modern homunculism - the brain is not an explanation

APS | Brain scans pinpoint how chocoholics are hooked. This headline appeared in The Guardian a couple 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 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 very 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 many who study the brain, 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 in the journals and 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.

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, is certain pleasures centers of the brain. That is, the sight and taste of chocolate activated 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 probably 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.