A remarkable multicoloured map of the brain that resembles an abstract painting has been created using a new method for staining nerve cells.

The “brainbow” technique developed by American scientists shows in unprecedented detail how parts of the brain interact and mature, promising fresh insights into the processes of thought.

It has already been used to analyse the brains of mice, allowing the researchers at Harvard University to chart how neurons are arranged and how different circuits relate to one another.

Although it will not be possible to create brainbow maps for people, because the method involves genetic modification, its use on other laboratory mammals is expected to shed light on the development of the brain and the processes that trigger diseases such as Parkinson’s and Alzheimer’s.

Scientists have been staining nerve cells for more than a century, since Santiago Ramón y Cajal, a Spanish neuroscientist, pioneered the application of a method called Golgi staining.

This method opened the door to modern neuroscience, by allowing scientists to study brain structure, but until now it has proved impossible to map individual neurons and brain circuits in more detail.

The brainbow technique enables researchers to label individual neurons with about 90 colours: previous methods could cope with no more than a handful. Details are published today in the journal Nature.

Mice are first genetically modified so that they carry genes that express fluorescent proteins that glow green, yellow, orange or red. These genes originate from other organisms: the green protein, for example, comes from a jellyfish, and is widely used as a marker in genetic engineering experiments.

The team, led by Professor Jeff Lichtman and Professor Joshua Sanes, then used a recombination method known as Cre-lox to shuffle the genes.

The result is that each nerve cell expresses a random combination of the four proteins, producing a characteristic colour. With about 90 discernible hues, it is then possible to track that cell’s development, and when it is firing as part of a brain circuit.

“In the same way that a television monitor mixes red, green and blue to depict a wide array of colours, the combination of three or more fluorescent proteins in neurons can generate many different hues,” Professor Lichtman said.

“There are few tools neuroscientists can use to tease out the wiring diagram of the nervous system. Brainbow should help us much better to map out the brain and nervous system’s complex tangle of neurons.”

Jean Livet, another member of the Harvard team, said: “The technique drives the cell to switch on fluorescent protein genes in neurons, more or less at random. You can think of brainbow almost like a slot machine in its generation of random outcomes, and Cre-lox is the hand pulling the lever over and over again.”

Professor Sanes said that the method had already allowed the team to examine how a mouse brain was organised.

“We’ve observed some very interesting, and previously unrecognised, patterns of neuron arrangement,” he said. “As far as understanding what we’ re seeing, we’ve only just scratched the surface.”

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