Digital version of piece of rat brain fires like the real thing

The brain is going digital. A tiny piece of a rat’s brain has been reconstructed in minute detail in a computer. The digital piece of brain, which includes 31,000 neurons and their 37 million synapses, fires like the real thing, and is already revealing fresh clues as to how the brain works.

The simulation is the first significant achievement of the Blue Brain project, which was launched 10 years ago by Henry Markram at the Swiss Federal Institute of Technology in Lausanne, Switzerland. Today’s breakthrough represents the first step to a larger goal – creating a digital model of the entire human brain to probe consciousness itself.

So far, the digital brain recreates a piece of tissue about one third of a millimetre cubed. It contains 207 different types of brain cells and the millions of connections between them. The team hopes to use the virtual brain to perform experiments that would be impossible in real tissue.

“As one of the first concrete outputs from the billion-euro Human Brain Project this had to be a substantial piece of work, and it is,” says Anil Seth at the University of Sussex in the UK. “I am impressed by the simulation detail, and by the wealth of experimental data that is accounted for.”

Microcircuit brain

Markram and his many colleagues – a team comprising 82 people across 12 institutions – created their model using data they have been collecting for the last two decades. For 20 years, the teams have been pulling apart a tiny brain region that is responsible for a rat’s sensing of touch. This tiny area has been sliced, stained, dissected and stimulated every which way. “We’ve recorded and labelled 14,000 neurons,” says Markram.

Using this information, his team developed an algorithm to predict how the neurons connect with each other and fire together. After carefully creating digital reconstructions of about 1000 of their recorded neurons, the team applied their algorithm to recreate 31,000 neurons, all connected to each other.


Together, these neurons make up a microcircuit, says Markram – a miniature network of neurons that communicate with each other. “It’s the minimum size of a society of neurons,” says Markram.

The resulting model is the most detailed reconstruction of a brain to date. In July, a team at Harvard University built a 3D map of what they described as a “crumb” of mouse brain based on microscopic images of thousands of brain slices. The new model is around 100,000 times larger.

Choristers and soloists

Markram and his colleagues have already started putting their digital brain through its paces. When the group carefully stimulated their model, mimicking how the living version receives information from other parts of the brain, they found that it responded like the real thing. “The digital piece of tissue behaved very similarly to what we see in the brain,” says Markram. “We see the same patterns of firing, with the same delay.” The digital brain could also adopt different states of activity – representing a sleepy or alert rat.

The digital brain imitates a real brain in other ways, too. For example, the team was able to spot what neuroscientists call “choristers” and “soloists” – neurons that fire in groups and alone. They also spotted triplets – neurons that fire in three beats. “They go pop-pop-pop, like Morse code,” says Markram.

“Ultimately we want to understand the mechanisms behind cognition, and what makes us do what we do,” says Markram, who describes the model as a “first draft”.

When the Blue Brain project was launched, Markram’s aim to rebuild the human brain in digital form was met with some scepticism. And when Markram launched the 10-year European Human Brain Project a couple of years ago to support the venture, with expected costs running at 1.2 billion euros, neuroscientists around the world voiced concerns that the project was doomed to failure and a waste of money. “Ten years ago I made a promise [to create a digital representation of the brain], and now I’ve delivered on that promise,” says Markram.

Seth isn’t so sure that simulations will answer all of neuroscience’s big questions. “Let’s applaud this Herculean effort to simulate a tiny part of a tiny brain,” he says. “Only time will tell whether it will play a significant role in unravelling the properties of the most complex object in the known universe.”

Reference: Cell, DOI: 10.1016/j.cell.2015.09.029

Image credit: Makram et al./Cell 2015Makram et al./Cell 2015

By Jessica Hamzelou

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