That's the reason why so many people are excited about reports like the one just published in Science, Movement Intention After Parietal Cortex Stimulation in Humans. The report itself is extremely straightforward. The authors, a team of French neurosurgeons, used electrodes to stimulate various points on the surface of the brains of seven patients. The patients were all suffering from brain tumours in various places, and they were undergoing surgery to remove them. As often happens, the authors decided to try to squeeze a little research out of the procedure as well.
The authors stimulated points in various areas of the brain, but the most interesting results came from the premotor cortex (the blue area on the picture above) and the posterior parietal cortex (red and yellow).
When certain points on the premotor cortex were stimulated, the patients moved. But they were not aware that they had done so. For example:
...during stimulation patient PM1 exhibited a large multijoint movement involving flexion of the left wrist, fingers, and elbow ... He did not spontaneously comment on this, and when asked whether he had felt a movement he responded negatively.
That's pretty interesting in itself, but even more so is what happened when the posterior parietal cortex got zapped. Stimulation here produced a desire or intention to move, although no movement actually occured:
Stimulation of all these sites produced a pure intention, that is, a felt desire to move without any overt movement being produced... Without prompting by the examiner, all three patients spontaneously used terms such as “will,” “desire,” and “wanting to,” which convey the voluntary character of the movement intention and its attribution to an internal source, that is, located within the self.
And as if that wasn't enough philosophically-provocative fun, high intensity stimulation of the same area made the patients believe that they had in fact moved, although they didn't move a muscle:
[with higher electrode currents] conscious motor intentions were replaced by a sensation that a movement had been accomplished [but] no actual movement was observed. Thus, these patients experienced awareness of an illusory movement. For example, patient PP3 reported after low-intensity stimulation of one site (5 mA, 4 s; site a in Fig. 1), “I felt a desire to lick my lips” and at a higher intensity (8 mA, 4 s), “I moved my mouth, I talked, what did I say?”
Wow. What are we to make of all this?
Penfield found that he could invoke all sorts of things- movements, sensations, memories. But in every instance (hundreds of thousands of individual stimulations- in different locations in each patient- during his career), the patients were aware that the stimulation was being done to them, but not by them. There was a part of the mind that was independent of brain stimulation and that constituted a part of subjective experience that Penfield was not able to manipulate with his surgery.
Penfield called this "double consciousness", meaning that there was a part of subjective experience that he could invoke or modify materially, and a different part that was immune to such manipulation.So Penfield, one of the great pioneers of 20th century neuroscience, claimed that stimulation of the brain could never produce desires or intentions which were experienced as the subject's "own". The person whose brain you were stimulating always felt that whatever happened to them came from outside.
But this French report directly contradicts that. We can only speculate as to why. It could be that Penfield just never hit the right spot, but this seems extremely unlikely, as he did a lot of stimulating over the course of his career. A cynic might ask whether Penfield did observe similar phenomena and just never reported them, but if we're going to go down that road, it's equally likely that these neurosurgeons just made it all up. Fortunately, any neurosurgeon should be able to try to replicate these results with a few prods of an electrode, so it shouldn't take long before the truth becomes clearer.
If these present results hold up, they'll certainly suggest some interesting ideas about the organisation of the brain - such as that the perception of movement depends upon the neurones encoding the intention to move rather than those involved in producing the actual motor act.
It would also be interesting to find out what happens when you simulataneously stimulate the premotor spot which makes your arm move, and the posterior parietal spot which makes you want to move your arm. Would that make you want to move your arm - and do so? If so, that would suggest that something very similar to that is going on whenever we do anything. What is life, but wanting to move, and moving?
But whether that's true or not, intentions (and everything else) are still something that happens in the brain, and the brain is a material object subject to the laws of physics. Neuroscience can tell us how exactly it all fits together, but at the end of the day, it's all a bunch of cells. Free will, in other words, appears to be in trouble, whatever the details of the brain's mechanisms happen to be.
Desmurget, M., Reilly, K., Richard, N., Szathmari, A., Mottolese, C., & Sirigu, A. (2009). Movement Intention After Parietal Cortex Stimulation in Humans Science, 324 (5928), 811-813 DOI: 10.1126/science.1169896