The Neuroscience of Disney Pixar’s Inside Out

Warning: Minor spoilers if you have not yet seen the movie!

Summary of Inside Out:

Inside Out is Disney Pixar’s latest film and is already making headlines, with a nearly perfect score on Rotten Tomatoes. Watching the film through the lens of a neuroscientist was very enjoyable. The film captivated many complex neuroscience topics and conveyed them for easy understanding for a general audience. I thought the movie was great and accurately (though not perfect) portrayed much of how the brain functions. This comes as no surprise as the film consulted with two well known psychologists, Paul Ekman and Dacher Keltner while making the film. There is a great interview with Dacher Keltner about Inside Out on ScienceFriday.com.

The movie follows a young girl named Riley from the day she is born till she is 12 years old. The film centers around five main Emotions in her brain which react to the world around her. Though there are many emotions, Inside Out settled on the five main emotions of Joy, Sadness, Disgust, Fear, and Anger.

Each emotion was its own animated character that could take influence of Riley via a control board. The control board began as a single button when Riley was a baby, and depending on which emotion touched it, that was the emotion Riley felt. With time the control board became more complex, with dozens of button, nobs, switches, dials, and even a socket for screwing in idea light bulbs (seen in the below picture). These emotions and control board reside in “Headquarters”, a fancy bubble looking room high above a deep, dark pit surrounded by a never ending plain of book shelf looking things for long term memory storage. Radiating out of headquarters, attached by what look like glass tubes, are Islands of Core Values floating above the pit. These islands are powered by Core Memories from Headquarters; memories so powerful and profound that they shape Riley’s personality. They range from when she was a little child and scored her first goal in hockey by slipping on the ice and accidentally hitting the puck into the goal past her goal keeping father (Riley loves hockey from this moment on) to memories of Honesty and Family.

As a memory researcher, the portrayal of memories and how they were handled was very interesting. Memories were depicted as spheres tinted a different color depending on their emotional context (above picture, left wall; yellow memories are for Joy, blue for Sadness, etc). Any of the five main Emotions or other workers in the brain could pick up a memory sphere and replay it. Memories could also be called up to Headquarters and replayed to Riley’s consciousness. Memories of the events of the day come into headquarters as they happen and are stored there for a short time. Each night, when Riley falls asleep, memories are sent out of Headquarters to long term storage. They are sucked out using a vacuum tube and sent out to the book shelves. Little workers depicted as blobs monitor the long term memory reserves and decommission faded memories. Faded memories are shown as grey spheres with little shine relative to robust memories. These faded memories are sent to the huge central pit where they eventually turn to dust. The little long term memory workers sometimes send up to Headquarters a memory of an annoying chewing gum commercial which gets inadvertently replayed over and over in Riley’s mind.

Enough of the plot, lets dive into the science.

What is Headquarters in Inside Out?

Dr. Steven Novella interprets in his blog post that Headquarters is suppose to be the seat of consciousness and goes on to say why this would not be the case. While I do agree Headquarters in the movie does not do a good job at portraying what consciousness likely is, which current research tells us is likely a very distributed process involving many brain regions rather than a central “headquarters”. I do not think Headquarters was meant to be consciousness. In the film, everything is not reliant on Headquarters and Riley can still operate without constant input from Headquarters. Headquarters instead seems to play a much more modulatory role in Riley, coloring her experiences with emotions, remembering events, recalling events, and inputting emotions into the control panel that then dictates how Riley reacts. Rather, Headquarters fits much more into the role of the limbic system (brain system thought to regulate emotions). Of course it is simplified for the film, but the core elements are there.

Headquarters, the hippocampus and memory formation:

The limbic system contains the hippocampus which is vital for the formation of episodic memories; memories that consist of a what, when, and where. The hippocampus is a deep structure in the brain shaped somewhat like a seahorse. As we see throughout the film, every time Riley experiences an event, a memory sphere of that event comes into Headquarters. This fits well with the current neuroscience research in many ways. Without a hippocampus the formation of new episodic memories is nearly impossible. One famous example of this is Patient H.M. who had his entire hippocampus removed due to severe seizures. The seizures stopped but HM was never able to form another episodic memory. Many researchers study the hippocampus in attempts to unravel the mechanisms which allow the hippocampus to form these complex memories.

