The Holy Grail of neuroscience is a complete map of all of the synaptic connections in your brain — which could allow us to describe the very flow of information in the brain.
And now, researchers working at the Blue Brain Project have successfully reconstructed a virtual microcircuit that is making it possible to predict the locations of synapses in the neocortex. This breakthrough could dramatically accelerate the brain-mapping project — while adding further credence to the suggestion that a simulated brain may someday be possible.
The Blue Brain Project was founded in 2005 by the Brain and Mind Institute of the École Polytechnique Fédérale de Lausanne in Switzerland. Their goal is to create a synthetic brain by reverse-engineering the mammalian brain down to the molecular level. To do so, they're using a Blue Gene supercomputer that runs NEURON software — a configuration that has resulted in a biologically realistic model of neurons.
Prior to their work, the Blue Brain researchers, a team led by Henry Markram, were not sure if mammalian neurons grew independently (just taking what they get as their branches bump into each other), or if the branches of each neuron were guided to its targets (such as chemical signaling). This presented a significant problem: The researchers were unable to work out how to connect neurons in their model — they didn't have a general rule to account for thousands or millions of connections.
To figure out what's going on, the researchers took real cells, injected them with a dye, and drew them in 3D. They did this for many cells, thus constructing numerous model neurons. For a second data set, they took two cells, injected them with dyes, and traced their branches to see where the synapses were formed.
What they discovered was that their model was very closely approximating that of real life — the locations matched that of synapses found in real brains with an accuracy ranging from 75% to 95%.
What this told the researchers was that the neurons do in fact grow independently of each other and that they tend to form synapses in locations where they randomly bump into each other. In other words, the system is much more simpler than they had realized, what Markram called a "remarkable design principle." As a result, the Blue Brain team can now develop highly accurate simulations in which synapses are correctly located inside the circuit.
The discovery also explains the associative nature of the human brain and why it's so resistant to damage. Their research suggests that the positions of synapses in the brain of all humans are more or less similar, and that this robust configuration is immune to changes in density, position, and orientation. The human brain can lose a lot of neurons, but that's not going to change the statistical locations of synapses.
Looking to the future, the discovery is set to significantly accelerate the rate at which the researchers can construct detailed models of the nervous system.
The paper will appear later this week in PNAS; we'll be sure to update this page once it has been posted.
Images via Blue Brain Project.