Of Brains, Worms and Chips
The brain, in some ways, is simply the biological device that keeps a body running and the mind thinking. In that way it is like a computer. An international team of scientists has discovered striking similarities between the human brain, the nervous system of a worm, and a computer chip. The finding is reported in the journal PloS Computational Biology today.
The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all.
Brains can be extremely complex. The cerebral cortex of the human brain contains roughly 15—33 billion neurons, perhaps more, depending on gender and age, linked with up to 10,000 synaptic connections each. Each cubic millimeter of cerebral cortex contains roughly one billion synapses.
In computers, an integrated circuit (also known as IC, microcircuit, microchip (chip), silicon chip, or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material. They are the base of modern computer design and function.
A computer chip starts out as an abstract connectivity pattern, which can perform a specific function. Further design involves mapping that connectivity pattern onto the two dimensional surface of the chip.
"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," said Danielle Bassett, first author and a postdoctoral research associate in the Department of Physics at UC Santa Barbara.
The team of scientists from the U.S., the U.K., and Germany has uncovered novel quantitative organizational principles that underlie the network organizations of the human brain, high performance computer circuits, and the nervous system of the worm. Using data that is largely in the public domain, including magnetic resonance imaging data from human brains, a map of the nematode's nervous system, and a standard computer chip, they examined how the elements in each system are networked together.
They found that all three shared two basic properties. First, the human brain, the nematode's nervous system, and the computer chip all have a Russian doll-like architecture, with the same patterns repeating over and over again at different scales.
Second, all three showed what is known as Rent's scaling, a rule used to describe the relationship between the number of elements in a given area and the number of links between them.
It is odd to compare worm brains to human brains. However. what this shows is that the same principle of organization applies to both man as well as a worm and presumably applies to other types of biological brains.
In fact, each of these systems contains a pattern of connections that are locked solidly in a physical space, similar to how the tracks in a railway system are locked solidly to the ground, forming traffic paths that have fixed coordinates.
"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. She explained that, given the similar constraints in brains and chips, it seems that both evolution and technological innovation have developed the same solutions to optimal mapping/organizational patterns.
She explained that this scaling result may further explain a well known but little understood 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 —— from mouse to opossum to sea lion.
This work suggests that the market instigated design and development of computers and natural biological selection have found the same trade offs between cost and complexity in designing both types of information processing network: brains and computer circuits.
For further information: http://www.eurekalert.org/pub_releases/2010-04/uoc--bwa042210.php