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updated 4/23/2010 12:41:48 PM ET 2010-04-23T16:41:48

After 24 hours in a coma, a Croatian girl woke up speaking only German, according to reports that spread across the Internet last week. The 13-year-old had been studying German in school and watching German television shows on her own, according to various versions of the story, but she was not fluent until after the incident. Meanwhile, she lost the ability to speak her native language.

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Discovery News did not confirm the report with the girl's doctors or parents, but experts say the story is plausible — to some extent.

In a condition called bilingual aphasia, people often lose one of their two languages because different parts of the brain are involved in remembering each one, explained Michael Paradis, a neurolinguist at McGill University in Montreal.

Even if a brain injury affected the Croatian teenager's memory of her native language, the brain areas that were learning German could have remained untouched.

"This has been observed thousands of times," Paradis said. "It's not surprising at all. I'd like to know all the facts, but it's quite possible that after a coma, you'd have problems which might be located in such a way in the brain that they affect one language but not another."

What can't be true, though, is the claim that the coma gave the girl fluency that she didn't have before.

"I looked on the Web and saw comments that she recovered perfect German," Paradis said. "This cannot be the case. If she recovered German to the point that she could communicate well, that's fine. That's the kind of thing you would expect."

Bilingual aphasia is possible because different types of memory are involved in learning first and second languages. As toddlers start to talk, their brains treat language like walking, jumping or any other motor skill. Those abilities belong to a realm called procedural memory; we do them without consciously thinking about them.

When an adult or older child learns a new language, on the other hand, something called declarative memory takes charge. As if the language were history, geography or math, the brain learns rules and memorizes facts. After years or decades of developing fluency, some of that knowledge gets transferred into the subconscious procedural memory. However, declarative, or conscious, memory will always hang on to it in some way. (Children who grow up multilingual can store more than one language within the subconscious memory system.)

Multiple areas of the brain intersect to encode both types of memory, but the two systems are generally distinct from each other. That makes it possible for a localized lesion, tumor or traumatic injury to wipe out one language but not another.

Native language likely to return when swelling shrinks
Paradis suspects that the Croatian teenager suffered from edema, or swelling, that interfered with her ability to speak Croatian but not German. In cases like hers, he said, the native language usually returns when swelling goes down after a few weeks or months.

Whether true or not, the case points out how much scientists still don't know about language and the brain.

"The bilingual neuroimaging literature is quite messy, and we're really only beginning to understand how the brain is capable of sustaining multiple languages," said Matt Leonard, a doctoral student in cognitive science at the University of California, San Diego.

Along with neuroscientist Eric Halgren and colleagues, his group is using new, magnetic field-based technology to zero in — in more detail than ever — on which parts of the brain process language and in what order.

"Second-language learning is a controversial field," Halgren added, with ongoing debate about which brain areas are involved. "The amount we don't know is far greater than the amount we know. That is going to be true for a long time."

© 2012 Discovery Channel

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