What’s your earliest memory? Chances are you can’t remember anything before the age of three. Otherwise known as childhood amnesia, it affects us all but isn’t quite the stuff of Hollywood. In the movies, the plot usually revolves around someone being bopped on the head and suddenly having no idea who they are or what they are supposed to be doing. And more often than not, a second whack to the head and the person’s memories return, good as new. But is that an accurate depiction of amnesia?

I can’t remember anything that happened before two weeks ago… I don’t know who I am, I don’t know where I’m going, none of it. Matt Damon as Jason Bourne

Whether the Bourne Identity, Memento, 50 First Dates or Hitchcock’s Spellbound, there are plenty of movies that depict extreme cases of amnesia. In real life, cases like these aren’t nearly as common or black-and-white as Hollywood might have us believe. But there are a variety of real types of amnesia, some more common than others.

What do Jason Bourne, Dory and ‘forgetful’ Lucy Whitmore have in common? Amnesia.

Childhood amnesia

Few people can remember anything from their childhoods earlier than age three. Despite some people claiming otherwise, research suggests that people aren’t able to remember their own births.

Why can’t we remember specific events from early in our lives? We certainly don’t forget skills like walking, talking and riding a bike we learn during those first few years. Sigmund Freud suggested we suppress these early memories because they were sexual and traumatic.

A more recent theory suggests childhood amnesia is a result of lack of language. It turns out that if children don’t have the necessary vocabulary to describe an event when it happens, they aren’t able to describe it later, even after learning the necessary words.

New research suggests that we forget our early years because of the fact so many new brain cells are being formed in the hippocampus, which is an important brain structure involved in memory formation. Essentially, the new brain nerve cells disrupt the circuits (and memories) that have already been formed in our brains.

Who are you?

Retrograde amnesia is when all memories formed before a particular event – like a brain injury – are lost. Scientists have been fascinated by this kind of amnesia for more than 120 years and have studied many patients affected by it.

In one case, a woman, known as G.H. woke up after surgery performed in August 2002. She was convinced it was May 1989 and was unable to recognise her own children. G. H. couldn’t remember anything about her previous life after May 1989.

Excitingly, research published earlier this year showed that the lost memories may in fact still be intact in the brain, but access to the memories has become blocked because of disease or trauma. The researchers found particular cells called Engram cells retained the memories and the memories could be recalled by shining a light on the cells. I should point out that unlike in the movies, there is no evidence that a second ‘hit’ to the brain brings back the lost memories.

Just keep swimming

Remember Dory in the movie Finding Nemo? And Leonard Shelby (Guy Pearce) in Memento? These are two of the more accurate movie portrayals of amnesia, in both cases, anterograde amnesia.

People suffering anterograde amnesia retain their identity and memories of their lives before a particular event (like a head injury) but completely lose the ability to form new memories. In Memento, Shelby is shown tattooing facts about his wife’s murder onto his body as the only way to be able to hold onto them.

We understand stacks about this type of amnesia because of a famous patient known as Henry M. Henry’s amnesia was the result of brain surgery performed to try to reduce his epileptic seizures. The surgery removed a number of areas of his brain tissue and left him with no memories of anything that happened to him after the surgery and the inability to retain any new information for more than a few minutes. Henry M’s amnesia has been studied extensively and is fascinating to read about.

Play it again, Sam

And then there are many more complex and fascinating examples of amnesia.

For example, there was a professional cellist who developed severe amnesia after suffering a viral infection of the brain. He was unable to recall any events from his past life, or remember any of his friends or family. He also had difficulty forming new memories. But he could still remember and play every piece of music he had ever learned, sight-read new music and learn new music he had never heard before.

And there was even one documented case of amnesia just like in the 2004 film 50 First Dates. As a result of a car accident in 2005, a patient known as F.L. wasn’t able to retain memories from one day to the next. During any one day her memory was normal but her memory of each day disappeared during a night of sleep. But in a fascinating twist, subsequent research suggested her own experience of amnesia may have been unconsciously influenced by her knowledge of how amnesia had been depicted in the movie. When she didn’t realise she was being tested on something she had learned prior to that day, her memory was quite good. Drew Barrymore happened to be her favourite actress and with time and treatment, her amnesia improved.

Now if that’s not life imitating ‘art’, I don’t know what is.

Links and stuff

• The Atlantic: Amnesia and the self that remains when memory is lost

• Scientific American: Why can’t you remember being a baby?

• Video by Crash Course Psychology: How we make memories

• The New Yorker: The man who forgot everything, about Henry Gustave Molaison

Radio on demand

This post accompanies a radio segment on Triple R’s Breakfasters program on Wednesday 1 July 2015.