Group A Streptococcusbacteria -- the cause of strep throat and flesh-eating infections -- have been well studied for nearly a century. But researchers recently made a surprising discovery: strep's M protein alone wipes out macrophages, but not other types of immune cells. The macrophages' self-sacrifice serves as an early warning of infection to the rest of the immune system.

In the largest functional brain imaging study to date, researchers compared 46,034 brain SPECT (single photon emission computed tomography) imaging studies provided by nine clinics, quantifying differences between the brains of men and women.

Experts have provided new guidance in the use of contrast agents during MRI scans. Emerging research suggests gadolinium-based contrast agents, injected in a patient's veins to brighten tissues in MRI images, accumulate in the brain. More than 300 million doses of such drugs have been administered since their introduction in 1987.