The last great mystery of the mind: meet the people who have unusual – or non-existent – inner voices

Does your internal monologue play out on a television, in an attic, as a bickering Italian couple - or is it entirely, blissfully silent?

Claudia*, a sailor from Lichfield in her late 30s, is not Italian. She has never been to Italy. She has no Italian family or friends. And she has no idea why a belligerent Italian couple have taken over her inner voice, duking it out in Claudia's brain while she sits back and listens.

I have no idea where this has come from," says Claudia, apologetically. It's probably offensive to Italians." The couple are like the family in the Dolmio pasta sauce adverts: flamboyant, portly, prone to waving their hands and shouting. If Claudia has a big decision to make in her life, the Italians take over.