The Pentagon is backing animal experimentation in an attempt to determine the cause of the mysterious “Havana Syndrome” that has afflicted scores of U.S. diplomats, intelligence officers, and other government personnel abroad, according to a Thursday report from Politico. The testing primarily involves using radio frequency waves to see if similar unexplained symptoms as have been reported—including headaches, nausea, and cognitive difficulties—arise in the animal subjects, according to public documents and three people familiar with the matter who spoke with Politico. In September, the U.S. military granted Michigan’s Wayne State University $750,000 to test the waves on ferrets, information on the grant posted online shows. A spokesperson for the department confirmed the grant, saying the tests would “mimic mild concussive head injury” in animals in an attempt to “determine if the model is comparable to the abnormalities seen in humans following concussive head injury.” Two unnamed officials also told Politico that pulsed radio frequency was being tested on primates with a similar aim. The department spokesperson declined to comment on those experiments.