But a few researchers are finding hints of a physical cause. In February, a team at the University of Pennsylvania described neurological deficits in embassy personnel who had reported symptoms. And in unpublished results, Michael Hoffer, an otolaryngologist at the University of Miami in Florida, and his colleagues describe a unique vestibular and cognitive disorder in two dozen people evacuated from the Havana embassy. They believe some kind of directed energy device may have caused inner-ear damage.

Taking both teams’ observations together, “It seems like something’s going on,” says Lee Goldstein of Boston University, who studies neurodegenerative diseases. But, he adds, “We’re still very much in the early days of trying to figure this out.”