Scientists for the first time have created computer reconstruction of a piece of neocortex. Supercomputers are used to create the simulation of the electrical behavior of the virtual brain tissue, and this provided key insights into the functioning of the neocortex. Now the breakthrough can help in a complete reconstruction and simulation of the brain.
The neocortical microcircuitry of the rat brain has been reconstructed by the Blue Brain Project. The virtual brain is characterized by about 30,000 neurons connected by 40 million synapses. The research is backed by a number of previous observations from the brain experiments, including tens of thousands of experiments performed on neurons and synapses in the neocortex of the young rats. Simulations revealed a series of fundamental rules that describe how neurons are arranged in the microcircuit and connected through synapses.
Michael Reimann, developed that algorithm to predict the locations of the synapses, and the lead author of the study said, “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.”
The simulations led to a number of new revelations about the brain. For instance, a simulation that looked at how different neurons respond to when the fibers coming into the neocortex is simulated by incoming fibers like a touch to the skin, the responses of the different types of neurons were consistent with what has been in previous studies. Further simulations revealed that the new information that exquisitely times sequences of activity (triplets) only occur when the circuit is in a very special state of activity. Another finding revealed the key role calcium plays in bran function. In the earlier simulation the burst of activity in sleeping animals are different from observed in awake animals.
Eilif Muller, lead author of the study said, “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.”
According to the research, 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.
Henry Markram said, “The reconstruction is a first draft, it is not complete and it is not yet a perfect digital replica of the biological tissue. 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 of the study were published in the journal Cell.