The bizarre story of the "sonic weapon" attacks against American and Canadian diplomats based in Cuba has many twists and turns – and apparently, just as many explanations. Possible causes range from silent weapons and mass hysteria to chirping crickets (yes, really).

Naturally, some of these hypotheses are more credible than others, but one thing that does seem to be clear is the very real physical changes in the brains of the diplomats (and relatives of diplomats) affected. Something research published in the Journal of the American Medical Association (JAMA) this week appears to confirm.

Between 2016 and 2018, diplomats reporting attacks described similar symptoms. These included headaches, nausea, insomnia, vertigo, and hearing loss, as well as problems with memory and cognition. Often these sensations would have been preceded by a loud and sudden noise. Some felt vibrations in the air.

Whether or not the trigger was physical or psychosomatic, doctors in Canada and the US have identified brain abnormalities in the affected – including changes to their white matter. Most recently, researchers at the University of Pennsylvania led by Ragini Verma used a series of advanced imaging techniques (including functional, diffusion, and structural MRI) to examine the brain structure of 40 Americans affected and compare the results to a similar-sized control group (48 people).

Verma and colleagues found that the diplomats had lower levels of white matter in the brain and in particular, the cerebellum – an area involved in performing voluntary tasks like walking and writing. The team also found differences in measures of water diffusion in the tissue and lower functional connectivity in the visuospatial and auditory subnetworks. 

"The areas implicated in the patients' brains, namely the cerebellum as well as the visuospatial and auditory networks, align with the neurological symptoms that were observed in the patients," explained Verma, who led another study (published last year) looking into the neurological symptoms of 21 affected diplomats.

"These differences persisted even when people with some history of brain injury were excluded from the analysis."

Curiously, Verma says the patterns of difference do not look like imaging-based investigations into other pathology (for example, concussion or traumatic brain injury). But, Lindsey Collins-Praino at the University of Adelaide in Australia told New Scientist, the fact that differences between the diplomats and controls exist does seem to suggest that there is a neurological basis to the symptoms.

"These findings may represent something not seen before," co-author Douglas H. Smith said in a statement.

One problem the scientists face is that this research is taking place sometime after the incident – whatever it was – took place. That can make it hard to determine whether or not these changes are a result of the attacks (if that is what they were) or of treatment and recovery.

"It's hard to tell where the problem started; the brain differences observed could be an immediate effect of the brain injury, or it could a compensatory effect of the recovery process," Verma continued.

"It's very difficult to say, especially with a retrospective, heterogeneous study, where people were included at various times after potential exposure. The important thing is that we did see differences at the group level."

Cuba has dismissed the findings.