A perplexing illness that began striking US overseas diplomats in 2016 did not leave any lasting traces of brain damage, according to the findings of two new brain-imaging studies. Popularly known as Havana syndrome, the strange condition typically involves dizziness, headaches, and blurred vision among other neurocognitive symptoms, yet the cause of the illness remains a complete mystery.

Theories regarding the nature of the syndrome began to spread when the first cases were reported among government staff at the US embassy in Havana, Cuba. Sufferers claimed to have heard loud noises and felt a sense of pressure in their heads, before going on to develop a range of other symptoms, including insomnia.

Labeled anomalous health incidents (AHIs) by US health officials, these odd ailments were soon reported by workers at other American embassies in China and Austria. Despite a lack of solid evidence, many observers – including high-profile politicians – began propagating the idea that the illness was being triggered by some sort of pulsed energy attack, though exactly what kind of weapon could produce such symptoms is currently unclear.

Heightening the sense of panic, a study published in 2019 found that Havana syndrome sufferers had reduced white matter and functional connectivity in the auditory and visuospatial subnetworks of the brain. However, this data has now been challenged by a pair of new studies that did not find any clinical differences between individuals with the condition and healthy controls.

The first of these involved 81 people who experienced Havana syndrome and 48 unaffected individuals. After conducting magnetic resonance imaging (MRI) scans on each participant, the researchers found no significant differences in brain structure or function between the two groups.

“From these findings, it may be concluded that, from a structural MRI standpoint, there was no evidence of widespread brain lesions in the AHI group,” they write. Importantly, follow-up scans also revealed that the brains of people with Havana syndrome remained stable over time, “suggesting absence of evolving lesions.”

“Lack of evolving lesions may indicate absence of an acute brain injury, since most injuries result in changes over time,” conclude the researchers. Despite this, they state that the fact that their study “did not identify a neuroimaging signature of brain injury in this AHI cohort does not detract from the seriousness of the clinical condition.”

The second study compared the MRI scans of 86 people with Havana syndrome with those of 30 controls. Once again, no significant detectable differences between the two groups were observed.

Cautiously interpreting their data, the authors write that "a lack of evidence for a brain injury does not necessarily mean that no injury is present or that it did not occur at the time of the AHI." They also note that despite the absence of brain damage, 28 percent of those with the syndrome showed signs of “functional neurological disorders”, such as persistent postural-perceptual dizziness (PPPD).

“It is also possible that those with AHIs may be experiencing the results of an injury that led to PPPD and other symptoms but is no longer detectable,” write the researchers. 

Ultimately, neither study is able to solve the riddle of what caused the illness. However, the authors of the second paper say that “if a directed energy “attack” is truly involved, it seems to create symptoms without persistent or detectable physiologic changes.”

The two studies have been published in the Journal of the American Medical Association.