Just like in the movie, the hippocampus/Headquarters does not store episodic memories forever. Once the hippocampus has formed an episodic memory, these memories then leave the hippocampus and are consolidated into other brain regions in the neocortex. Consolidation is the process of stabilizing a memory for long term storage.

A recent paper (PDF) from Mark Schnitzer’s lab at Stanford has been able to image this process of memories leaving the hippocampus. It is also known that sleep likely plays an important role in this consolidation process of memories leaving the hippocampus and being consolidated into neocortex (for review). These functions were portrayed beautifully in the film, with new episodic memories coming into headquarters as they happened but being physically sent out to other parts of the brain each night for consolidation and long term storage.

The brain’s memory replaying and the replaying of memory orbs:

The hippocampus is also thought to play a vital role in the recall of episodic memories, especially in the temporal order in which events happened. In the film, the Emotion characters are able to recall memories at Headquarters from long term storage and project the memories on a big screen. The memories would replay just like a movie being shown on a projector. These memories would then reach Riley’s consciousness and could influence her choices, or in the case of the annoying chewing gum commercial, make her hum the jingle. Indeed, when people recall memories to make decisions we can see increased activation in the hippocampus. The hippocampus, as put by Elenaor Maguire of University College London, is like our “mental time-space traveling machine”. Though the movie doesn’t explicitly depict Headquarters projecting forward in time, there is prospective time travel moments, like when Fear has to take into consideration every possible problem that can happen at the first day of school. This time travel function, both forward in time to possible events and backwards in time recalling memories, is a vital role for the hippocampus and in the movie, Headquarters.

Are memories really colored with emotions like Inside Out?

While the hippocampus likely plays a role in the emotional component of memories (one of my papers shows hippocampal representations of events are influenced by the emotional valence of the event), emotion can be found all over the brain. From the executive functioning, prefrontal cortical regions down to the amygdala, one of the oldest brain structures responsible for emotions. No matter where exactly specific emotions are regulated, the entire limbic system plays a vital role in them and in-particular attributing emotions to memories. Recent work out of MIT has shown it is possible to modulate the emotional context of a memory in mice by stimulating specific neurons in the hippocampus and amygdala. Researchers were first able to add a fear component to a once emotionless episodic memory of an environment. Recently the same group was able to reactive positive memories and decrease depression like behaviors. During Inside Out, if a Memory character touched a memory, the memory would take on that emotional context. This happened over and over with Sadness touching memories of Joy and “ruining” them. These seems to provide more evidence that Headquarters was more of the limbic system rather than consciousness.

Long term memory storage and forgetting:

Surrounding the central pit and Headquarters is a huge array of what resemble book shelves that house the memory spheres (pictured below). This is suppose to represent long term memory storage in our brains. Depicting long term memory storage like a vast series of bookshelves over a large area is quite accurate to how our brains store long term episodic memories. As talked about above, the hippocampus forms episodic memories but then sends them out to cortical regions for long term storage. Long term memories are stored all over the brain and usually in brain regions whose functions are related to the memory, for example the memory in mice for learning to press a lever for food is stored in the motor cortex.

Inside Out depicts the degradation of a long term memory as its loss of color and glow. Little workers come around and check memories on the shelves for their status. If memories are too degraded or the workers think the memories are not needed, they are sent off to the pit. In the pit we find possibly millions of old memory spheres, grey and dark. Some turn to a puff of dust. Forgetting in the brain is likely not this simple and it is not an easy thing to research. There are many competing theories on what forgetting is and it is possible they are all correct in some ways. Two main theories are Cue-dependent forgetting and trace decay.

In short, cue-dependent forgetting has its roots in more ethereal psychology but may have some merit. Cue-dependent forgetting is the failure to recall memories without a cue. In other words, without a cue that is associated with a memory, you are unable to recall the memory just by thinking about it. You may want to think back a few years ago to a specific event but you’re unable to do so. However, if your friend mentions something that happened during that event, a cue, then the memory rushes back. Rather than the memory being gone, it was simply hard to access.

