam back to where they started, determined to finish the journey.

Scans showed the hindbrain - a conserved area at the rear - computes their spot. They use the information to figure out where to go next.

First author Dr. En Yang and colleagues used a 'whole imaging' technique developed at their lab to measure what is happening.

It allowed scientists to search the fish's entire brain to see which circuits are activated during course-correcting - and disentangle the individual components involved.

They expected to see cells triggered in the forebrain where the hippocampus, which contains a 'cognitive map' of an animal’s environment, is located.

To their surprise, they saw activation in several regions of the medulla. Information was being transmitted from a newly identified circuit.

It passed through a hindbrain structure called the inferior olive to the motor circuits in the cerebellum that enable the fish to move.

When these pathways were blocked, fish were unable to navigate back to their original location.

The findings suggest areas of the brainstem remember a zebrafish’s original location and generate an error signal based on its current and past locations.

This is relayed to the cerebellum - allowing the fish to swim back to its starting point. It reveals a new function for the inferior olive and the cerebellum.

They were known to be involved in actions like reaching and locomotion, but not this type of navigation.

Dr. Yang said: "We found the fish is trying to calculate the difference between its current location and its preferred location and uses this difference to generate an error signal.

"The brain sends that error signal to its motor control centers so the fish can correct after being moved by flow unintentionally, even many seconds later."

It is still unclear whether these same networks are involved in similar behavior in other animals.

But the researchers hope labs studying mammals will now start looking at the hindbrain for homologous circuits for navigation.

This hindbrain network could also be the basis of other navigational skills, such as when a fish swims to a specific place for shelter, Dr. Ahrens added.

Zebrafish are colorful creatures, named after their stripes. They are popular additions to aquariums due to their social, peaceful nature.

But they can be aggressive if housed in a crowded tank. Humans and all other vertebrates evolved from fish.

Conventional wisdom is fish shimmied landwards roughly 370 million years ago as primitive, lizard-like animals known as tetrapods.