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180 mph

January 11, 2010

[Discover] The notion that the speed of thought could be measured, just like the density of a rock, was shocking. Yet that is exactly what scientists did. In 1850 German physiologist Hermann von Helmholtz attached wires to a frog’s leg muscle so that when the muscle contracted it broke a circuit. He found that it took a tenth of a second for a signal to travel down the nerve to the muscle. In another experiment he applied a mild shock to people’s skin and had them gesture as soon as they felt it. It took time for signals to travel down human nerves, too. In fact, Helmholtz discovered it took longer for people to respond to a shock in the toe than to one at the base of the spine because the path to the brain was longer.

Helmholtz’s results clashed with people’s gut instinct that they experienced the world as it happened, with no lag between sensation and awareness. “This is altogether a delusion,” German physiologist Emil Du Bois-Reymond declared in 1868. “It appears that ‘quick as thought’ is, after all, not so very quick.”

With their simple tools, Helmholtz and others could manage only crude measures of the speed of thought. Some of them came up with rates that were twice as fast as others. Researchers have been trying to get more precise results ever since. Today it is clear why they have had such a hard time. Our nerves operate at many different speeds, reflecting the biological challenges of wiring all the parts of the body together. In some ways evolution has fine-tuned our brains to run like a digital superhighway, but in other ways it has left us with a Pony Express. (read)

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