Just as Congress again explores a mystery syndrome among US diplomats in Cuba and China, another crazy explanation for the “concussion-like” symptoms among them has emerged, only to be slapped down by scientists.
The House Foreign Affairs subcommittee devoted to Western Hemisphere matters, chaired by Rep. Paul Cook of California, will hear on Thursday from a multiagency federal task force investigating the debilitating illnesses that affected about two dozen diplomats from the US and Canada.
First made public a year ago by the State Department, the cases started in Cuba in 2016, and were accompanied by reports of “buzzing,” “grinding metal,” “piercing squeals,” or “humming” noises. “We hold the Cuban authorities responsible for finding out who is carrying out these health attacks,” then–secretary of state Rex Tillerson told reporters.
In May of this year, the State Department reported two more cases in China, and Cuba identified another US diplomat with symptoms preceded by “undefined sounds.” In a JAMA study of 21 diplomats, a wide variety of symptoms were reported, including deafness, blindness, vertigo, and difficulty concentrating. Three had “concussion-like” symptoms.
No credible explanation has emerged for the injuries, with theories ranging from ultrasound to poison to infection to mass hysteria. Last week, a UC San Diego School of Medicine professor, Beatrice Golomb, proposed another idea: clicking sounds induced in the inner ear by a beam of microwaves, a theory that had been previously raised by New Scientist magazine in December and the New York Times over the weekend.
“It is plausible that the loud buzzing, burst of sound, or acoustic pressure waves may have been covertly delivered using high-power microwave radiation,” James Lin of the University of Illinois at Chicago wrote in IEEE Microwave Magazine in December.
A microwave-induced sound effect was first reported near radar antennas in 1947, and documented in 1956 in an Airborne Instruments Laboratory report. In subsequent decades, researchers discovered that when a microwave beam of certain frequencies hits the head, it generates tiny heating pulses — around a few millionths of a degree — in the scalp, cerebrospinal fluid, or brain tissue. These pulses create sound waves that ring the head for a few milliseconds, conducted to the inner ear by bone conduction, often leading the person to hear a soft click.
In a statement on her new study of the possible link to the Cuban imbroglio, Golomb said that brain-imaging studies of people affected by microwave pulses “showed evidence of traumatic brain injury, paralleling reports in diplomats.”
Microwave experts, however, expressed deep skepticism.
“The microwave auditory effect is a real stretch. It is a biologically trivial effect due to thermally generated vibrations in the head,” University of Pennsylvania bioengineer Kenneth Foster, who documented the mechanism for the effect in 1974, told BuzzFeed News.
“It takes strong microwave pulses to generate barely detectable sounds in the head, and the sound levels in the head are many orders of magnitude below anything that is reasonably anticipated to be hazardous.”
The clicks are so quiet that in order for participants to hear them in 1970s experiments in a sound chamber at the University of Washington, researchers had to to turn off the computers in the adjacent room, microwave expert Chung-Kwang Chou, who heads an Institute of Electrical and Electronics Engineers (IEEE) committee on the health effects of microwaves, told BuzzFeed News.
What’s more, both Chou and Foster noted that in the effect, the sounds occur entirely inside a person’s head. And that person usually can’t hear them if standing outside or in a noisy room, he said.
That’s not the case for the diplomats: Recordings from Cuba of the sound have been released in news reports. “If it can be recorded, then it is acoustically generated, and not a [microwave-]generated sound in the human head,” Chou said.
The Cuban government and entomologists have suggested that the unexplained sounds came from cicadas. University of Michigan researchers have pointed to unintended interference of ultrasound listening devices as a possible explanation.
As for the concussion-like injuries reported in the diplomats, they have also come under intense criticism from neuroscientists, who suggested the JAMA report set an arbitrarily broad definition for brain injuries that would define 40% of the population as brain-damaged. In August, JAMA published letters from psychologists and neurologists critical of its study for not including mass hysteria as a possible explanation, and not publishing hearing and balance tests.
Some news reports have pointed to a Pentagon “Active Denial System” microwave weapon, meant to break up mobs by triggering burning sensations, as the sort of beam that might have caused the injuries. Chou called that ”way off,” however, because the power intensity of the non-lethal weapon is orders of magnitude higher than the ones triggering the hearing effect, plus it causes painful heating on the skin.
In previous hearings on the diplomats, State Department health officials were unable to conclude what caused their injuries, and the multiagency report has been long awaited because it is expected to include new information from Defense Department investigators. The US pulled staff from Havana and expelled 15 Cuban diplomats over the incident last year, and a yellow “travel advisory” is still in effect for US citizens visiting Cuba.
Rather than causing brain injuries, the hearing effect is so trivial that next week the IEEE will release microwave safety standards reaffirming 2005 findings that it is harmless, Chou added. “I am skeptical about the Cuban case. Without more detailed info, it is just a mystery.”