It has been 15 years since Catherine Tate’s fan-favourite Donna Noble left Doctor Who. Perhaps you remember it like it was only yesterday, which is something that can’t be said for Donna herself. David Tennant’s Doctor was forced to erase her memories of their time together, lest her puny human brain burn out from too much Time Lord knowledge. You may be shocked to hear, however, that there are doubts over Doctor Who’s scientific rigour.
“We don’t know the ultimate capacity for human memory,” says neuroscientist Dr Dean Burnett, author of Emotional Ignorance: Lost and Found in the Science of Emotion.
“No one’s lived long enough to fill it, for a start. If you did replicate the human senses in a computer and stored everything that you got from a live feed, it would fill up a hard drive pretty quickly. But that’s not how memories work. We don’t remember every single element of every experience we have of every waking moment. Our brains are a lot more discrete.”
Nevertheless, the idea of wiping someone’s memory isn’t entirely implausible, points out Burnett.
“I think if you ran a powerful enough electric current through the main storage regions of the brain, then that would scramble things,” he says. “How you would do that safely – to the point where you don’t lose vital memories, or the ability to remember new things – is another matter though.”
The idea that you can eliminate specific memories – à la the Doctor – is a far more fantastical concept, however.
“We can’t look at someone’s brain and say, ‘Okay, here’s a memory of when they got their first bike’,” says Burnett.
“The best we could do is to look at someone’s brain in a scanner to see what parts are activated when they think of that bike. And even then it’s tricky because your frontal lobe, which is retrieving the memory, will be active, but there’ll be lots of different parts of the brain being triggered simultaneously too.
"In one part may be the memory for ‘bike’, and in another part is ‘childhood, 1987’. The memory is not in one location. That’s why it’s so difficult.”
How a Time Lord could actually 'erase' your memories
Of course, if anyone could figure out how to isolate and erase specific memories, it would be a 900-year-old Time Lord. But Burnett has another theory: that the Doctor didn’t wipe Donna’s memories, he simply disrupted her ability to recall them.
“Even if the Doctor could sever memories, it would be an immensely fiddly process,” he says. “It would be easier and safer for him to put some kind of psychological block on those memories instead, to teach her brain that those memories are out of bounds.
"It’s almost like giving someone a traumatic association. People with PTSD tend to show avoidant behaviours. If there’s any possibility of encountering the cause of the trauma, they’ll actively avoid it, sometimes without realising. The brain takes over and does it itself.”
Burnett’s theory is supported by events in the 2009 episode The End of Time, where the sight of everyone on Earth turning into supervillain The Master triggers dormant memories (it’s a weird show).
“In the case of PTSD,” says Burnett, “if you’re exposed to triggers beyond your control, that could lead to those memories rushing back, because the brain’s block may not be enough to suppress them.”
The Doctor’s block will be tested again this November on BBC One, as Tennant and Tate reunite for a series of 60th-anniversary specials. Here’s hoping it’s a reunion to remember.
Read more:
- Doctor Who: Could regeneration really be possible?
- How Doctor Who's time machine measures up with real instruments of space and time
- Where do memories form and how do we know?
About our expert
Dean is a neuroscientist, author, blogger, occasional comedian and all-round ‘science guy’. He is the author of the popular Guardian Science blog Brain Flapping (now Brain Yapping on the Cosmic Shambles Network with accompanying podcast), the bestselling books The Idiot Brain and The Happy Brain, and his first book aimed at teens, Why Your Parents Are Driving You Up the Wall and What To Do About It.