In 1941, in the height of World War II, a Norwegian woman named Astrid was hit in the brain with shrapnel during a raid. Two years later she met with the neurologist Georg Herman Monrad-Krohn, who noticed right away that despite her fluent Norwegian, she had “such a decided foreign accent that I took her for German or French,” he wrote.

He wasn’t the only one to make that mistake. The Germans had been occupying Norway since 1940, and though Astrid had never been out of the country, her accent made her seem like the opposition to her neighbors.

“She complained bitterly of constantly being taken for a German in the shops, where consequently the assistants would sell her nothing,” Monrad-Krohn wrote.

Astrid was not the first-ever recorded case of foreign-accent syndrome (that would be a Parisian man who developed an Alsatian accent after a stroke, a case first presented in 1907), but her case study was particularly detailed. Monrad-Krohn called her condition “dysprosody,” prosody being the elements of language other than the actual words being spoken (intonation, rhythm, stress, etc.). Astrid still had prosody—that is, her speech was not monotonous—but it was different than that of a typical Norwegian speaker.

The term “foreign-accent syndrome” was coined in 1982 by the neurolinguist Harry Whitaker, and it is, admittedly, a lot clearer than “dysprosody.” It’s a rare condition, but an interesting one, and there have been more than 100 case studies published. The most recent appeared in Case Reports in Psychiatry this year.

“The patient was a 34-year-old African American U.S.-born single female,” the report begins. She was brought to the psychiatry emergency room after assaulting her mother’s landlady, who she believed had cursed her using voodoo. Her family had a history of schizophrenia, and she was diagnosed with the condition herself upon this visit. She also spoke with a British accent. “She substituted ‘th’ for ‘f’ and ‘w’ for ‘wh’ as well as ‘t’ for ‘d’ and ‘ai’ for ‘ei,’” the researchers write. Unlike Astrid, though, she spoke in a bit of a monotone.

She refused medication, continued to have homicidal ideations toward her mother’s landlady, and eventually was transferred to long-term inpatient care. The researchers plan to follow up with the inpatient facility to see if it ever reverts back to American.

Astrid and this new patient represent the two different types of foreign-accent syndrome that have been reported—neurogenic and psychogenic. Neurogenic foreign-accent syndrome is more common, and comes after someone’s brain has been damaged, either through a stroke or from traumatic brain injury. Exactly how this leads to changed speech is unclear, but the damage is often located in the middle cerebral artery and brain regions associated with speech, especially in the left hemisphere.

In psychogenic foreign-accent syndrome, there isn’t any identifiable brain damage, but the person has some kind of psychiatric disorder, such as schizophrenia, or bipolar disorder, or conversion disorder, as well as the accent. “In the cases of psychosis, the new accent persists throughout the entire episode and may disappear after the psychotic episode subsides,” the researchers write. The patient in their study had a history of losing the accent after a psychotic episode had passed, though they didn’t observe that during her stay in the hospital. They also note that only recently has it been discovered that foreign accent syndrome can be psychogenic.

There’s also a mixed type of foreign-accent syndrome, which may have some neurogenic and some psychogenic characteristics.

There’s a ton of variability in how the syndrome presents—people can have changes in various aspects of prosody. Different listeners may hear different accents when the same person speaks (recall that Monrad-Krohn thought at first that Astrid was speaking with a “German or French” accent), or they may detect hints of the person’s original accent flickering under the new one. Patients may also have trouble putting sentences together, or may stress the wrong words or syllables.

Foreign-accent syndrome is similar to aphasia, a communication disorder that can cause a variety of speech problems, often after a stroke or brain injury. But that doesn’t explain psychogenic foreign-accent syndrome. And, if patients’ speech is just impaired, why would that register as a different accent?

In 2013, Lyndsey Nickels, a professor of cognitive science at Macquarie University, explained the phenomenon in The Conversation, using a highly-covered case  in which an Australian woman named Leanne Rowe woke up sounding French after a car accident. “Vowels are very susceptible,” she wrote, to being distorted by slight differences in tongue, lip, or jaw placement. “Different languages have different vowels, and within a language one of the main differences between accents is in the vowels.” It may be that the speech changes brought on by brain injury, or by psychiatric problems, are just familiar enough to remind us of accents.