Limits of Brain Imaging

This long and thoughtful review of Jonah Lehrer's Imagine nicely explains how brain imaging isn't all it can seem to be.

So how does letting go, Lehrer asks, lead to creativity? “The story begins in the brain,” he claims, and turns to a neuroimaging experiment in which jazz pianists were asked to improvise new tunes while in a brain scanner. During improvisation, the scanner picked up a surge of activity in a brain area previously linked to self-expression. At the same time, the scientists also observed a sharp decrease in brain activity in an area previously linked to impulse control. Lehrer concludes, “This suggests that the musician was engaged in a kind of storytelling, searching for the notes that reflected her personal style…The musicians were inhibiting their inhibitions, slipping off those mental handcuffs.” At first pass, this interpretation sounds pretty convincing: the self-control center of the brain shuts down to clear the path for unfettered self-expression.

Except that it’s impossible to draw that conclusion from the data at hand. This is an example of a common logical fallacy that plagues the interpretation of neuroimaging data. Say you notice a crowd of people at your neighbor’s house one night, and then find out she is throwing a party. You can correctly conclude that whenever your neighbor throws a party, there will be people at her house. On another night, you again notice a crowd of people at her house, and you conclude she is throwing a party — but this time you’re wrong. She is hosting a church group. While you can conclude that a party means there will be people, you cannot conclude that people means a party.

. . . There is not a measurable one-to-one mapping between any brain region and any particular cognitive process; the same little patch of cortex is likely involved in multiple functions, just as a house can be filled with people for many different reasons.