Studies now show that the conscious mind becomes aware of unconscious
decisions as much as 10 seconds later.
Coffee or tea with lunch? Which pants to wear to work? Which movie to watch? Your mind
might be made up before you know it. Researchers have found patterns of brain activity
that predict people's decisions up to 10 seconds before they're aware they've made a
choice.
In the 1980s, psychologist Benjamin Libet of the University of California, San
Francisco, caught people's brains jumping the gun on consciousness. A few hundred
milliseconds before a person thought he or she decided to press a button, brain areas
related to movement were already active. The result was hard for some to stomach because
it suggested that the unconscious brain calls the shots, making free will an illusory
afterthought. But there was room for doubt. The time lag was so short that it might have
been an error, and the brain activity might have reflected preparation for a decision
rather than the decision itself. "It's possibly the most debated single paper in the
whole of neuroscience," says brain scientist John-Dylan Haynes of the
Charité-Universitätsmedizin Berlin in Germany.
To settle some of the doubts, Haynes led a team of researchers in a modern redux of the
experiment. They asked 14 subjects to lie in a functional magnetic resonance imaging
(fMRI) scanner, which allowed the researchers to track more brain regions for longer than
Libet had. They instructed the subjects to decide spontaneously whether to press a button
on the right or one on the left. The volunteers could decide at their own pace, but they
had to report the moment of the conscious choice based on a clocklike device in the
scanner.
The researchers scoured the brain for changes that correlated with the final decision.
The earliest brain pattern that coded for a left or right choice was in the frontopolar
cortex, right behind the forehead. The pattern predicted a left or right decision with
about 60% accuracy and occurred about 10 seconds before the conscious choice, the team
reports online this week in Nature Neuroscience. "We weren't expecting this kind of
lead time," Haynes says. Even though the predictions weren't perfect, "there's
not very much space for operation of free will," Haynes says. "The outcome of a
decision is shaped very strongly by brain activity much earlier than the point in time
when you feel to be making a decision." Haynes says the group hopes to extend the
work to more realistic choices such as what to drink or what game to watch.
Dick Passingham, a cognitive neuroscientist at the University of Oxford in the U.K.,
says the paper clears up one of the major concerns about the original Libet experiment.
"This activity that occurs earlier is ... not just general preparation, it really is
a proper decision," he says.
Neurologist Mark Hallett of the U.S. National Institute of Neurological Disorders and
Stroke in Bethesda, Maryland, says the study confirms his understanding of free will as a
perception rather than a driving force. But he hopes the work may lead to practical
applications for patients with schizophrenia or certain movement disorders who feel that
their voluntary actions are not a product of choice.