Have you ever wondered how your memory works? Where it is in your brain? How memories are made? All will be explained, with a little help from the film Inside Out.

Inside Out is one of the most imaginative films in Pixar’s catalogue. The stage is inside the brain of a girl called Riley and the characters are her emotions – Joy, Sadness, Anger, Fear, and Disgust. The plot revolves around retrieving important ‘core memories’ that have been lost. Memories are represented as globes stacked on shelves in the brain, tinted by colours that match those of the accompanying emotions.

How accurate is this depiction of memory? It turns out Inside Out is a lot more reliable than you might think.

In the brain, memories are thought to be initially stored in the hippocampus – a small, curved region located deep within the brain, just above the level of the ear on each side. The surrounding regions also contribute to memory. Over time, some of these ‘short-term’ memories become ‘long-term memories’, which are stored as connections with the cerebral cortex (the large, outer layer of the brain).

When Riley goes to sleep, Joy watches as the memories rattle out of their initial storage in headquarters and are flung across the night sky like shooting stars. They streak down and land across a vast landscape of dense curves and folds. It’s a clever and stylish representation of the storage of the memories across the cerebral cortex. This moment in the film is an amalgamation of several different processes in the brain, so it’s worth unpicking these.

The temporary storage of facts in working memory only lasts up to 30 seconds. The transfer to long-term memory happens almost immediately, not during sleep as the film shows. 

There is a role for sleep and dreams in memory, but this is actually in the consolidation of long-term memories. A better representation of this phenomenon in the film would be if the globes in long-term memory were to glow brighter and become organised, so that related memories are stored together. 

One of the other main features of the film is how the memories are entwined with the emotions. This is well-established in psychology – the emotions affect how we record memories, but also how we remember them. It is much easier to recall memories from your life that matches your mood, and we tend to find positive memories easier to remember than negative ones as a rule. 

Finally, onto the substance of the memories themselves. Unlike in the film, these are not stored as a single ‘video clip’ – the information from our senses is stored in different regions of the brain, so that we can recall what someone said or what they looked like when they were saying it, or both at the same time.

The fundamental unit of memory is called an engram – the group of connected neurons that encode a single ‘unit’ of information. The hypothesis of an engram has been around since the 1920s, but in the last two decades we have been able to directly observe these neurons and manipulate them. In one such experiment in 2012, researchers were able to directly induce recall of a memory. Using a technique called optogenetics, they activated a population of neurons in mice which had been active during learning of a fear response, causing the mice to ‘remember’ the fear response and freeze. 

Overall, the view of the human memory we get from Inside Out is not one from the inside out, but from the top down. A little more research is needed for the curious viewer to find out exactly what makes up a memory. This is no criticism of the film, though – Pixar can hardly be blamed for not animating an engram. It succeeds in capturing lots of important concepts about the human memory without ever feeling didactic, conveying them not with words but with images. And, best of all, the science is being used to tell a story. What setting for a story could possibly be as interesting as the human brain?

Image credit: Jetiveri/ Pixabay

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