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Tuesday, April 15, 2008

Brain Activity Prior to Conscious Awareness

A recent study in Nature Neuroscience has sent freewheeling free will discussion aflutter.  Here's the abstract:

There has been a long controversy as to whether subjectively 'free' decisions are determined by brain activity ahead of time. We found that the outcome of a decision can be encoded in brain activity of prefrontal and parietal cortex up to 10 s before it enters awareness. This delay presumably reflects the operation of a network of high-level control areas that begin to prepare an upcoming decision long before it enters awareness.

For some discussion, see here (Wired), here (Wired Interview), here (Boston Globe), and here (Health LawProf Blog).  Here's a sample from the Wired article:

The decision studied -- whether to hit a button with one's left or right hand -- may not be representative of complicated choices that are more integrally tied to our sense of self-direction. Regardless, the findings raise profound questions about the nature of self and autonomy: How free is our will? Is conscious choice just an illusion?

"Your decisions are strongly prepared by brain activity. By the time consciousness kicks in, most of the work has already been done," said study co-author John-Dylan Haynes, a Max Planck Institute neuroscientist.

Haynes updated a classic experiment by the late Benjamin Libet, who showed that a brain region involved in coordinating motor activity fired a fraction of a second before test subjects chose to push a button. Later studies supported Libet's theory that subconscious activity preceded and determined conscious choice -- but none found such a vast gap between a decision and the experience of making it as Haynes' study has.

In the seven seconds before Haynes' test subjects chose to push a button, activity shifted in their frontopolar cortex, a brain region associated with high-level planning. Soon afterwards, activity moved to the parietal cortex, a region of sensory integration. Haynes' team monitored these shifting neural patterns using a functional MRI machine.

Taken together, the patterns consistently predicted whether test subjects eventually pushed a button with their left or right hand -- a choice that, to them, felt like the outcome of conscious deliberation. For those accustomed to thinking of themselves as having free will, the implications are far more unsettling than learning about the physiological basis of other brain functions.

Posted by Adam Kolber on April 15, 2008 at 11:51 AM | Permalink


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I think this only seems troubling if you assume that the non-consciously aware components of a decision are somehow "not you," or not influenced by prior conscious deliberation or the potential for later deliberation. But I think all of those assumptions are suspect.

Posted by: Bruce Boyden | Apr 15, 2008 5:23:31 PM

Interesting. I suspect that the length of this delay explains why some people are good at video games and some are not through fast "reflexes"

Posted by: Michael Risch | Apr 15, 2008 1:24:31 PM

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