Volunteers search for needles and other drug paraphernalia along Church Street in Austin, Ind., in April. The region has recorded 142 new HIV cases since December, according to the state, in an outbreak tied to injected-opioid use. Seth Herald/Nurphoto/Corbis hide caption

itoggle caption Seth Herald/Nurphoto/Corbis

Science-based guidelines say there's no benefit to getting an EKG of heart activity before routine cataract surgery — even if the patient is old. But most doctors order such tests anyway. Bull's Eye/ImageZoo/Corbis hide caption

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Colored brain scan of a 17-year-old boy with mad cow disease. The bright yellow spots are a sign that the thalamus is damaged by diseased proteins. Simon Fraser/Science Source hide caption

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Sequencing the genes of a cancer cell turns up lots of genetic mutations — but some of them are harmless. The goal is to figure out which mutations are the troublemakers. Kevin Curtis/Science Source hide caption

itoggle caption Kevin Curtis/Science Source

To sleep, perchance to consolidate important connections in far-flung parts of the brain. Alberto Ruggieri/Illustration Works/Corbis hide caption

itoggle caption Alberto Ruggieri/Illustration Works/Corbis

Some researchers recommend starting mammogram screening at age 40, while others say age 50. Some doctors think screening should be based on a woman's overall risk for breast cancer, not just her age. Hero Images/Corbis hide caption

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The same nerve receptor that responds to the green paste on your sushi plate is activated by car exhaust, the smoke of a wildfire, tear gas and other chemical irritants. iStockphoto hide caption

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