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Scientists have captured stunning footage of neurons firing in the brain of a baby zebrafish as it swims.

A new technique, called light-sheet imaging, was able to capture 80 per cent of the fish's neurons in action, showing the electrical storm within its brain in unprecedented detail.

The study could allow researchers to better understand the 'rules' of the brain activity by mapping exactly which neurons are responsible for certain movements.

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In this image neurons in a zebrafish brain are coloured by the direction of motion they are associated. Red and pink respond to a backwards movement, bluish colours show forward progress. White neurons respond to every direction and black respond to none

'There must be fundamental principles about how large populations of neurons represent information and guide behaviour,' Jeremy Freeman of Howard Hughes Medical Institute in Virginia told Joshua Batson at Wired.

'In this system where we record from the whole brain, we might start to understand what those rules are.'

Professor Freeman and his team were able to use light-sheet imaging to capture the activity of about 80,000 neurons in the brains of zebrafish larvae.

Incredible video shows neurons firing in a zebrafish brain

The technique generates about a terabyte of data in an hour – presenting a data analysis challenge that helped motivate the development of new software called Thunder (pictured). The software created graphs that represents the activity of the whole brain during a single movement

Each zebrafish was genetically engineered to have a chemical indicator in each neuron. This indicators became fluorescent in the tenth of a second after a neuron fired.

In a light sheet microscope, a sheet of laser light scans across a sample, illuminating a thin section at a time.

To enable a fish in the microscope to see and respond to its virtual-reality environment, Professor Ahrens' team needed to protect its eyes.

So they programmed the laser to quickly shut off when its light sheet approaches the eye and restart once the area is cleared.

Then they introduced a second laser that scans the sample from a different angle to ensure that the region of the brain behind the eyes is imaged.

Together, the two lasers image the brain with nearly complete coverage without interfering with the animal's vision.

Professor Freeman and his team were able to use light-sheet imaging to capture the activity of about 80,000 neurons in the brains of zebrafish larvae

Each zebrafish was genetically engineered to have a chemical indicator in each neuron. This indicator becomes fluorescent in the tenth of a second after a neuron fired

Combining these two technologies lets researchers monitor activity throughout the brain as a fish adjusts its behaviour based on the sensory information it receives.

The technique generates about a terabyte of data in an hour – presenting a data analysis challenge that helped motivate the development of new software called Thunder.

When the scientists applied their new tools to the data, patterns quickly emerged.

At the beginning of the footage, the fish is resting and the forebrain region on the far-right is flashing.

Scientists then created the illusion that the fish was moving backwards by sliding bars in front of its eyes.

This caused a few neurons sitting just behind the eyes to light up followed by a huge amount of activity, including massive pulses caused by its intent to swim.

Every frame of the footage shows a half-second snapshot of the brain's activity.

The colours of the neurons indicate the direction of motion they best respond to. Red is linked too perceived backwards movement and bluish colours to moving forward.

White neurons respond to every direction and black respond to none. Purple and green regions in the middle light up when sideways sliding is detected.

In the forebrain, where thoughts and memories occur, the meaning of the colours is still unknown. 

The researchers used a 'Thunder' software to find patterns in high-resolution images collected from the brains of active zebrafish.

The team now plans to explore more complex questions using the new technology.

'At every level, this is really just the beginning,' said Professor Freeman.