An 81-year-old man from Bath baffled doctors when he came round after a stroke – and started speaking Welsh.
Alun Morgan, from Bathwick, was also amazed when he began speaking in a language which he had not heard since being evacuated to Wales as a child in the war.
Morgan suffered from aphasia that affected his ability to speak. Did the English part of his memory access shut down and all he could access was the parts that recalled Welsh? Amazing.
What do you know! I found a blog post on this.
Foreign Language Syndrome
Neuroscientists are still trying to make sense of all this. One proposal is that in polyglots, while speaking one language, the other language(s) have to be inhibited. If this ability to inhibit one language is impaired, then this will result in involuntary switching or mixing up the languages. It is further proposed that some patients with aphasia may have the inability to turn off the inhibition of one language – so the language may still be there, but permanently inhibited and unavailable. Such cases are rare but provide a window into the organization of multiple languages in the brain.