Trace Decay Theory states the memory trace actually decays and is lost forever. This theory also dates back to 1914 well before current neuroscience techniques were available, it is possible to apply it to our current understanding of the brain. For short term memory, such as keeping a phone number in your head for a few seconds, this theory in its original form may have some merit. For application to long term memory storage, Trace Decay Theory has been renamed and repacked simply as Decay Theory. Memories are physically stored in spines on dendrites. It is possible for these spines to degrade and the connections they make to be lost. This is an important function in some respects, you would not want to keep in memory information that is wrong. However, these processes may also take place in spines that represents memories you’d like to keep. Inside Out seems to play on this theory of forgetting more than any of the other theories. Old memories, once in the pit, are lost forever. But, there is a hint of cue-dependent forgetting. By singing old songs (cues) with Riley’s imaginary friend, Joy is able to escape the pit with core memories in hand.

Are Inside Out memory spheres real?

In the name of story telling I can understand depicting memories as nice clean spheres. However, in the brain memories are not this nice. An entire memory, especially an episodic memory, involves many neurons across many brain regions all activating in a coordinated way. Researchers often call the physical representation of a memory an Engram. That is, all the cells and cell processes involved in a particular memory. We also know that the brain circuits that make up specific memories are very intermixed with other memories that share similar events. A single neuron may represent the same thing (contexts, objects, emotions) in different memories, as long as that thing is constant in the different memories.

Also, once memories are formed, new additions can be added to them later. Inside Out does show the emotional context of a memory sphere changing if a different emotion touches it. However, even more information can be added to it. For example, we have shown that if an engram of cells represent one object that is rewarded in a specific location, within a specific environmental context, if a new object is introduced that is different to the first object but is still rewarded in that location in that context, that first engram with represent the memories of the second object as well. We call these associations between memories Schemas. The hippocampus distinguishes memories by the environmental context in which they were experienced. Then the hippocampus associates similar memories together by where they occur within a context, the emotional valence of a memory, and finally similar objects. Brain regions with more complex, executive functions relate and distinguish memories primarily with more abstract elements, such as the value of an experience.

In the case of Inside Out, Riley may have a massive memory sphere for all things Hockey. Around this sphere could be rings or shapes like electron orbitals, that represent different memories of Hockey, there could be one for playing Hockey with her dad, another for playing Hockey with her School in Minnesota. Then, within these representations, all the specific memories of individual events are stored as memory spheres. Lastly, the rings/orbitals of different memories would be further apart for memories of Hockey that are very different, for example memories of San Francisco Hockey vs Minnesota Hockey. It could have been a nice touch for Inside Out to have subsequent memories related to a Core Memory travel to their Core Memory Island rather than to the normal long term memory storage.

Putting it all together, this gets a bit technical, but hopefully this figure makes things clear.

Lets pretend we have a little mouse. At the start (top left) the mouse has a bunch of cells waiting to encode information. First we put him in a blue box with blueberries. We let the mouse explore this new box and eat his blueberries. We can now see in his brain he has four new neurons encoding a the blue box. This is an engram forming the memory of the blue box experience. We take the mouse out, let him rest of 5 minutes, then put him into an orange box with orange slices to eat. If we look into his brain some things are changing. Two of the blue neurons now also encode some elements of the orange box, say the first one encodes the shape of the environment (square box) and neuron further to the right encodes the time these experiences took place, both on the same day. This is an example of an associative schema that links together memories that are similar. We also have a new purely orange neuron, encoding the novelty of the orange box with orange slices. Next, we take out the mouse, wait 5 minutes, and put him in a green cylinder with kiwi fruit. We can see three new neurons encode the new green environment, it is a different shape and size, new color, and has a new food. But, the time encoding cell that keeps events associated in time encodes the green cylinder too. Next we let the mouse hang out at his house for three weeks. Then we put him in a blue cylinder with blueberries. The old neurons that encoded the blue box form connections with two new blue cylinder neurons, encoding the cylindrical shape and new time period. A weak connection forms from the blue cylinder neuron with the green cylinder encoding neuron. A single neuron does not encode both the blue square and blue cylinder because the memories are too far apart in time, unlike the blended neuron that encodes the blue and orange boxes together. Finally, no connections are made between the new blue cylinder neurons and the old orange box neurons as they have no over lapping elements. This is an example of keeping memories in distinct schemas.

