Functional magnetic resonance imaging--or fMRI--has made quite a splash since its introduction a decade ago. Operating at spatial dimensions and time-scales far finer than previous brain-scanning techniques, it has sparked great excitement by letting us finally watch the brain at work. Thousands of fMRI studies have explored a wide range of differences in brain activation: adolescents versus adults, schizophrenic and normal minds, the empathetic and the impassive. Researchers have used fMRI to draw bold conclusions about face and word recognition, working memory and false memories, people anticipating pain, mothers recognizing their children, citizens pondering ethical dilemmas--not to mention why many consumers buy Coke even though they really prefer the taste of Pepsi. Psychologists have praised fMRI for finally making their science more quantifiable. And cognitive neuroscientists have cited the scans heavily in the recent, vast expansion in understanding of the brain.

Increasingly, however, arguments are stirring over the reliability of fMRI findings. This debate, at once technical and philosophical, concerns both fMRI's accuracy, because it measures neuronal activity indirectly by detecting associated increases in blood flow, and its legitimacy in linking complex mental functions to particular brain regions. Critics feel that fMRI overlooks the networked or distributed nature of the brain's workings, emphasizing localized activity when it is the communication among regions that is most critical to mental function.

This article was originally published with the title Fact or Phrenology?.

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