This means McKinnon can’t experience the nostalgia of reliving the best times in life – but the upside is that she can’t recall the pain associated with the bad things either. Something difficult like the death of a family member feels just as intense at the time, but the feeling soon fades. And it could make her a nicer person too. She doesn’t hold grudges, because she can’t conjure up the emotion that made her feel bad in the first place.

As for the cause, so far researchers can’t find any disease or injury associated with the condition and have to conclude that people are probably born with it. But Levine and his team are studying possible links with other conditions.

McKinnon also has aphantasia, which means she can’t picture images. (Find out more about aphantasia and the people whose minds are ‘blind’). Is this preventing her from holding rich recollections of events in mind, compared to other people? It’s hard to know for sure. Decades of memory research have shown that we reconstruct an event in our minds each time we recall it – but we don’t know if we all do this in the same way. Some people might see an image or video in the mind’s eye; others might think more in terms of abstract ideas or facts.

Catherine Loveday, professor of cognitive neuroscience at the University of Westminster, wonders whether there are parallels with our memory of very early life. We are able to describe events that happened to us before the age of three, because we might have heard a lot about them or seen photos. But we find it difficult to recall what the experience felt like.