Recently, an editor wrote to me with the following problem: The writer whose novel he was editing wanted to include a scene where a character experiences a rare neurological condition called alien hand syndrome (AHS). With that syndrome, one hand literally does not know what the other hand is doing. For example, while the right hand is buttoning up a shirt, the left hand could be unbuttoning it.

In that case, the left hand appears to have a mind of its own. But does it? The syndrome has sometimes been used to argue for the idea that neurosurgery patients whose brains have been split in half (to combat epilepsy) really have two separate minds (dual consciousness) afterward.

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That idea got started because split brain patients, along with others, do occasionally suffer from this syndrome. It seemed attractive to materialists because it would provide evidence that the mind is merely a function of the brain that has no independent existence.

Anyway, the editor wanted to know what I thought. In particular, how does the syndrome relate to the concept of free will?

First, are there “aliens” involved?

One difficulty with understanding AHS is that we don’t appreciate how automatic our complex actions usually are.

When I’m buttoning my shirt in the morning, I give it virtually no thought at all. I’m thinking about feeding the dog or where I put my wallet, and so forth. We do countless thousands of stereotypical movements each day without giving them more than a millisecond of thought.

Think of all of the muscle activities, sensory input, decisions, etc., needed just to drive a car to work in the morning — our eyes, hands, arms, legs, feet, neck, torso, lungs — all moving in co-ordination. Yet we’re basically not aware of any of these individual actions—we just do them, preconsciously, under the radar while we are thinking about lunch and politics, etc.

Very little of this has anything really to do with will — will is our decision to seek gainful employment, to make moral judgements, to think abstractly (“I’ve got 23 miles until empty, and this commute is 24 miles so…”)

This is part of the difficulty engineers face when they try to make self-driving cars reliable and safe. Trillions and trillions of bits of data go into these systems to do mundane things. Yet distracted 16-year-olds with learner’s permits do these things effortlessly, all while completely preoccupied with the hope of a hot date tonight.

Linguist Noam Chomsky (1928–) talks about this aspect of our lives in terms of how we learn a language. He called it “the paucity of stimulus”; he just meant that humans do many things automatically that would require astronomical amounts of data to replicate in a computer.

We are extraordinarily good at coordinating countless movements without even thinking about it — thus, the surprise, from a medical perspective, is that a problem like Alien Hand Syndrome occurs as rarely as it does.

When automatic systems don’t work, they feel alien

Our normal daily buttoning and unbuttoning of a shirt is basically “alien” in one sense; we don’t really think about it except in a fleeting way. Our hands just do their thing and we only notice if, say, a button is missing.

What happens with AHS is that, due to a bit of brain damage, we don’t coordinate things right—we get buttoning and unbuttoning confused. That may feel spooky but it has nothing to do with the reality of the mind. The mind itself is a unity; it cannot be split.

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Think, for example, of the amazing coordination needed to speak. Diaphragm, larynx, vocal cords, pharynx, palate, tongue, lips are at work, all while we are walking, looking around, and thinking of what to say next and what’s for lunch, etc. If, with so much going on, you misspeak, mispronounce a word, or stammer, that doesn’t mean that you have “alien speech syndrome” and that there are two people living inside you. It just means that you had a little glitch in an unbelievably complicated activity, hopefully not a serious brain issue. If a person has a stroke or a split corpus callosum, the discoordination gets a bit more obvious, but it usually starts to correct after a while.

And in the everyday world …

We should also keep in mind that the vast majority of people with AHS don’t have anything as remarkable as competing hands buttoning things. I’ve never actually seen a case of alien hand syndrome as severe as that. Usually, patients have arms that move a bit when they are distracted, and that corrects itself in short order.

AHS is not evidence of split minds, dual consciousness, or lack of free will. It is just a rare manifestation of a very mundane truth about us — we do countless things constantly that we aren’t ordinarily thinking about. Brain damage can screw that up but, in this case, only transiently.

Could there be neuroscience evidence of split minds or lack of free will?

Here’s a test: How about “Alien Mathematics Syndrome”? Your right hand does new problems in differential calculus while your left hand does new problems in integral calculus. Or ““Alien Opinion Syndrome”? Your right hand types an original pro-life essay and your left hand types an original pro-choice essay. If that happens, I’ll take AHS seriously as a challenge to free will.

But that doesn’t happen — it doesn’t even make any sense. To simultaneously pursue two opposite abstractions or moral objectives isn’t even a meaningful concept, let alone a practical reality. We can be undecided or confused, but to resolve to do opposite things simultaneously defies the meaning of “resolve.”

I’m glad he asked. I hope it helps.