An independent analysis of the brain of diplomat Mark Lenzi has found that the 2017 so-called “sonic attack” on the US diplomat in China has impacted at least 20 regions of his brain, but a cause of the damage has still not been determined.

Mr Lenzi was stationed in Guanzhou when he began experience unexplained symptoms including a headache, memory problems, difficulty reading, and sleep issues.

The new analysis, according to doctors, has determined through MRI that roughly 20 regions of the brain have “abnormally low” volumes of function, including areas that involve emotion, motor skills, and memory function.

The doctors, in announcing the results of the study into around 170 regions of Mr Lenzi’s brain, found that at least three regions had higher than usual activity.

They said that the lower levels of brain activity could indicate brain damage, and that the higher activity in other areas could indicate that other parts of the brain have compensated.

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The so-called “sonic attack” on Mr Lenzi came amid a string of similar affronts, which included apparent attacks on diplomats who were then living in Havana, Cuba, and brought back to the United States amid the bizarre conditions.

The cause, though, has not been determined in the odd affair.

“There's no smoking gun,” said Dr Edward Soll, the medical director of The Concussion Group, which conducted the testing, according to CNN.

Mr Soll noted that the evidence does suggest something happened, even if he and his fellow researchers cannot be sure what happened. “It would be hard not to conclude that there was serious damage to this gentleman's brain.”

The sonic attacks were first reported among diplomats in Cuba in 2016, and the US State Department has since confirmed similar attacks in China

Those diplomatic workers then described hearing odd sounds, including buzzing and grinding, before experiencing symptoms. Previous studies have likewise indicated that the brains of those impacted have shown divergence from those of healthy humans, though nobody has come up with a plausible scenario for how the attacks were carried out.