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Wray Herbert

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The Brain Is Not an Explanation

Posted: 03/30/11 10:42 AM ET

"Brain scans pinpoint how chocoholics are hooked."

This headline appeared in the Guardian a few years ago above a science story that began: "Chocoholics really do have chocolate on the brain." The story went on to describe a study that used functional magnetic resonance imaging (fMRI) to scan the brains of chocoholics and non-cravers. The study found increased activity in the pleasure centers of the chocoholics' brains, and the Guardian report concluded: "There may also be some truth in calling the love of chocolate an addiction in some people."

Really? Is that a fair conclusion to draw from the fMRI data in this study, reported in the European Journal of Neuroscience? Brain stories have become incredibly popular in the news pages in recent years -- and brain imaging stories especially, in part because of the colorful "pictures" that often accompany the data and analysis. But how much can we really conclude from these images? How skeptical should we be, as readers of the science pages in the paper?

A growing number of scientists, including neuroscientists themselves, are calling for more caution from scientists, both in reporting and interpreting fMRI data. Among them is University of Illinois neuroscientist Diane Beck, who in a recent article in Perspectives on Psychological Science discussed both the appeal and the pitfalls of popular stories about the brain and behavior.

The difficulties of these stories begin with the technology itself, the sheer complexity of which makes accurate reporting a challenge. Despite those colorful images that grab our attention in the news pages, the fMRI is not a photograph -- not even close. An fMRI image is actually constructed from the complex interplay of radio waves and the magnetic properties of hemoglobin. That familiar head-shaped image is the final product of highly sophisticated mathematics and modeling and statistical analysis -- much of which neuroscientists themselves don't fully understand. The image is many complicated steps away from any actual human behavior -- if that leap can be made at all.

Even this paraphrase of mine is a gross oversimplification. The problem is that the final product -- the brain image -- looks like a photograph, and that's how most readers take it, as a simple snapshot of the brain in action. That's in part because the simplicity of the message is appealing: Complicated behavior X lights up brain area Y. But such reductionism, Beck argues, lacks any explanatory power. Consider the chocoholic example again: Leaving aside the fact that chocoholic is not a recognized diagnosis, what does this study actually show? It shows that people who define themselves as chocolate cravers have more activity, relative to people who do not define themselves as chocolate cravers, in certain pleasures centers of the brain. That is, the sight and taste of chocolate activate the brain's reward system in cravers, documenting... what? Well, documenting that some people find chocolate more rewarding than others. As Beck notes, we probably don't need a brain scan to corroborate what most people already believe anyway.

But it's the brain -- it's biological -- which gives readers more confidence in a behavior than the behavior itself. Why isn't it good enough to simply ask a lot of people if they crave chocolate? Chances are some would say yes and some would say no. The fact that the brain's reward center is relatively more active in cravers doesn't add much -- and it certainly doesn't verify that a self-proclaimed chocoholic is akin to a heroin addict or alcoholic.

The chocoholic study may seem trivial, but is just one of many that Beck analyzes. Another is a 2006 New York Times study of glossolalia -- speaking in tongues -- which documented decreased activity in the prefrontal cortex during this religious practice. In the article, the lead scientist describes this result as consistent with the claims of the speakers that they lack control over their utterances, leaving the impression that the brain image supports the belief that people who speak in tongues are speaking the words of God. But nothing could be further from the truth. The most that we can conclude, Beck argues, is this:

When practitioners claim they are in a different mental state when speaking in tongues than they are when singing gospel music (the comparison condition), their brains corroborate that claim. But that's not an amazing claim. Indeed, it's again a claim that most of us would readily accept, just on the practitioners' say-so. As one media critic asked at the time: "If your test subject tells you he likes ice cream, what do we learn from the fact that his brain thinks so too?"

Explaining brain research is not easy, and Beck's purpose is not to fault particular reporters or news organizations. But she is alerting her scientific colleagues that consumers of science prefer simple messages; have heightened confidence in biological evidence; and often confuse the brain for true explanation. That may be human nature, but scientists should be careful not to play into these pervasive biases.