Free will, or at least the place where we decide to act, is sited in a part of the brain called the parietal cortex, new research suggests.
When a neurosurgeon electrically jolted this region in patients undergoing surgery, they felt a desire to, say, wiggle their finger, roll their tongue or move a limb. Stronger electrical pulses convinced patients they had actually performed these movements, although their bodies remained motionless.
鈥淲hat it tells us is there are specific brain regions that are involved in the consciousness of your movement,鈥� says (pdf format), a neuroscientist at the CNRS Cognitive Neuroscience Centre in Bron, France, who led the study.
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Brain stimulation
Sirigu鈥檚 team, including neurosurgeon Carmine Mottolese, performed the experiments on seven patients undergoing brain surgery to remove tumours.
In all but one case, the cancers were located far from the parietal cortex and other areas that Mottolese stimulated. One patient鈥檚 tumour sat near the parietal cortex, but did not interfere with the experiments, Sirigu says.
And because the patients were awake during the surgery, they could answer questions.
鈥淒id you move?鈥� a researcher asked a 76-year-old man after lightly zapping a point on his parietal cortex.
鈥淣o. I had a desire to roll my tongue in my mouth,鈥� he responded.
After a stronger pulse to the parietal cortex, a 42-year-old man exclaimed: 鈥淢y hand, my hand moved.鈥� Sirigu鈥檚 team saw no signs of movement.
Action loop
Sirigu鈥檚 team also discovered that stimulating another brain area 鈥� the premotor cortex 鈥� provoked involuntary, unconscious movements in the same patients.
The team鈥檚 work points to two brain areas involved in the decision to move a limb and then execute the action. Sirigu speculates that the parietal cortex makes predictions about future movements and sends instructions to the premotor cortex, which returns the outcome of the movement to the parietal cortex.
In day-to-day life, we rely on both brain regions to move about, she says. 鈥淵ou need both systems, the parietal and premotor cortex to generate intention and check whether this is followed through.鈥�
鈥楪round breaking鈥�
, a neuroscientist at University College London, says the experiment breaks ground because it pinpoints volition to a specific part of the brain, allowing scientists to experimentally control it.
鈥淭hat鈥檚 extremely interesting, because up to now it has been very difficult for neuroscientists to deal with the idea of intentions or wishes or will,鈥� he says.
However, Haggard says no one should be surprised that the experience of volition can be liked to specific brain areas. 鈥淚 can鈥檛 think of any way you can have conscious experience other than as a result of neurons in your brain firing.鈥�
Journal reference: (DOI: 10.1126/science.1169896)
