A recent American study has revealed that a group of US diplomats stationed in Cuba suffered neurological problems during their time in the country. Studies of the individuals suggested they had concussion like symptoms but, did not have any records of trauma to the head.

The issue has become a cause for concern, with American officials claiming that Cuban forces staged sonic attacks on the diplomats. The claims have been denied, with local agencies pointing out that they did not have the means to carry out an attack of the kind that could cause damage from a long distance.

Researchers from both countries are still unable to identify any plausible cause of the brain damage. The Journal of the American Medical Association (JAMA) published a preliminary study on 15 February that involved examination results of 21 embassy employees.

18 individuals claimed that in 2016, they heard loud noises at their homes and hotel rooms. The sounds ranged from those of grinding metal, squeaks, buzzing and humming along with vibrations. Immediately after, they complained of headache, pain in one ear and loss of hearing.

In the days immediately after, other symptoms emerged — memory problems, mood swings, fatigue, recurrent headaches and an inability to concentrate.

The US State Department employed a team from the University of Pennsylvania to look into the matter.

"Uniformly, everyone who saw these patients was absolutely convinced," Dr Douglas H Smith, director of the Center for Brain Injury and Repair at the University of Pennsylvania, noted. "It looked like concussion pathology. Processing speed, inability to remember — those are such classic symptoms we see in concussion.

"We all believe this is a real syndrome. This is concussion without blunt head trauma," he added.

Despite being able to identify the medical issue, the team is still looking into possible reasons for the damage.

"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 from a directional exposure of undetermined etiology," the study's authors wrote.

They believe that a sonic blast could not have caused the problems but are considering other harmful energies like low-frequency infrasound, high-frequency ultrasound and microwaves.