Julie Matthias’s family have a game they sometimes like to play after she comes home, disappointed, from another doctor’s appointment. During dinner, they pick a foreign accent, and challenge each other to speak in the strange voice.

The playful jokes help to distract from the distress of a condition that her doctors have struggled to treat. Despite having lived in the UK her whole life, Matthias suddenly found that she no longer speaks with an English accent – sounding French or Chinese instead. “Four years ago this Easter – that was the last time I heard my own voice,” she tells me on the phone.

Matthias is one of a handful of people in the UK with foreign accent syndrome. Although their speech is completely fluent, their voices have somehow taken on odd characteristics that make them sound as if they grew up in another country.

The causes are complicated, and sometimes puzzling to scientists. Matthias thinks her experience can be pinned down to a car accident that was followed by blinding migraines, often accompanied by debilitating body pain. “It feels like your brain is going to explode,” says Matthias. “Your joints are so tender, so painful, you feel you can’t breathe, you can’t get the air in… I’d rather have more babies than go through that pain again.”

Hear Julie Matthias’s accent in an interview with BBC News

Then, a few months after these painful episodes started, something even stranger happened. Her voice started shifting accent. The change soon caught the attention of people in her beauty salon. “Clients talked to me as if I didn’t understand English.”

It’s not clear exactly why the car accident caused that shift. Despite ongoing hospital visits, no neurologist has yet been able to pin down a definite cause of her migraines or her strange accent. It is especially hurtful, she says, when people assume the lack of diagnosis means her condition is imaginary, or they fail to see the impact of the disorder. “People just take it as a joke condition. They focus on the fact that we speak with a [funny] accent.”

It is no laughing matter. “Think: you go to sleep, wake up and no longer sound to you like the person you really are –and there’s nothing you can do about it,” says Sheila Blumstein at Brown University, Rhode Island. “That has a very profound effect on the patients.” Fortunately, researchers like Blumstein are now coming to terms with both the causes and strange consequences of this puzzling disorder.

Initially, even the nature of the altered voice was a mystery. Were the people speaking with genuinely foreign accents – or were we being fooled by some other change? Blumstein’s early work showed that the vowel sounds do indeed change a little, but more often it’s down to differences in the underlying music of the voice. “When we speak, we have a speech melody and rhythm – and it’s here they have changes,” says Blumstein.

The voice’s intonation and stress – including the subtle ways we embellish a sentence and emphasise our point – is central to this. In 2012, Anja Kuschmann at the University of Strathclyde in Glasgow found subtle differences in the way people with foreign accent syndrome highlight different words. “They still use the same rising and falling tones as healthy speakers – but they use a lot more of them. Instead of highlighting some of the words, they highlighted all of them.”

Intonation is one of the hardest aspects of an accent to master – many foreigners do indeed have abnormal voice rhythms compared to native speakers. Even so, the perception of the specific accent is somewhat subjective; some may think a subject with foreign accent syndrome sounds Russian; another, German. Indeed, what you hear in their voice probably depends on your own expectations. “It’s a fiction created by the listener,” says Johan Verhoeven at City University London.

As I speak to Matthias, it is easy to see why these mistakes happen. She pronounces “accent” with a heavier emphasis on the second syllable, for instance, that reminded me of my French teacher at school. But her staccato rhythm might sound a little like a Chinese accent too.

Often, those subtle signatures can be traced to known neurological damage. For instance, Barbara Tomasino, who is based at the University of Udine in Italy, recently examined a patient with a brain tumour. “Sometimes she sounded like she was South American, sometimes she spoke with an English accent – it was a very strange way of speaking Italian,” says Tomasino. The patient was awake while a surgeon operated on the tumour, allowing researchers to probe the electrical activity and function of the cells around the cancer. Although it sounds painful, this is a standard procedure that helps the surgeon work out where the tumour ends. Combined with information from fMRI scans, watching the neural activity in this way also allowed them to detect the cells involved in controlling the mouth and larynx– which turned out to be right next to the site of the tumour. By pressing on that region, the tumour may therefore have been disrupting her ability to plan the complex tongue and move movements needed to talk normally – leading to her strange accent.

The patient continued speaking throughout the operation, to be sure the surgeon didn’t damage those vital areas surrounding the tumour. Although there was no immediate change in accent, as her brain recovered over the coming weeks, the patient found that her old voice had returned. “The latest news we have is that she’s OK and living normally,” says Tomasino.

Given that success, you might therefore expect all patients to show damage in that same part of the brain. Yet that’s not the case. “We’ve made great strides but we don’t know the whole answer,” says Blumstein. Perhaps a constellation of brain regions is involved, and if any one of them is damaged it can result in a different accent. One of Blumstein’s patients developed a foreign accent after one stroke – and when a second stroke damaged a separate, seemingly unconnected region called the cerebellum (a small, cauliflower-shaped node at the base of the brain), she was cured and started speak like normal. “I don’t know why it had the effect – other than that the cerebellum is in an area involved in rhythm,” says Blumstein.

In Matthias’s case, doctors have been unable to pin it down the biological cause. In many other ways, however, her experiences resemble those of others with the disorder – including a sadly altered perception of herself. “It takes away your whole identity – you lose what was you,” says Matthias. At one point, she was even afraid of seeing her own reflection. “It was hard to look in mirror and speak – because it wasn’t my voice.”

That’s not surprising, given the role the voice plays in forging our place in the world. “The way we speak is a window onto our inner self,” explains Nick Miller at Newcastle University. “It marks social class, education level, whether you come from this place or that place – so consciously or subconsciously, we use accent to portray who we are and how we are.”

Miller, along with Jack Ryalls of the University of Central Florida, recently compiled a book detailing these experiences, called Foreign Accent Syndromes: The stories people have to tell. The altered sense of self was familiar to many of the people who contributed their stories. “I feel so lonely, isolated, scared. I feel like I have bereaved a good friend,” wrote one contributor, Kath Lockett. Alone at home with her cocker spaniels, she had the eerie feeling that there was a “stranger in the house” whenever she spoke.

Compounding the issues with their identity, these people also have to deal with surprising, and sometimes unkind, responses from those around them. Accents are also an important way for us to form boundaries between different social groups. Accordingly, some of the people in Miller’s book report feeling marginalised – like “a foreigner in my own country”, he says. Matthias and Lockett have even experienced racism. “I had a taxi driver try to charge me double fare for a journey I have taken before,” wrote Lockett. “Two bus drivers treated me like I was deaf, stupid and belittled me.” Even friends can sometimes start to feel suspicious of their new vocal identity.

For Matthias, her own family have been the greatest comfort. “I don’t do sympathy very well,” she says. “My family know that, so they tend to take the mickey and ask me to say different words that I found difficult. We all sit around and laugh about it.”

Like many others with the condition, she tries to keep a positive attitude. “We try to look on the bright side, and things could be worse. My condition as we know it – and we don’t know a lot – is not life threatening. That’s what we’ve got to be thankful for,” she says. “You just have to learn to cope – to keep fighting every day.”

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