Brain scans show "significant neuroimaging differences" in 40 U.S. embassy employees affected by mysterious neurological symptoms in Cuba in late 2016, according to a study released Tuesday.
The diplomats had significantly smaller amounts of white brain matter, and markedly lower levels of connectivity between parts of the brain responsible for sight and hearing, said the study, published by the Journal of American Medicine.
Researchers from the University of Pennsylvania performed the magnetic resonance imaging scans on the personnel between August 2017 and June 2018. They then compared the images to results from 48 controls.
Employees at the time reported hearing loud buzzing, "piercing squeals" and "mechanical-sounding" noises, in what the Trump administration termed a "sonic attack."
Diplomats said they suffered persistent ear pain, headaches and problems with memory, concentration, balance, sleeping and more.
Many were out of work at least briefly, with half going on sleep or headache medication and three receiving hearing aids, according to CNN.
Weapons or crickets?
Some theorized the symptoms' source were weapons emitting damaging sound or microwaves, though some scientists later argued the strange sounds were simply the loud species of cricket commonly found in Cuba.
Another group of researchers found the sounds could be caused by ultrasound signals from everyday devices crossed with signals from a surveillance system.
During the uproar, the State Department cut staff at the embassy by more than half.
The researchers couldn't link the results to any specific health impacts, emphasizing that the results weren't consistent with any known brain disorders.
The study's small sample size and unclear results have prompted skepticism from other scientists.
Sergio Della Sala, a cognitive neuroscience professor at the University of Edinburgh, called the study "half-baked," in an email to Reuters, noting that 12 of the employees had histories of concussions and none of the controls did.
According to the study, the employee's concussion symptoms had faded by 2016, when reports of illness began.
Diplomats at the Canadian embassy complained of similar afflictions. Five of them and their families are now suing the Canadian government, saying it "downplayed the seriousness of the situation, hoarded and concealed critical health and safety information, and gave false, misleading and incomplete information to diplomatic staff."
In addition to the Penn study, the National Institutes of Health is conducting its own "brain injury research study" involving the Cuba patients with help from the U.S. Energy Department supercomputers and national laboratories capable of processing massive amounts of neurological data. The Defense Department has also been engaged to look into technologies that could have been used to harm the diplomatic staff.