(CNN) Doctors shared details Thursday about what happened to the brain of one diplomat who may be a victim of the so-called sonic attacks that have impacted dozens of people in Cuba and China.

Researchers revealed the results of an independent brain analysis of Mark Lenzi, a US diplomat who was stationed in Guangzhou, China, in 2017 when he started experiencing unexplained symptoms including headache, difficulty reading, irritability, as well as memory and sleep problems.

Among the MRI findings: 20 brain regions with "abnormally low" volumes, including regions involved in memory, emotional regulation and motor skills that may correlate with Lenzi's symptoms, doctors said. Of the 107 regions they looked at, they also found three that had bigger volumes. They said the parts of the brain with low volume may reflect brain injury, and those with high volumes could be evidence that other parts of his brain have compensated.

These tests, however, do not reveal the cause. That remains a mystery.

"There's no smoking gun," said Dr. Edward Soll, medical director of The Concussion Group and a radiologist who was among those who evaluated Lenzi's brain scans. Still, looking at the compendium of evidence, "it would be hard not to conclude that there was serious damage to this gentleman's brain," he added.