 |
| ©cartoonstock.com |
I was set off today by a report that “fMRI scans prove music is more emotionally stimulating if you listen with your eyes closed”. What’s wrong with that? Well, if I want to know if music is more stimulating with the eyes closed, the sensible experiment would be to ask people to report their emotions while listening to music with eyes open or shut. A brain scan gives you a 3D representation of how regional blood flow changes over time when a person performs a particular task or experiences a specific mental state: it does not measure emotional stimulation.
It seems every week we have another claim that brain scans have shown something about our cognitive or emotional characteristics. To see how accurate this perception was, I tried Googling the phrase “brain scans show” or “brain scans prove”. Within minutes I had a long list of hits, most of which made unsupportable claims.
Neuroscientists have for many years been interested in documenting how brain activity in different brain regions correlates with mental activity or mental states. For some mental states, we know enough to say that when we do cognitive operation X, or experience emotion Y, brain region Z is usually activated. But what we can’t say is that if we see activation in Z, this is equivalent to cognitive operation X or emotion Y. For a start, most mental activities involve a whole network of brain regions acting together, and there can also be substantial variation from one person to another in brain structure and function. But more seriously, there is a logical problem at the heart of this argument. Consider not the brain but the skin. When I am anxious, I tend to sweat. If you observe that I am sweating, you may suspect that I am anxious. But I could be sweating for other reasons: I may have been exercising, the room may be hot, or I may have been eating chillis or taking medication. You could test your theory that I am anxious by asking me. Suppose I deny being anxious: would you believe me? Maybe not: perhaps I am really anxious but reluctant to admit it. But you’d be foolish to regard sweating as a more reliable indicator of my emotion than my verbal report unless there was good reason to believe I might be lying. You’d be even more foolish to assume that I’m not anxious if I’m not sweating. Sweating is a correlate of anxiety (and an unreliable one at that): it is not the same thing as anxiety.
But it seems that in the media, there is a belief that activity from a brain scan provides a direct measure of specific mental states; not only that, the brain scan is seen as a more reliable indicator than traditional behavioural measures. You may find it instructive to consider the claims made in the links below, and then consider how they’d look if you took away the phrase ‘brain scans show”. In general, you can see that the brain scan adds nothing: you could test each of these notions with behavioural data. It’s also worth considering how you’d react if a behavioural study and a brain scan study obtained opposing results. A prudent response would be to trust the behaviour. I've got nothing against fMRI studies as a method for studying brain-behaviour relationships: my criticism is for those who interpret the brain activity as if it was the behaviour. As Neuroskeptic put it in a post last year, “Brain scans prove that the brain does stuff”.This was the one Google result that cheered me up. Here are the others:
Brain scans prove ‘that loving feeling’ truly is addictive
Acupuncture reduces pain perception, brain scans show
Brain Scans Show Women Feel More Pain Than Men
Posts
