Defending free will: A fruit fly makes choices

Wed May 16, 2007 1:37AM EDT
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By Julie Steenhuysen

CHICAGO (Reuters) - A tiny fruit fly -- without any input from the outside world -- will spontaneously change directions, researchers said on Monday in a finding that just may rescue the notion that free will not only exists but is a basic function of the brain.

"Neuroscientists have been claiming free will doesn't exist," said Bjorn Brembs, a neurobiologist of the Free University Berlin in Germany who led the study.

The claim is based on work in the 1980s by neuroscientist Benjamin Libet of University of California San Francisco, who discovered that even before a person made a conscious decision to move, the brain had already started the process of movement.

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Neuroscientists say this so-called "readiness potential" suggests that the brain simply responds to outside stimuli, and consciousness is just the brain's way of rationalizing actions the brain has already determined to take.

"There are many prominent people who claim the main function of the brain is to compute input to output," Brembs said in a telephone interview.


But what if there was no input, Brembs wondered.

He and colleagues devised an experiment with fruit flies in which they were deprived of all external stimuli.

Animals, and particularly insects, are often seen as complex robots, responding only to external stimuli, said Brembs, whose work appears in the Public Library of Science journal PLoS One.

The researchers placed a single fruit fly in a pure white chamber -- devoid of visual cues. The fly was fixed in place and its attempts to turn were recorded. Researchers repeated their experiment on many flies and analyzed the data using a series of complex mathematical models.

What they found was surprising.

Lacking external input, Brembs said he had expected a pattern of entirely random movement or noise -- akin to static on a radio that is tuned between stations. Instead, the flies showed a pattern of flight that was generated spontaneously by the brain and could not have been random.

"The decision for the fly to turn left or turn right, which it changes all the time, has to come from the design of the brain," Brembs said.

Brembs said the finding reveals a mechanism that could form the biological basis of free will.

"I don't think we've found consciousness in the fruit fly," he said. "It's like one of the first building blocks, without which you can't go on."

George Sugihara, a mathematical biologist at the Scripps Institution of Oceanography at the University of California San Diego who helped with the data analysis, said the pattern of variability shown by the fly's choices revealed a non-linear signature -- something typical of many biological processes.

"We show free will 'can' exist, but we do not 'prove' it does," Sugihara said.

"Our results eliminate two alternative explanations of this spontaneous turning behavior that would run counter to free will, namely randomness and pure determinism," he said in an e-mail.

He said the results address the middle ground between simple determinism -- the brain as an input-output machine -- and utterly random behavior.

"We speculate that if free will exists, it is in this middle ground," he said.

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