More recently, a paper from the lab of Mriganka Sur at MIT reported that the vast majority of the signal detected by fMRI machines was actually a byproduct of astrocytes, which are common cells in the brain that provide neurons with oxygen and energy. When the activity of astrocytes was blocked, but the activity of neurons remained unchanged, 80 to 90 percent of the fMRI signal disappeared. This suggests that fMRI machines are vulnerable to any disorder or drug that leads to changes in astrocyte function, since such changes will dramatically skew the imaging data. "Astrocytes remain so poorly understood," says Sur, "but researchers should keep in mind that astrocytes are largely what fMRI is measuring, and not neural activity directly."
Last year, the New York Times published an op-ed that used fMRI to investigate the brains of swing voters as they stared at photos and videos of presidential candidates. For instance, the scientists found that pictures of Mitt Romney led to activity in the amygdala, while pictures of Hillary Clinton activated the anterior cingulate. (Interestingly, the only two candidates who inspired "little activity in areas of the brain associated with thought or feeling" were Barack Obama and John McCain.)
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