New imaging techniques can see into the functioning brain, revealing the regions that are active during certain tasks and sensations. Magistretti
 et al., in their Perspective, take this notion one step further and, by careful analysis of the biochemistry that gives rise to imaging signals, they deduce some of the cellular and molecular events that accompany neuronal activity in the working brain, ultimately laying the groundwork for determining the biochemistry that underlies human cognition.

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