Free will and brain stimulation

A study published recently in Science magazine investigated human volition in patients undergoing brain surgery. Michel Desmurget and his colleagues electrically stimulated the brains of seven subjects awake under local anaesthesia. When the right inferior parietal regions were stimulated, the subjects reported an intention to move their left hand, arm or foot. Stimulation of the left inferior parietal region elicited an intention to talk and move the lips. When regions were stimulated more intensely, the patients believed that they had actually moved those bodily parts, although no movements were in fact performed.

In commenting this study, New Scientist claimed that scientists had found a “possible site of free will.” While one could argue about the wording of that statement, it seems pertinent to consider whether this and similar other studies have implications for the free will debate.

Let us begin by asking why do we think that we have free will in the first place.  The answer, it seems, is that we just feel we do. As I type these words, for instance, it seems to me that I’m in control of what I am doing, and that it is up to me to continue writing this post or to leave it unfinished and go instead to see the swans at Christ Church Meadows (a much more enjoyable activity). And because it appears to us that we are free, it seems reasonable to conclude that we are—unless there are positive reasons for thinking otherwise.

This argument could be contested in two ways. First, one may deny the general principle that, in the absence of countervailing reasons, things are likely to be as they appear. Secondly, one may accept the principle but deny its applicability to the particular case at hand, by pointing to the relevant countervailing reasons.

The general principle has been defended in one way or another by a number of philosophers, including Richard Swinburne, Quentin Smith and Michael Huemer. A denial of the principle seems to open the way for radical skepticism about the external world and, by extension, about other minds, leading to a form of solipsism. So questioning the existence of free will by contesting the connection between appearance and reality seems to carry an excessive epistemic cost. A much less radical strategy is to argue that, in the particular case of free will, there are reasons for thinking that things are not as they appear to be. It is here that scientific studies such as the one conducted by Desmurget et al. may enter the philosophical debate.

As we have seen, strong stimulation of certain brain areas caused subjects to believe that they were freely moving certain parts of their bodies. Yet we know this belief to be false, since the subjects were not moving at all. So here we have an instance in which the subjective experience of free will demonstrably does not correspond to any objective reality; in these cases, the experiences are entirely illusory. Generalizing from this finding, we may conclude that, when it comes to free will, what seems to us to be the case is no guide to what is in fact be the case.

Some philosophers have disputed this kind of move. Thus, Mark Balaguer dismisses a similar study on the grounds that it

is a sort of real-life version of the various alien-manipulation thought experiments that philosophers often discuss. But even if aliens can manipulate our torn decisions, it doesn’t follow that when aliens aren’t present, our torn decisions aren’t libertarian free.

Balaguer is right to point out that, from the fact that our decisions can be manipulated under certain circumstances, it doesn’t follow that they can also be manipulated under all circumstances. But we are often justified in generalizing from a proper subset of cases to the set of all cases, since we have no reasons to believe that there is a relevant difference between the two. Balaguer points to a difference—“aliens are present”/”aliens are not present”—but gives no indication as to why this difference is relevant. (The dowser may similarly refuse to accept that controlled studies disprove dowsing on the grounds that there is a difference between dowsing under controlled conditions and dowsing under normal circumstances.)

Of course, there may be relevant differences. The presence of local anaesthesia may be one of them. My point in the post was not to argue that the study provides evidence against free will, but instead to show how it may do so.

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