One of the year's most popular posts examined the evolutionary pull of running and high-aerobic activities on our brains. Above, a man runs past the Sydney Harbour Bridge in April.
Ryan Pierse/Getty Images
Researchers at the U.S. Geological Survey National Wildlife Health Center in Madison, Wis., use eggs to see if the Asian strain of the H5N1 bird flu virus has entered the U.S. in this photo from 2006.
Mosquitoes like this one can carry the virus that causes dengue fever, which may become a bigger problem in some regions as biodiversity is lost.
James Gathany/CDC Public Health Image Library
Brain scans using Amyvid dye to highlight beta-amyloid plaques in the brain. Clockwise from top left: a cognitively normal subject; an amyloid-positive patient with Alzheimer's disease; a patient with mild cognitive impairment who progressed to dementia during a study; and a patient with mild cognitive impairment.
Slide courtesy of the journal Neurology
Doctors used a type of MRI test to look at the blood vessels in the brain of a woman with dystextia. The test confirmed she was suffering from a stroke on the right side of her brain
Archives of Neurology
Doctors use tissue slides like this one of the ovary's outer cortex to confirm a woman's ovarian reserve. It's also the the ovary tissue that's removed in an ovarian transplant.
Courtesy of the Infertility Center of St. Louis
Kristen Miller, a colonoscopy patient, sits with Dr. Stephen Hanauer at the University of Chicago Medical Center in Chicago in 2010. They're looking at an interactive computer program describing benefits and risks of the procedure.