Ten Billion Relays

The more neurologists learn about the human brain, the more it looks like an electrical calculating machine. And the more engineers learn about an artificial calculating device, the more it resembles the human brain. Last week, Neurophysiologist Warren McCulloch of the University of Illinois tried to describe the brain in purely electrical terms to a New York meeting of the American Institute of Electrical Engineers.

The brain, said Professor McCulloch, is made up of neurons (nerve cells) which are nothing more nor less than small electrical relays, each containing its own built-in power supply. The cells burn sugar to carbon dioxide and water, and use the energy produced to keep their outer surfaces electrically charged in relation to their interiors. The electrical tension (voltage) between the two parts is about seven-hundredths of a volt.

Like a Radio. The nerve cells are laced together, like the vacuum tubes inside a radio, by slender, wirelike fibers (neurofibrils). Some cells have only two fibers; others have several hundred. Like the cells, the fibers are electrically charged.

In its normal state, a nerve cell is like an electrical relay waiting for a signal to send it into action. When the signal (a pulse of energy from another neuron) arrives, the cell "fires." An electrical disturbance starts at its center and travels outward along all its fibers. When the pulse reaches the end of a fiber and touches a fiber of another cell, it may or may not "fire" that cell, too. This selective action is the basis of the brain's operation.

Measured in electrical engineering terms, the neurons are only one-thousandth as fast as vacuum tube relays, but they require much less space and much less power. Professor McCulloch estimated that if a calculating machine had only 10 million vacuum tubes (the brain has about 10 billion neurons), it would take the power of Niagara Falls to operate it and the Niagara River to keep it from overheating. The brain is cooled by a comparatively small river of blood. When awake and in full operation, it raises the temperature of a pint of circulating blood one-half degree a minute.

Like a Flatworm. Calculating machines have been getting better and more complicated, Professor McCulloch told the engineers, but they have a long way to go before they rival the brain. A big calculator with 10,000 vacuum tubes may be a useful machine, but it has no more "intelligence" than a primitive flatworm with about that number of nerve cells. Lecturer McCulloch frankly admits that he cannot explain, in terms of electrical engineering, the brain's creative powers.

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