Brain of fish found the center of social behavior

(ORDO NEWS) — Scientists showed Danio rerio aquarium fish fry dots on a screen that move in the same way as the animals themselves.

This led to the activation of neurons in a specific part of the fish thalamus, which play a key role in recognizing relatives and seeking company.

Many animals live among their own kind, that is, representatives of the same species. Some of them can be called eusocial , since they are engaged in joint purposeful activities and do not survive individually, some are gregarious, because they huddle in huge hordes or shoals for common feeding.

Many mammals and birds live in a group of constantly interacting individuals – these are packs of wolves, and prides of lions, and bird colonies.

As if some kind of physical force makes the animals reach out to each other – and remain in the company of “their own”.

The authors of a new study, published in the leading scientific journal Nature , set out to address the biological basis of this “social attraction” and examine the part of the fish brain that makes them social.

To form a group, animals first need to recognize relatives. As a rule, this happens intuitively and extremely quickly. At the same time, it turned out to be by no means easy to find the corresponding center in the brain.

“The study of social interactions inevitably encounters certain difficulties. For us, observers, such actions and reactions are always mixed – both at the level of animal behavior and at the level of organization of nerve cells, – explained Johannes Larsch, one of the authors from the Max Planck Institute for Biological Intelligence (Germany).

The thing is that interacting individuals change each other’s behavior. They are both sources and receivers of the social signal.

It has been particularly difficult to explore the role that the visual system and associated brain regions play in this.”

The scientists sought to elucidate the neurophysiological basis of kin recognition using fish, or rather the standard workhorse of experimental biology, the Danio rerio , as an example.

The fry of this aquarium fish were placed in a kind of “virtual reality”, that is, a container with a screen on which dots appeared.

These points made sharp twitching movements – the same ones that are characteristic of the fry-observer himself.

As a result, he swam tirelessly for hours towards the moving spot – from his point of view, indistinguishable from his relative. It turns out that this simple and automatic reaction is “hardwired” in the small brain of fish.

What happens at the same time in the head of the Danio rerio fry ? Evaluation of brain activity showed that when a fish looks at the movement of a point, a specific group of thalamic neurons is activated.

This is an area responsible for the regulation of various physiological processes, processing signals from the sense organs and coordinating the work of other parts of the brain.

Exactly the same activation of special thalamic neurons occurs when a fry observes the movement of relatives.

It turns out that we have before us something that can be conditionally called the center of the social behavior of the brain of fish.

At the same time, a selected group of nerve cells serves as an intermediary connecting the visual system of the fish with other parts of the brain, which are also activated upon contact with representatives of the same species.

After that, the biologists turned off these neurons, observed the loss of the “social reflex” and thus confirmed their case.

“Before that, we knew that these other areas of the brain are involved in social interactions. However, details about the visual stimuli that trigger them were not known.

Our work filled this gap and made it possible to identify chains of neurons, in this case transmitting a signal, ”concluded Dr. Larsh.

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