Think about the last time you got bored with the TV channel you were watching and decided to change it with the remote control. Or a time you grabbed a magazine off a newsstand, or raised a hand to hail a taxi. As we go about our daily lives, we constantly make choices to act in certain ways. We all believe we exercise free will in such actions – we decide what to do and when to do it. Free will, however, becomes more complicated when you try to think how it can arise from brain activity.
Do we control our neurons or do they control us? If everything we do starts in the brain, what kind of neural activity would reflect free choice? And how would you feel about your free will if we were to tell you that neuroscientists can look at your brain activity, and tell that you are about to make a decision to move – and that they could do this a whole second and a half before you yourself became aware of your own choice?
Scientists from UCLA and Harvard -- Itzhak Fried, Roy Mukamel and Gabriel Kreiman -- have taken an audacious step in the search for free will, reported in a new article in the journal Neuron. They used a powerful tool – intracranial recording – to find neurons in the human brain whose activity predicts decisions to make a movement, challenging conventional notions of free will.
Fried is one of a handful of neurosurgeons in the world who perform the delicate procedure of inserting electrodes into a living human brain, and using them to record activity from individual neurons. He does this to pin down the source of debilitating seizures in the brains of epileptic patients. Once he locates the part of the patients’ brains that sparks off the seizures, he can remove it, pulling the plug on their neuronal electrical storms.
Such epileptic seizures are random. No one knows when to expect them, so after the electrodes are implanted everybody sits around and waits. This gives researchers a unique opportunity to observe human neurons in action: During the wait, patients may volunteer to participate in experiments, allowing scientists to discover what functions the recorded neurons carry out. The invasive surgery required to implant electrodes (performed routinely in animals like rats and monkeys for research) cannot be done in humans unless a medical condition (such as epilepsy that does not respond to drugs) calls for it. Such investigations are, therefore, rare.
Fried and his colleagues implanted electrodes in twelve patients, recording from a total of 1019 neurons. They adopted an experimental procedure that Benjamin Libet, a pioneer of research on free will at the University of California, San Francisco, developed almost thirty years ago: They had their patients look at a hand sweeping around a clock-face, asked them to press a button whenever they wanted to, and then had them indicate where the hand had been pointing when they decided to press the button. This provides a precise time for an action (the push) as well as the decision to act. With these data the experimenters can then look for neurons whose activity correlated with the will to act.
Such neurons, they found, abound in a region of the frontal lobe called the supplementary motor area, which is involved in the planning of movements. But here is the interesting thing: about a quarter of these neurons began to change their activity before the time patients declared as the moment they felt the urge to press the button. The change began as long as a second and a half before the decision, and as early as seven tenths of a second before it, this activity was robust enough that the researchers could predict with over 80 percent accuracy not only whether a movement had occurred, but when the decision to make it happened.
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