Recent research found that a diminished sense of smell predicted frontal lobe damage in 231 soldiers who had suffered blast-related injuries on the battlefield. In the Department of Defense study led by Michael Xydakis of the Uniformed Services University of the Health Sciences, subjects with low scores on a smell test were three times as likely to show evidence of frontal lobe damage during brain imaging than those whose sense of smell was normal.

— Read more at Smell Tests Could One Day Reveal Head Trauma and Neurodegenerative Disease at Scientific American.