Poldrack on the limits of fMRI

Cerebrum, the Dana Foundation’s neuroscience magazine, has a really nice article on the limits of fMRI by Russ Poldrack. You should go read it, but to summarize some of Poldrack’s main points:

• fMRI studies tell us what’s true of brain activation on the average, but we’re nowhere near the point where fMRI scans have diagnostic value at the level of individual subjects. Put another way, you may be able to tell that people with ADHD have somewhat different neural responses than people without ADHD on average, but you can’t tell whether someone has ADHD or not by looking at their individual brain activation.
• The functional implications of specific differences in brain activation are not always clear. If schizophrenics show more activation in frontal brain regions than healthy controls, is that a good or bad thing? Are the increases reflective of the underlying disorder, or do they represent the brain’s attempt to compensate for the underlying deficit? We just don’t know at this point.
• Scientists and journalists alike are too quick to draw what Poldrack has called the “reverse inference“, arguing that a specific cognitive function must be involved in a certain task on the basis of the spatial location of activation. For example, many researchers who observe increased amygdala activation in response to a particular stimulus are quick to suggest that people are engaging in emotional processing, when in fact the amygdala may be activated by many other types of processes. There just isn’t enough evidence to support most reverse inferences.
• For all of the above reasons (and others), the people selling various fMRI-related services–e.g., “neuromarketing” firms that purport to tell major companies how people “really” feel about their brands–are basically selling snake oil.

Anyway, it’s a good piece, so give it a read. Poldrack is widely respected in the field of cognitive neuroscience for his thoughtfulness and methodological rigor, so it’s always worth paying attention to what he has to say on such matters.

[hat-tip: MindHacks]