People heard a mysterious noise, then experienced a variety of neurological symptoms.

University of Pennsylvania researchers studied that troubling pattern among U.S. government employees stationed in Cuba earlier this year, and now they are evaluating a similar scenario among others stationed in China, the Associated Press reports.

The Cuba incidents sparked concerns that the employees had been targeted with some novel sort of sonic attack, and similar reports this week in Guangzhou, China, have prompted several evacuations of diplomats and family members.

The Penn team, which published its Cuba findings February in the Journal of the American Medical Association, was not able to prove what caused the symptoms in those patients. But after subjecting 21 people to a battery of tests, the authors said they appeared to have suffered "injury to widespread brain networks" despite having no history of head trauma.

"It appears that we have identified a new syndrome that may have important public health implications," senior author Douglas H. Smith, director of Penn's Center for Brain Injury and Repair, said at the time.

Asked about the reported China incidents, Penn Medicine said it could not reveal results of any patient evaluations.

"We are continuing to work with the Department of State to evaluate and treat personnel who have reported audible phenomena experiences," according to a health system statement. "We are not able to provide specifics about different patient groups at this time."

The 21 patients who were stationed in Cuba were found to have symptoms such as dizziness, headache, loss of balance, and memory problems, the Penn researchers reported in February.

Eighteen of them reported hearing an intense sound before the onset of symptoms; some also reported feeling unusual vibrations, such as the sensation in a moving car when the windows are partly rolled down.

"The good news is that the symptoms appear to respond to rehabilitation interventions in a similar fashion as we see in patients with persisting symptoms following a concussion," said the study's lead author, Randel Swanson, an assistant professor of physical medicine and rehabilitation.