The National Institutes of Health completed two yearslong studies that did not find any noticeable differences in the brains of people who are believed to have “Havana syndrome” and those who don’t.

“Havana syndrome” is the name given to a mysterious illness that a small group of American diplomats and spies overseas have reported since 2016. U.S. diplomats and members of the intelligence community in different locations reported symptoms that include dizziness, head pain, vision problems, cognitive troubles, vertigo, and possibly traumatic brain injuries beginning at the U.S. Embassy in Cuba in 2016.