Scientists have created the world's first draft computer reconstruction of a piece of the neocortex. The incredible simulation of the electrical behavior of the virtual brain tissue was created using supercomputers, and provided key insights into the functioning of the neocortex, EPFL reported. The breakthrough could lead to a complete digital reconstruction and simulation of the brain.
The Blue Brain Project created a reconstruction of the neocortical microcircuitry of a rat brain, which is characterized by about 30,000 neurons connected by 40 million synapses. The findings backed up a number of previous observations taken from brain experiments, validating the accuracy of this type of research. The research involved tens of thousands of experiments performed on neurons and synapses in the neocortex of young rats. The simulations revealed a series of "fundamental rules" that describe how the neurons are arranged in the microcircuit and connected through synapses.
"The algorithm begins by positioning realistic 3D models of neurons in a virtual volume, respecting the measured distribution of different neuron types at different depths. It then detects all locations where the branches of the neurons touch each other - over 600 million. It then systematically prunes all the touches that do not fit with five biological rules of connectivity. That leaves 37 million touches. These are the locations where we constructed our model synapses," said Michael Reimann, a lead author who developed the algorithm used to predict the locations of the synapses.
The simulations led to a number of new revelations about the brain. For example, a simulation that looked at how different neurons respond to when the fibers coming into the neocortex is stimulated by incoming fibers (such as a touch to the skin), the responses of the different types of neurons were consistent with what has been seen in previous studies. Further simulations revealed the new information that exquisitely timed sequences of activity (triplets) only occur when the circuit is in a "very special" state of activity. Another unexpected finding revealed key roles calcium plays in brain function. Earlier simulations had shown bursts of activity in sleeping animals was much different from what was observed in awake animals.
"When we decreased the calcium levels to match those found in awake animals and introduced the effect that this has on the synapses, the circuit behaved asynchronously, like neural circuits in awake animals," said Eilif Muller, a lead author of the study.
The research suggest that there are many cellular and synaptic mechanisms that have the ability to shift the circuit from one state of activity to another, and that circuit can change its state to allow for different computing capabilities. If this is true, it could lead to new ways of studying information processing and memory mechanisms in normal brain states such as wakefulness and sleep.
"The reconstruction is a first draft, it is not complete and it is not yet a perfect digital replica of the biological tissue," said Henry Markram. "The job of reconstructing and simulating the brain is a large-scale collaborative one, and the work has only just begun. The Human Brain Project represents the kind of collaboration that is required."
The findings were published in a recent edition of the journal Cell.
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