Alien Hand Syndrome

This will sound very weird, but there's a phenomenon called alien hand syndrome that bears on the question of free will and determinism. Neuroscientist Michael Egnor explains the condition in an article at Mind Matters:

This neurological condition occasionally afflicts patients who have had split-brain surgery or other procedures or injuries that disconnect regions of the brain. They experience involuntary movements of limbs. Most commonly it is the left arm, which seems to have a mind of its own. The classic example...is a patient who intentionally buttons her shirt with her right hand while her left hand follows, unbuttoning her shirt, which she doesn’t intend!

In other words, the two halves of the brain seem to have conflicting wills which suggests that the will is neither unitary nor free. Here's another example quoted in Egnor's piece:

Another example [is] related to food, where the right hemisphere was not pleased with what the left hemisphere had been cooking and threw a vial of salt on the food, to render it useless. These examples do seem to imply that will and awareness are indeed split, and there is a struggle for power between the two hemispheres, and thus the two sides of the body.

These examples seem, at least at first glance, to support the materialist view that all of our willful decisions are really the product solely of our material brain, but Egnor disagrees:

[A]lien hand syndrome doesn’t mean that free will is not real. In fact, it clarifies exactly what free will is and what it isn’t. We have, broadly speaking, two kinds of volition. In common with animals, we have appetite. Appetite is volition that arises from material processes in the brain.

Appetite may or may not be entirely conscious, but it entails motor acts and perceptions linked to specifics of the environment—a keyboard, a button, a bowl of food, or a sexually attractive person. We, along with non-human animals, experience powerful appetites arising from brain processes (neurochemicals, action potentials, and the like) all of the time.

In fact, appetite is the only type of volition that non-human animals experience.

But human beings have another kind of volition as well. We have will, which, unlike appetite, does not arise from brain processes. Will follows from intellect, which is the human ability to think abstractly, without linking the thought to particular objects.

I may desire an extra slice of cake (appetite), but I think about how bad that would be for my nutritional health (intellect) and decide, based on my abstract concern for my health, to forgo the cake (will). My will can override my appetites.

Because will follows on intellect, which is an immaterial power of abstract thought, will is free, in the sense that it is not determined by physical processes such as brain chemicals. Will is, of course, influenced by physical processes. If I’m really hungry and tired, I may decide to have that piece of cake anyway because my appetite has got the better of my compromised intellect. But I still chose to have the cake.

My choice was not determined by chemistry, although it was influenced by chemistry.

Egnor argues that alien hand syndrome is a phenomenon of appetitive volition rather than of the will:

All of the examples of alien hand syndrome involve particular acts—a hand unbuttoning a button or reaching for an object, and the like. This splitting of volition to do particular acts is splitting of the appetite, not splitting of the will. There are no examples of splitting of the will— no examples of simultaneous distinct abstract intentions.

Now, I don’t mean that we don’t have times of indecision; of course we do. I mean that there are no examples of simultaneous distinct abstract decisions—say, to deliberately will justice and injustice at the same moment or to deliberately do differential calculus and integral calculus (one with the right hand, one with the left) at the same moment.

Will is metaphysically simple, in the sense that it has no parts that can separate completely from one another. In fact, unity of will is more or less what we take to define an individual person. If there are two distinct wills, there are two distinct people. ‘Splitting of the will’ defies what we know to be true of human beings.

It is the abstract nature of will that distinguishes it from appetite and makes it free and metaphysically simple, incapable of being split. Alien hand syndrome is an example of splitting of appetite, which is a brain function driven wholly by material processes.

Thus, alien hand syndrome is not an exception to free will at all. In fact, a proper understanding of alien hand syndrome helps us understand what free will really is.

The fact that split brains can dictate conflicting unconscious behaviors does not seem to be a compelling argument against the existence of an immaterial will. After all, our brains dictate a lot of unconscious behaviors including heartbeats, digestion, the coordinated movements of a baseball player catching a fly ball, etc. All of these are "appetitive" volitions.

Egnor may well be correct in what he writes on alien hand syndrome, and what he says is important, but the most puzzling question of all is still unanswered and probably unanswerable: What, exactly, is the will?