Reports coming out of Cuba in 2016 were bizarre, mysterious, and alarming: American diplomats in Havana were under attack by a terrifying and powerful—yet invisible—enemy. Victims complained of headaches, dizziness, nausea, and fatigue; some suffered debilitating memory and concentration problems, while others reported hearing loss and tinnitus. The only clue about its origin was that a high-pitched sound was heard at the time. The attacks were, understandably, taken seriously by the State Department; complaints were lodged against China and Russia as Cuban diplomats were expelled from the United States.

The cause of the maladies, and perhaps more importantly who was behind the attacks, was promptly investigated. Neuroscientists at the University of Pennsylvania discovered concussion-like symptoms that, they claimed, had damaged victims’ brains. The cause was “an unknown energy source.” Soon, other seemingly similar incidents were reported, ostensibly verifying the original reports. In 2017 and 2018, for example, a diplomat in an embassy in China reported identical symptoms. Investigations were launched but found no clear evidence of any attack.

What really happened is the topic of the new book Havana Syndrome: Mass Sociogenic Illness and the Real Story behind the Embassy Mystery and Hysteria, by Robert Baloh and Robert Bartholomew. Dr. Baloh is in the Department of Neurology at the David Geffen School of Medicine at UCLA, and Bartholomew is a prolific author and at the Psychological Medicine Department at the University of Auckland in New Zealand. (Full disclosure: I have coauthored two books with Bartholomew.)

The authors make a strong case that mass sociogenic illness (MSI, sometimes called mass hysteria) is a likely culprit and that while this case seems strange and sensational, it’s far from unique:

Many psychogenic outbreaks have involved victims who attributed their symptoms to sound waves. … In fact, concussion-like symptoms have been reported in American soldiers returning home from every major conflict since modern doctors began keeping tabs on troops, from World War I to the fighting in Iraq and Afghanistan.

The clinical diagnoses offered in support of a sonic weapon explanation are more subjective than they first appear; while a broken leg or bullet wound can be discretely verified as a hard outcome, many of the “concussion-like symptoms” are not so easily quantified and validated.

Skeptics noted that sound, per se, cannot physically cause the concussions reportedly found. According to the authors:

[Scientists] were baffled as to how diplomatic staff situated deep within a hotel or in the confines of a house could be targeted. Human hearing ranges between approximately 20 and 20,000 Hertz (Hz). Sounds below 20 Hz are known as infrasound [and] have been difficult to weaponize due to the inability to focus the wavelengths. The main effect on human health is irritation. Sounds at the high end of the spectrum of human hearing is ultrasound [and] are equally difficult to control as they dissipate rapidly as they travel. Even if the sound waves were to reach a building in an effort to target people inside, most of the waves would bounce harmlessly off the walls before reaching their target.

Though scientifically defensible, the sociogenic conclusion was politically and socially untenable. If there were no attacks, then what was going on? What about all the witnesses and evidence? One reason diagnoses of mass hysteria are often rejected and disputed by those affected is because of the common misunderstanding that these events are imaginary, faked, or fraudulent; they are not. A diagnosis of MSI doesn’t mean that anyone is pretending or malingering; it merely means that the illness has an internal (psychological and physiological), not an external (environmental) source.

Baloh and Bartholomew write:

This is the story of how much of the world came to believe in something that never happened. It is an extraordinary tale of international intrigue, flawed science, political ineptitude, and the mating habits of two most unlikely suspects: crickets and cicadas. While parts of the story border on the comical and at times are absurd, this saga has had far-reaching diplomatic repercussions as the fear and mistrust it has sown has threatened to undermine the future of Cuban-American relations.

The book provides a fascinating timeline of the strange events and their aftermath, from political finger-pointing to medical investigations. Conclusive and definitive explanations are not always possible due to a lack of information and myriad other factors. It’s certainly possible that, years or decades from now, the intelligence community will discover proof that some unknown sonic weapon was in fact deployed against the embassy in Havana. But until then, Havana Syndrome (together with Occam’s Razor) makes a compelling case that mass sociogenic illness is a plausible explanation.