Now, researchers are reporting results from the first brain-imaging studies of 40 of those diplomats, who were carefully examined by neurologists after returning home from Cuba. The study, appearing Tuesday in the medical journal JAMA, concludes that the diplomats experienced some kind of brain trauma. But the nature and cause of that trauma were not clear, as it did not resemble the signature of more familiar brain injuries such as repeated concussions or exposure to battlefield blasts.
“The main thing we can do with brain imaging is ask whether something happened to the brain,” said Dr. Ragini Verma, a professor of radiology at the University of Pennsylvania Perlman School of Medicine and lead author of the new report. “And the answer we found is that yes, it did.”
Based on the findings, Verma said that a wholly psychogenic or psychosomatic cause was very unlikely. “But I don’t know the cause,” she said. “The imaging by itself cannot tell us that.”
Outside experts were divided on the study’s conclusions. Some saw important new evidence; others say it is merely a first step toward an explanation and difficult to interpret given the small number of patients.
“It’s good work, but there’s just not enough here to come to any conclusion,” said Dr. Mark Rasenick, a neuroscientist at the University of Illinois Chicago School of Medicine. Rasenick is a member of the Cuban Academy of Science and has close ties to scientists there who have been skeptical that invisible weapons were involved. “I think the only reason it’s going in JAMA is that it’s such a politically charged topic.”
In an editor’s note, two editors of the journal acknowledged the uncertainties in the findings but added: “These unique data provide additional information and contribute to a growing evidence base that may help in understanding the neurological signs and symptoms experienced by this group of individuals.”
The new study was an extension of examinations, conducted at the University of Pennsylvania Center for Brain Injury and Repair, of several dozen diplomats returning from Cuba. In 2018, the Penn team, which included Dr. Douglas Smith and Dr. Randel Swanson, reported on the first 21 of those patients and identified a range of peculiar and often shared symptoms.
“The unique circumstances of these patients, and the consistency of the clinical manifestations, raised concern for a novel mechanism of a possible acquired brain injury,” that report concluded.
In the new study, the research team focused on those 21 patients and 19 subsequent ones, examining brain areas known to support hearing, balance, and motor control. It also measured each individual’s volume of gray matter, the overall population of neurons; and of white matter, the connective tissue between the neurons. Gray matter makes up the bulk of the brain’s distinct organs, specialized to manage functions like vision, hearing, and movement. White matter comprises the wiring that connects cells and organs into wider circuits. Sharp deficits in either can compromise brain function.
Those measures were then compared to an identical battery of brain images from 48 healthy adults representing the same mix of ages, genders, and educational attainment.
On average, the diplomats had a lower volume of white matter than individuals in the control group. They also showed clear differences in the volume, connectivity, and tissue properties of the cerebellum, which is involved in maintaining balance, and lower connectivity among neurons in the auditory and visual-spatial areas of the brain. The analysis found no difference between the groups in so-called executive-control networks, which are involved in thinking and planning.
The researchers could not say for certain what these differences mean, except that they are consistent with the symptoms the diplomats have reported. The overall pattern was unlike anything found in studies of people with traumatic brain injuries, multiple sclerosis, stroke damage, or other neural disorders.
“If you look at the totality of these findings — an increase in this, a decrease in that — and combine them all, you have a presentation that is very unique to this cohort,” Verma said.
Whether that presentation reflects a physical injury from an enigmatic weapon, or something else, is still far from clear, the authors acknowledged. Reaching a firm conclusion would likely require many more new cases, a situation that nobody is eager to see.