As Fear shouts while watching a dream, 'Boo! Pick a plot line!' This often creates a disjointed narrative. In Pixar's film, Riley's mind has a studio called 'Dream Production' that creates movies based on her past experiences. Our brain tries to make sense of our thoughts by stitching them together into a logical story. REM sleep often includes dreaming, and one theory for why we dream is that the sensations and emotions we experience are a side-effect of random firing of impulses during the strengthening and pruning of the connections between neuron branches. In reality, we fall into non-REM first, then alternate between REM and non-REM over 4-5 sleep cycles during the night. In Inside Out, Riley enters REM (rapid-eye movement) sleep the second she closes her eyes. The brain's hypothalamus – located above the amygdala – controls the switch between being awake or asleep. Sleep is an important process for learning and storing memories. (An adult brain has 86 billion neurons, each with about a thousand synapses.) The pattern of nerve impulses across the cerebral cortex creates the physical trace of a memory, what scientists call an 'engram'. More precisely, each memory is stored or 'encoded' as a pattern of synapses, as the tiny gaps between brain cells. But in the brain, each memory doesn't exist in a specific location, but as a branching network of neurons. In the movie, an individual memory is a single orb. Jellybean-like characters known as 'Mind Workers' pick memories off a shelf and thrown them into the 'Memory Dump', a deep chasm where the unwanted orbs go dull and the information they carry – such as old phone numbers and piano lessons – is soon forgotten. From above, Long Term looks like the cerebral cortex, folded outer layers that make a mammal's brain to resemble a walnut. The memory orbs of Inside Out are sent through vacuum tubes down to 'Long Term', a library of endless shelves that hold Riley's memories. Long-term memory in Inside Out (Image: Disney/Pixar) 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. 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'. 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. 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'). 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. 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.

Robert plutchik's wheel of emotions