Field of Science

Recent Findings Don't Prove there's a Ghost in the Machine (Sorry Saletan)

When I took intro to psychology (way too long ago), the graduate instructor posed the following question to the class: Does your brain control your mind, or does your mind control your brain? At first I thought this was a trick question -- coming from most neuroscientists or cognitive scientists it would be -- but she meant it seriously.

On Tuesday, William Saletan at Slate posed the same question. Bouncing off recent evidence that some supposedly vegetative patients are in fact still able to think, Saletan writes, "Human minds stripped of every other power can still control one last organ--the brain."


Every neuroscientist I've talked to would read this as a tautology: "the brain controls the brain." Given the gazillions of feedback circuits in the brain, that's a given. Reading further, though, Saletan clearly has something else in mind:

We think of the brain as its own master, controlling or fabricating the mind ... If the brain controls the mind this way, then brain scanning seems like mind reading ... It's fun to spin out these neuro-determinist theories and mind-reading fantasties. But the reality of the European scans is much more interesting. They don't show the brain controlling the mind ... The scans show the opposite: the mind operating the brain."

Evidence Mind is Master

As I've already mentioned above, the paragraph quoted above is nonsensical in modern scientific theory, and I'll get back to why. But before that, what evidence is Saletan looking at?

In the study he's talking about, neuroscientists examined 54 patients who show limited or no awareness and no ability to communicate. Patients brains were scanned while they were asked to think of motor activities (swinging a tennis racket) or navigation activities (moving around one's home town). 5 of the 54 were able to do this. They also tried to ask the patients yes-no questions. If the answer was 'yes', the patient was to think about swinging a tennis racket; if 'no', moving around one's home town. One patient was able to do this successfully.

Note that the brain scans couldn't see the patient deciding 'yes' or 'no' -- actually, they couldn't see the patient deciding at all. This seems to be why Saletan thinks this is evidence of an invisible will controlling the physical brain: "On the tablet of your brain, you can write whatever answer you want."

The Mistake

The biggest problem with this reasoning is a misunderstanding of the method the scientists used. FMRI detects very, very small signals in the brain. The technology tracks changes in blood oxygenation levels, which correlates with local brain activity (though not perfectly). A very large change is on the order of 1%. For more complicated thoughts, effect sizes of 0.5% or even 0.1% are typical. Meanwhile, blood oxygen levels fluctuate a good deal for reasons of their own. This low signal-to-noise ratio means that you usually need dozens of trials: have the person think the same thoughts over and over again and average across all the trials. In the fMRI lab I worked in previously, the typical experiment took 2 hours. Some labs take even longer.

To use fMRI for meaningful communication between a paralyzed person and their doctors, you need to  be able to detect the response to an individual question. Even if we knew were to look in the brain for 'yes' or 'no' answers -- and last I heard we didn't, but things change quickly -- its unlikely we could hear this whispering over the general tumult in the brain. The patients needed to shout at the top of their lungs. It happens that physical imagery produces very nice signals (I know less about navigation, but presumably it does, too, or the researchers wouldn't have used it).

Thus, the focus on visual imagery rather than more direct "mind-reading" was simply an issue of technology.


The more subtle issue is that Saletan takes dualism as a starting point: the mind and brain are separate entities. Thus, it makes sense to ask which controls the other. He seems to understand modern science as saying the brain controls the mind.

This is not the way scientists currently approach the problem -- or, at least, not any I know. The starting assumption is that the mind and brain are two ways of describing the same thing. Asking whether the mind can control the brain makes as much sense as asking whether the Senate controls the senators or senators control the Senate. Talking about the Senate doing something is just another way of talking about some set of senators doing something.

Of course, modern science could be wrong about the mind. Maybe there is a non-material mind separate from the brain. However, the theory that the mind is the brain has been enormously productive. Without it, it is extremely difficult to explain just about anything in neuroscience. Why does brain trauma lead to amnesia, if memories aren't part of the brain? Why can strokes leave people able to see but unaware that they can see?

Descartes' Error

A major problem with talking about the mind and brain is that we clearly conceptualize of them differently. One of the most exciting areas of cognitive science in the last couple decades has looked at mind perception. It appears humans are so constructed that we are good at detecting minds. We actually over-detect minds, otherwise puppet shows wouldn't work (we at least half believe the puppets are actually thinking and acting). Part of our concept of mind is that it is non-physical but controls physical bodies. While our concept of mind appears to develop during early childhood, the fact that almost all humans end up with a similar concept suggests that either the concept or the propensity to develop it is innate.

Descartes,  who produced probably the most famous defense of dualism, thought the fact that he had the concept of God proved that God exists (his reasoning: how can an imperfect being have the thought of a perfect being, unless the perfect being put that thought there?). Most people would agree, however, that just because you have a concept doesn't mean the thing the concept refers to exists. I, for instance, have the concept of cylons, but I don't expect to run into any.

Thus, even as science becomes better and better at explaining how a physical entity like the brain gives rise to our perceptions, our experience of existing and thinking, the unity of mind and brain won't necessarily make any more intuitive sense. This is similar to the problem with quantum physics: we have plenty of scientific evidence that something can be both a wave and a particle simultaneously, and many scientists work these theories with great dexterity. But I doubt anyone really has a clear conception of a wave/particle. I certainly don't, despite a semester of quantum mechanics in college. We just weren't set up to think that way.

For this reason, I expect we'll continue to read articles like Saletan's long in the future. This is unfortunate, as neuroscience is becoming an increasingly important part of our lives and society, in a way quantum physics has yet to do. Consider, for instance, insanity pleas in the criminal justice system, lie detectors, and so on.

1 comment:

Anonymous said...

Good post -- you should put up the content in the comment thread on the article!

PS: I'm sure the Invisible Pink Unicorn (bless Her pointy horn) is hurt that you didn't use Her as your example of a conceivable thing that you're not likely to see. ;-)