An international team of scientists has discovered that the human brain, the nervous system of a worm and a computer chip are strikingly similar. The research may help to explain the relationship between the processing elements (or gray matter) and the wiring (the white matter) in the brains of a wide range of mammals. Moreover, it appears that in the case of the brain and a computer chip - evolution and technological innovation have developed the same solutions to optimal mapping patterns.
The scientists working on the project came from the U.S., the U.K. and Germany. They discovered that there are novel quantitative organizational principles that are similar in the network organizations of the human brain, the nervous system of a worm (nematode C. elegans) and high-performance computer chips. In order to understand how the elements in each system were networked, they mostly used data that is commonly available in the public domain - including a map of nematode's nervous system, a standard computer chip and magnetic resonance imaging data from human brains.
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The surprising discovery was that they all shared two common properties. Firstly, all three have an architecture described as Russian doll-like with the same patterns repeating over-and-over again at different scales. Secondly, they all showed evidence of Rent’s scaling which is a rule that describes the relationship between the number of elements in a given area and the number of links between them.
Danielle Bassett, first author and a postdoctoral research associate in the Department of Physics at UC Santa Barbara, said, "Brains are often compared to computers, but apart from the trivial fact that both process information using a complex pattern of connections in a physical space, it has been unclear whether this is more than just a metaphor."
Bassett explained that although worm brains seem dissimilar to human brains and quite different to computer circuits, they all contain a pattern of connections that are locked together in one physical space. She likened this to the way tracks in a railway are locked together solidly to the ground with traffic paths that have fixed GPS coordinates.
Initially, a computer chip has an abstract connectivity pattern designed to perform a specific function. It then maps this connectivity pattern on to the chip surface which is two-dimensional. The mapping must be done carefully to maximize the total length of the wires which indicates the cost of manufacturing a chip whilst still maintaining the abstract function. The human brain is surprisingly similar.
"Brains are similarly characterized by a precise connectivity which allows the organism to function, but are constrained by the metabolic costs associated with the development and maintenance of long 'wires,' or neurons," said Bassett. While the constraints suggest that evolution and technological innovation have arrived at the same solution for optimizing mapping patterns, Bassett also explained that the scaling result might explain the relationship between the processing elements (neuronal cell bodies, or gray matter) and wiring (axons, or white matter) in the brains of a wide range of differently sized mammals. This might mean that, across species - the principles of nervous system design are highly conserved.
In addition, both the brain and the computer chip’s information processing network suggest that technological innovation and evolution have negotiated “trade-offs” between cost and complexity.
Edward Bullmore, professor of psychiatry at the University of Cambridge who worked closely with Bassett, explained it better, "These striking similarities can probably be explained because they represent the most efficient way of wiring a complex network in a confined physical space –– be that a three-dimensional human brain or a two-dimensional computer chip."