Mapping the changing gaze of the “fishers”.

Zebrafish is one scientific underfish. They have Werewolf-like regeneration ability-and can almost completely regrow his spinal cord after injury. They also give researchers insight into some of them the most primal state of the animal brain. When a team of researchers worked with week-old zebrafish larvae, they decoded how they connect as one network of neurons in the brainstem’s guide where the fish look. They also created a simplified artificial circuit that can predict visual movements and activity in the animal’s brain. This discovery sheds light on how the brain manages short-term memory and could lead to some new ways to treat eye movement disorders in humans. The results are described in detail in a study published November 22 in the journal Nature Neuroscience. It also comes with a striking image taken with a microscope, with vivid colors that show off the brain regions that control eye movements.

Shifting eyes and altered brain states

Animal brains are constantly taking in a variety of sensory information about the environment, even when we don’t consciously realize it. This data often changes from one moment to the next and the brain is faced with the challenge of retaining these quick, small nuggets of information long enough to make sense out of them. For example, it must connect what a set of mysterious sounds might be or allow an animal keep your eyes focused on an area of interest as prey or a potential threat lurking in the distance.

“Trying to understand how these short-term memory behaviors are generated at the level of neural mechanisms is the core goal of the project,” study co-author and Weill Cornell Medicine physiologist Emre Aksay said in a statement.

(Family: How animals see the world, according to a new camera system.)

To decode the behavior that goes on in these dynamic brain circuits, neuroscientists build mathematical models which describes how the state of a system changes over time and where the current state determines the future state of the circuit according to a set of rules. One of the brain’s short-term memory circuits will remain in a single preferred state, only until a new stimulus arrives. When the new stimulus appears, the circuit will settle into a new state of activity. In the visual-motor system, each of these states can store the memory of exactly where an animal should look.

However, questions remain about rules and parameters that help set up that type of switching system. An opportunity is about circuit anatomy– the connections formed between each neuron and how many connections they form. A second possibility is the physiological strength of these connections. This strength is determined by several factors, including the amount of a neurotransmitter that is released, the type of receptors that capture the neurotransmitters, and the concentration of those receptors.

Building a neural circuit from scratch

In this new studythe team sought to understand what contributions the circuit’s anatomy made to the visual system. At just five days old, zebra “fish” are already swimming around hunting prey. Looking for something to eat involves sustained visual attention and the brain region that controls eye movements is structurally similar in both fish and mammals. However, the zebrafish system contains only 500 neurons. In comparison, the human brain has approximately 100 billion neurons.

“So we can analyze the whole circuit — microscopically and functionally,” Aksay said. “It’s very difficult to do in other vertebrates.”

(Family: Why are we sending so many fish into space?)

At the same time, the team uses several advanced imaging techniques identified the neurons involved in controlling zebrafish gaze and how all these neurons are connected. They found that the system consists of two prominent feedback loops. Each of these feedback loops contains three clusters of closely connected cells. Using this set-up, they developed a computer model of what happens in this part of the zebrafish’s brain.

When the team compared the artificial network they built with physiological data from a real zebrafish, they found that their fake network could accurately predict the activity patterns.

“I consider myself a physiologist, first and foremost,” Aksay said. “So I was surprised at how much of the circuit’s behavior we could predict just from the anatomical architecture.”

(Family: Scientists mapped every neuron in an adult animal’s brain for the first time.)

Future applications

In future studiesthe team plans to explore how the cells in each cluster contribute to the circuit’s behavior and whether the neurons in the different clusters have specific genetic signatures. This type of data could help doctors therapeutically target cells that may be faulty in humans disturbances in eye movements. Strabismus occurs when both eyes are not aligned in the same direction and results in “crossed eyes” or “grass”. The disorder nystagmus appears as rapid, uncontrollable eye movements, sometimes called “dancing eyes”.

The findings also give researchers a way to unravel the more complex computational systems in the brain that depend on it short term memory, such as those who understand speech or decipher pictures.