Scientists at the University of Pennsylvania noticed the whole white matter volume – areas of the central nervous system that affects learning – of the diplomats was roughly five per cent smaller than usual.
Meanwhile the functional connectivity in the auditory network was down approximately 15 per cent.
Dr Douglas Smith, who took part in the analysis, likened the neurological effects on some of the patients as an “electricity brown-out”.
“These types of changes are completely unknown to us,” he told The Daily Telegraph.
“We haven’t seen anything like it before and it’s very curious. What it is, we’re not sure, but there does appear to be something there.”
Dr Smith disclosed that while some of the patients have recovered, others still struggling with their symptoms.
The acoustic weapon theory gained further currency when an audio recording of a persistent, high-pitched drone sound was made by US personnel in Cuba and passed to the press in 2017.
But a fresh analysis published earlier this year suggested the din was the result of the Indies short-tailed cricket.
Prof Jon Stone, an NHS consultant neurologist and researcher at the University of Edinburgh, said: “A whole range of conditions such as those causing chronic dizziness, migraine or even depression will tend to show changes in the brain in these types of studies in comparison to healthy controls, since all those conditions arise from the brain.