Hearing loss, dizziness, sleep and vision problems, tinnitus, headaches, fatigue, and now brain damage—these are the symptoms suffered by two dozen U.S. and Canadian diplomats covertly attacked over the past year while serving in Cuba. U.S. officials initially posited that the diplomats were victims of some sort of sonic weapon, but acoustics experts say that’s nearly impossible.
Details of the attacks have slowly become public over the last few months through a combination of media reports and announcements from U.S. officials. Many details are still unclear. Here, we stitch together the information available, and explain why the diplomats’ health problems almost certainly couldn’t have been caused by an acoustic weapon.
The attacks began in late 2016 when several people serving at the U.S. Embassy in Havana began suffering unexplained health problems, according to the AP, which first reported the story in August this year. U.S. officials spoke to the AP on the condition of anonymity and attributed the symptoms to a covert sonic weapon. Several Canadian diplomats also experienced symptoms.
The U.S. Department of State in September publicly confirmed the attacks, but federal spokespeople avoided speculation about who or what caused them. The diplomats’ symptoms began while they were in their residences or in hotels, the feds confirmed. Onset of the symptoms in some cases were accompanied by audible, agonizing sounds, and in other cases by no sound, according to media reports.
Health problems for the victims then ensued, and included hearing loss, dizziness, balance problems, difficulty sleeping, ear-ringing (tinnitus), headaches, fatigue, and “cognitive issues,” according to the State Department. The American Foreign Service Association, after meeting with some of the victims, added to that list: cognitive disruption, mild traumatic brain injury, and brain swelling.
U.S. officials have called the attacks “ongoing” and in October said that two more U.S. government personnel had experienced symptoms, bringing the total number of victims to 24. The State Department has since reduced its personnel in Cuba and warned U.S. citizens not to travel there. Cuba has denied involvement in the attacks, and put forward its own theories.
Then last week, the AP reported that “medical testing” revealed that the embassy workers had “developed changes to the white matter tracts” of their brains. The organization said it obtained the information from U.S. officials who asked to remain anonymous.
White matter tracts are a type of tissue in the brain that coordinates communication and serves as connections between brain cells, or gray matter. The AP story did not describe what kind of testing or brain scans were performed, nor how the doctors knew that the white matter changes were caused by the attacks.
Regardless, it is highly unlikely that a covert sonic weapon could cause the range of health problems experienced by the diplomats, say acoustic experts contacted by IEEE Spectrum. “It’s not that easy to damage the brain with acoustics,” says Elisa Konofagou, a bioengineer at Columbia University in New York who has studied the effects of ultrasound on mouse and monkey brains, and was not involved in the Cuba investigation.
An ultrasonic device, which propagates acoustic waves in frequencies above the audible range for humans, would have to be in close contact with the body in order to deliver waves below the skin’s surface. “If you take an [ultrasound] transducer and shoot it through the air, virtually nothing will propagate,” no matter how powerful the transducer is, says Konofagou.
And even if someone somehow put an ultrasound device in contact with the victims’ heads without them knowing it, it’s hard to believe that such a device would target only white matter tracts, she says. “Why is the rest of the brain intact? Why would [the weapon] be so selective? That doesn’t make sense to me,” she says.
Konofagou and her team have been researching ways to deliver drugs to the brain using gas bubbles activated by ultrasound. Through that work, they have identified a range of intensities that are safe on mouse and monkey brains and then studied what happens when they use intensities outside that range. They have found that if there’s damage, it’s usually to gray matter, and rarely if ever to white matter, she says.
On the other side, acoustic waves from an infrasonic device, which would have frequencies below the audible range for humans, can travel long distances. Such devices don’t have to be in direct contact with the body. But “the wavelengths are huge, so it would be extremely difficult to focus it on the brain only,” or even on one particular person from a long distance, Konofagou says.
And besides, in order to generate a lot of power, or decibels, an infrasonic device would have to be unrealistically large, according to F. Joseph Pompei, founder of directional sound company Holosonics, who spoke with the AP and Snopes.com on the matter. Covertly deploying such a hunk of machinery would be tough. Plus, it’s unlikely that it could have any significant health effect on the human body, says Jürgen Altmann, a physicist at Technische Universität Dortmund, in Germany, who has studied the history [PDF] and the potential for such devices, and surveyed the literature on health effects.
Not that militaries globally haven’t tried to build such weapons. “Development and testing [of acoustic weapons] has gone on in several directions, but to my knowledge have not resulted in actual devices deployed,” says Altmann.
Konofagou hypothesizes that whatever did happen to the Cuba victims, it started with the white matter, and that affected the victims in different ways due to their varying physiology, thus producing the wide range of symptoms. “The fact that it was so highly targeted, it has to be something more specific to the anatomy and the chemistry” of the brain, she says.
Emily Waltz is a contributing editor at Spectrum covering the intersection of technology and the human body. Her favorite topics include electrical stimulation of the nervous system, wearable sensors, and tiny medical robots that dive deep into the human body. She has been writing for Spectrum since 2012, and for the Nature journals since 2005. Emily has a master's degree from Columbia University Graduate School of Journalism and an undergraduate degree from Vanderbilt University. She aims to say something true and useful in every story she writes. Contact her via @EmWaltz on Twitter or through her website.