Science News tries to get to the bottom of the weird symptoms that American diplomatic workers experienced in China and Cuba recently… and can’t. A team writing in JAMA found they symptoms similar to those caused by exposure to sound waves just below the threshold of human hearing… but some other folks have followed up to say nah, these brain changes aren’t caused by ultrasonics, at least:
The attacks were supposedly committed with sounds outside the range of human hearing. But generating enough acoustical energy to cause hearing loss and brain damage from those types of sound waves would be no easy feat, says Andrew Oxenham, a hearing researcher at the University of Minnesota in Minneapolis. The intensity of very low frequency infrasound or very high frequency ultrasound drops rapidly over distance, so attackers would need enormous loud speakers to have enough intensity to do neurological harm.
“Even to get across the street and into a building, you’d have to have a loud speaker the size of a building,” Oxenham says.
It might be possible to focus ultrasound into a tight beam to stage a high-intensity ultrasound attack. But even with such a beam it would be difficult to make a device small enough to be used as a handheld weapon, says Tyrone Porter, a biomedical engineer at Boston University. And that device would be more likely to lead to disorientation than brain damage, he says.
[University of Southampton researcher Timothy] Leighton and other scientists have questioned whether the JAMA paper actually measured harm caused by a sonic attack. One symptom investigated in the study, white matter changes in the brain, made headlines. White matter is composed of axons, the long extensions of nerve cells that connect different parts of the brain.
“As a result, people got the impression this was some sort of ultrasonic death rifle,” Leighton says. But only three people in the study had white matter abnormalities, and the researchers couldn’t attribute those changes to a sonic attack. They may just have been physical differences that those people’s brains had all along.
What’s more, in the JAMA study, scores that classified diplomats as having a deficit in brain function fall into humans’ normal variation, says Sergio Della Sala, a cognitive neuroscientist at the University of Edinburgh.