The dreams made in Inside Out versus real dreaming:

I think Inside Out could have done a much better job with depicting how dreams are made. In the film, dreams are made on a movie set complete with a director, writing staff, actors, and even a make up crew. Where Inside Out was most accurate was using events of the day to influence the writing of dream’s scripts. However, this is sort of where it ends. We do not know exactly what dreaming is, but we do know that during sleep episodic like memories from the day are replayed in the hippocampus (also see here). Hippocampal replay is the process in which a specific sequence of neural activity is “replayed” but at a time scale much faster than what would have been experienced in the real world. However, we know this process happens while we are awake too and may help us to plan for the future. This replay during sleep is vital for efficient learning. These replay events in the hippocampus also have down stream effects on cortical regions and likely play a role in memory consolidation. Researchers are able to apply a bit of electricity (no harm done) to a small part of the hippocampus when a replay event begins. This electrical stimulation blocks the replay, or dream, from happening. Without replay events, rodents take a very long time to learn a task and perform poorly compared to animals without stimulation. Thus, we know the replay of episodic memories during sleep is important for learning and consolidation.

Inside out could have utilized their memory sphere’s of episodic memories to replay during sleep. The movie set idea could have still worked, the writers would just be tasked with taking all the new memories of the day and replaying them in such a way that they associated with memories already stored in long term memory. Then, if the dream was well written, the memory spheres would have gotten a brighter glow and they would be sent off to be with other spheres of similar memories. This would mean totally new and unique memories to be a big challenge. If the dream of brand new memories was written poorly, the memory may degrade. If the dream was written well, the new memory would get its own book shelf in long term storage where other like memories could be sent. These details could have added a lot of accuracy to how sleep and dreams likely work.

Miscellaneous Neuroscience and Psychology of Inside Out

Core memories of personality:

I’m with Dr. Novella on this one, I’m not too sure the idea of a few core memories shaping someone’s personality is all that accurate. It is well known that genes play an important role in personality and research is beginning to uncover ways genes play into different personality traits. However, I don’t think the core memory concept in Inside Out is totally wrong. Our memories certainly play a big role in our personalities. We also know experiences can shape a person and even alter their DNA; a field called Epigenetics studies how experiences change our genes. And there is evidence that mice can pass on olfactory memories to their offspring, even after 2 generations. All in all the core memories were a nice story telling tool to convey personality. Perhaps it was the influence of her father’s love for hockey ingrained in his DNA that gave Riley a propensity to also love hockey.

A nice touch could have been new memory spheres relating to a Core Island theme being sent to the related Core Island rather than just to Long Term Storage. This could have been a nod to the memory schema theory I discuss above; like memories are stored with like memories.

Reconsolidation of Memories:

In the film, memories were replayed in full fidelity and could be replayed over and over without the memory being changed. However, some research has shown replaying memories and the resulting reconsolidation of memories can result in the memory being changed or degraded. The rewatching of memory spheres could, in some cases, cause them to be altered or fade.

Imaginary Friend:

Riley had an imaginary friend when she was younger. The emotions Joy and Sadness encounter this imaginary friend wandering around in the long term memory storage. Inside Out depicts this imaginary friend as an odd looking creature consisting of a cotton candy body, elephant trunk, cat tail, and the ability to make accurate dolphin calls. Riley’s imaginary friend, called Bing Bong, was formulated with whatever information she was receiving during her young childhood, as Bing Bong puts it, “animals were all the rage back then”. I like the idea of representing an imaginary friend as a whole character rather than as a memory sphere/s. Of course, for the sake of story telling, Bing Bong needs to be a character as he advances the plot in pivotal ways. But by making Bing Bong an entire character, similar to how the emotions are depicted as characters, shows how complex it is to form an imaginary friend. Visual stimuli have to be combined in such a way to make the character in the child’s mind. A voice needs to be made. Then it has to be attributed to a personality, no easy feat considering children are only beginning to master the theory of mind around age 2-3.

Inside Out Conclusions:

I thoroughly enjoyed Inside Out and I think the movie depicted the brain and a lot of its mechanisms in a realistic enough fashion. I hope the movie gets people thinking about the processes in the brain and brings them an awareness as to what goes into things they take for granted, like memory storage and recall. Hope you learned something here!

Here is a video version of this article:

All images from Inside Out are copyright of Disney and accessed here: http://movies.disney.com/inside-out/



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