Inside Out is not just Pixar's best film since Toy Story 3, it's also the smartest. Mostly set inside the mind of 11-year-old Riley as she moves to a new town, the movie uses colorful characters to illustrate how emotions influence our memories.
We humans have two main memory systems: implicit and explicit. Implicit memory includes unconscious processes like emotional and skeletal responses, learning skills and habits, plus reflex actions. Explicit memory stores facts and events, and recalling that information requires conscious awareness. The two systems can be separate, which is why you might retain an implicit fear of clowns after forgetting the explicit experience that originally triggered your coulrophobia. The two memory systems can also be connected when events have emotional significance – the focus of Pixar's film.
Inside Out depicts five emotions as characters with distinct personalities: Joy, Fear, Disgust, Anger and Sadness. These are inspired by the work of American psychologist Robert Plutchik, who proposed that we have eight basic emotions, which can be arranged on a wheel with pairs of opposites: joy and sadness, anger and fear, trust and disgust, anticipation and surprise.
Plutchik called this idea a 'psycho-evolutionary synthesis' because it's based on Charles Darwin's theory that an animal's outward expressions reflect emotions that help them survive. As stated at the start of Inside Out, fear stops you from putting yourself in danger, for example, while disgust prevents you from poisoning yourself. Although the film's major characters are Joy and Sadness, the most vital emotion in nature is fear. Having emotions is driven by natural selection: if an animal isn't able to recognise a potential threat, it risks being killed.
Learning and memory helps animals respond quickly to situations that resemble past experiences, which improves its chances of survival. Attaching emotions to an event gives that explicit memory some context, and also makes it stronger. As Riley's imaginary friend Bing Bong says, "When Riley doesn't care about memories, they fade."
In Inside Out, each memory is a glowing orb whose colours match the movie's five emotions: yellow for joy, blue for sadness, red for anger, purple for fear, and green for disgust. Memories aren't limited to a single emotion, as shown at the end of the film when most of Riley's memory orbs aren't uniform, but become marbles filled with multicoloured swirls of emotions. For example, while not named in the movie, combining joy and sadness (blue and yellow) creates sentimental feelings for the past, or nostalgia (Greek for 'ache for home').
Inside the brain
So how do memories and emotions become connected? The process begins with stress hormones released by adrenal glands, which ultimately activate the amygdala, a pair of tonsil-sized areas in each brain hemisphere. The amygdala is located above a pair of seahorse-shaped structures called the hippocampus, which is roughly equivalent to Inside Out's aptly-named 'Headquarters'. The five emotions personify the amygdala, and attach emotional significance to a new memory by pressing a big button on the control console in Headquarters, which is akin to nerve cells (neurons) in the amygdala sending signals to the hippocampus.
Memory has two lifespans: working (or 'short-term') and long-term. Working memory keeps knowledge in mind for cognitive functions like learning and reasoning, enabling us to compare and contrast information. Long-term memory is needed when the brain is presented with more information than it can handle, such as when you're asked to memorise 10 words at once.
Long-term storage of facts and events (explicit memory) depends on the hippocampus, as proven by the case of 'HM', who suffered from epileptic seizures. In their famous 1957 study, surgeon William Scoville and neuroscientist Brenda Milner removed a small part of HM's brain, the hippocampus and surrounding areas within the medial temporal lobe. The procedure cured HM of epilepsy, but also left the patient with anterograde amnesia – the inability to form new long-term memories.