A new report claims to have found the cause of "Havana Syndrome": microwave weapons. But the story is far from over.

Back in 2016, staff at the United States and Canadian embassies in Cuba began to experience strange symptoms, including headaches, hearing loss, nausea, anxiety, disorientation, and "cognitive fog", sometimes accompanied by a high-pitched noise and sometimes not. 

Making the experience even more unsettling, some would hear the noise while others standing right next to them would not. Theories have been proposed, from strange acoustic weapons to mass hysteria.

The brains of those affected appear to show there is something going on, with a study published in the medical journal JAMA of 40 of the diplomats showing "significant differences in whole brain white matter volume, regional gray and white matter volume, cerebellar tissue microstructural integrity, and functional connectivity in the auditory and visuospatial subnetworks compared with controls."

The researchers did not, in this case, propose potential sources of the injury but concluded there had been some kind of brain trauma. Cuba, meanwhile, disputed the study, claiming the brain scans were inconclusive.

A new report by the National Academies of Sciences, Engineering, and Medicine now claims to have found the most likely cause of the syndrome.

"The committee found the unusual presentation of acute, directional or location-specific early phase signs, symptoms reported by [the] employees to be consistent with the effects of directed, pulsed radio frequency energy," they write in the report, before going on to rule out other factors such as chemical exposure (from insecticide spraying) due to a lack of evidence of high-level exposures and clinical history being inconsistent with symptoms from those chemicals.

"Overall, directed pulse radio frequency energy, especially in those with the distinct early manifestations, appears to be the most plausible mechanism in explaining these cases," though they add that psychological factors could have added to the symptoms, particularly after the event.

They cite "significant research in Russia/USSR" into the effects of pulsed radio frequency energy, and reports of military personnel in communist countries that were exposed to "non-thermal microwave radiation [and] were said to have experienced headache, fatigue, dizziness, irritability, sleeplessness, depression, anxiety, forgetfulness, and lack of concentration, as well as internal sound perception."

They also refer to the Frey effect, discovered in 1961 by Alan Frey. Frey discovered that following exposure to microwave radiation, humans can experience pressure on the head as well as hearing a "buzz, clicking, hiss or knocking" sound at certain frequencies.

Which all sounds very sci-fi. However, there are reasons to be skeptical about microwave weapons being the cause of Havana Syndrome. Extremely skeptical, in fact. 

First, the report itself did not seek to prove that pulsed radio frequency energy was the cause of the strange symptoms, but instead ruled it as the most plausible of the explanations they have and suggestions that Russia may have developed these weapons during the Soviet era are highly speculative. More importantly, there is no evidence that such weapons do exist or could exist in a way that would cause the described effects to the embassy employees.

"Not a single person who has attempted to link the symptoms to microwave energy has ever described – based on known engineering and science – what this device what would look like, or how it would operate," DC Bureau Chief of Yahoo News points out on Twitter. "Because that's where the entire story falls apart."

The person who first described the mechanism behind the Frey effect, University of Pennsylvania bioengineer Kenneth Foster, told Buzzfeed News that the report makes no plausible case for why the syndrome should be caused by microwaves. The Frey effect requires a lot of energy to make sounds that can barely be heard.

“Maybe someone went to the trouble to truck in a large microwave transmitter to cause the employees to hear ‘clicks,’" Foster told Buzzfeed. "But there are simpler ways to harass people than that."