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An brain imaging technique where a radioactive “marker” that emits, or releases, positrons (parts of an atom that release gamma radiation) is injected into the bloodstream. Detectors outside of the head can sense these “positron emissions,” which are then reconstructed using sophisticated computer programs to create “tomographs,” or computer images. Since blood flow and metabolism increase in
brain regions at work, those areas have higher concentrations of the marker, and researchers are able to see which brain regions are activated during certain tasks or exposure to sensory stimuli.