A new study found key differences in the brains (particularly the cerebellum) of the diplomats that took part in the so-called Havana Incident. But don’t put your tinfoil hats just yet: the researchers found no sign of attack.

The Havana incident remains just as puzzling as before.

In 2016, an episode worthy of science fiction took place in Havana, Cuba. U.S. and Canadian diplomats (and their family members) experienced strange neurological symptoms, including headache, hearing loss, memory loss, and nausea. The symptoms always made themselves felt when the diplomats were at home or at a hotel, and they were often preceded by strange grating noises apparently coming from a specific direction.

To this day, it’s unclear what exactly happened. Given the sound-hearing symptom, some parts of the media were quick to speculate a sonic attack, although no evidence in favor of this was ever uncovered. To our knowledge, the technology needed to carry out such an attack is not readily available.

Others were quick to say that nothing really happened, and these symptoms could be attributed to fatigue or stress. But this also doesn’t seem to be the case.

At the request of the U.S. government, University of Pennsylvania researchers examined 21 affected diplomats. The preliminary results were published in the Journal of the American Medical Association in March 2018. The study concluded that “the diplomats appear to have sustained injury to widespread brain networks”, describing “a new syndrome in the diplomats that resembles persistent concussion.”

The study sparked more interest in the case, but it also raised criticism, particularly due to a lack of enough evidence to support this theory. Now, a new study analyzed fMRI images from the patients’ brains. They found statistically significant differences in brain volume, tissue properties, and connectivity between the patients and a healthy control group. These differences fit with the symptoms the patients described.

“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,” said lead author Ragini Verma at Penn University. “These differences persisted even when people with some history of brain injury were excluded from the analysis.”

The problem with this case is separating fact from fiction. The team stresses that there was no evidence of any attack whatsoever, but they do say that brain differences exist and they are significant.

“The cerebellar findings in this neuroimaging study are notable, given that a number of the patients evaluated exhibited abnormalities in balance and the coordinated movement of the eyes, both of which are associated with cerebellar dysfunction in the brain,” said study co-author Randel Swanson, DO, PhD, an assistant professor of Physical Medicine and Rehabilitation at Penn.

They even went as far as to say that there is evidence of a previously undescribed syndrome.

“These findings may represent something not seen before,” Smith said.

However, not everyone is convinced. In an editor’s note, JAMA senior editor Christopher Muth and executive editor Phil Fontanarosa cast doubt on the significance of these findings:

“Despite the differences in advanced neuroimaging metrics between patients and controls reported in this study, the clinical relevance of these differences is uncertain, and the exact nature of any potential exposure and the underlying etiology of the patients’ symptoms still remain unclear,” the editor’s note reads.

Furthermore, neuroscientist Douglas Fields, who has studied these events independently, told Gizmodo that the methods used in this study aren’t suitable for diagnosing a syndrome of any kind, let alone something we’ve never seen before. The authors themselves admit in the study that the “clinical importance of these differences” in the brain is uncertain.

All in all, there’s no evidence of any sort to support the idea of an attack — but there’s also no reason to believe that the patients are making their symptoms up. They seem to exhibit some neurological changes, but whether or not this is actually true, and the significance of these changes remains a matter to be cleared out in the future.

The study has been published in JAMA.