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The Mind Is a Plaything of the Body

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"The awakened, the enlightened man says: I am body entirely, and nothing beside; and soul is only a word for something in the body. Your body is a great intelligence... your little intelligence, brother, which you call "spirit", is also an instrument of your body, a little instrument and toy of your great intelligence."note 

Maybe it's just the animal instincts associated with your new form, a change in hormones or the complete rewiring of your neural circuitry, but for some reason the process of shapeshifting tends to also transform the very way you perceive and think about the world around you.

This may be relatively minor (e.g., you notice smells more and food seems more exciting) or may be so extreme that you're not even recognizable as the same person any more. The latter is particularly tragic when a more drastic change is combined with a permanent transformation, as it can be seen as a form of death. It is also sometimes used to bless a voluntary shapeshifter with suck. The classic Wolf Man fits this trope perfectly: a normal human most of the month but a rabid wolf/wolfman under a full moon.

The title of this trope is a paraphrase of Friedrich Nietzsche's declaration that the mind and soul are completely illusory products of one's physical brain and body (page quote).

Often part and parcel of the Superpowered Evil Side and Transhuman Treachery. See Sense Freak for a much milder example, and Loss of Identity for the much more extreme end result. Cybernetics Eat Your Soul is a subtrope. Can lead to Immortal Immaturity and the Second or Third Law of Gender-Bending — in fact, this tends to be especially common in magical Gender Bender fiction.

Compare Becoming the Mask, Shapeshifter Mode Lock and And I Must Scream; contrast Different for Girls. May lead to/from Sense Loss Sadness. Often overlaps with Furry Reminder and/or My Instincts Are Showing. A common cause of Bemoaning the New Body — unless the mental change is so drastic that the changed character doesn't even know what's happening.

For the exact opposite effect, where the body is a plaything of the mind, see Your Mind Makes It Real and some forms of Empathic Shapeshifter / Self-Perception Shapeshifting.


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    Asian Animation 
  • In Pleasant Goat and Big Big Wolf: Mighty Little Defenders episode 33, goats Paddi, Tibbie, Sparky, and Jonie have just been transformed into wolves by General Wolf, and Paddi starts to chew on Uncle Gogoa's arm, Uncle Gogoa being a goat who wasn't transformed. Later, Paddi says he found Gogoa looking delicious, and Tibbie, Sparky, and Jonie admit the same.

    Comic Books 
  • Alpha Flight: Snowbird runs the risk of Shapeshifter Mode Lock if she stays in animal form too long—because her mind gets subsumed by the animal. She once had to be talked down by Wolverine while she was an actual wolverine.
  • Watchmen: Doctor Manhattan has been drifting away from humanity ever since he got his new body. Since he experiences all of his life simultaneously, he becomes distant, but having nigh-limitless power and an indestructible body certainly changed things for him as well.
  • She-Hulk: Jennifer Walters starts out as a somewhat demure lawyer — her transformation initially makes her far more aggressive and angry. Over the years, her continued use of the She-Hulk form has meant that the effect of her powered up form is simply a far more uninhibited version of herself.
  • Spider-Man:
    • In the "Six Arms Saga", Peter Parker's attempts at removing Spider-Man's powers using a serum backfires, at first he grows four additional arms, and then mutates into a gigantic spider-human hybrid called Man-Spider. He loses complete control of himself and attacks and overpowers many superheroes attempting to restrain him.
    • Dr. Curt Connors is a decent fellow, but when he mutates into the Lizard, he forgets who he was and becomes a violent reptile supremacist.
    • When Morbius stands trial for his crimes committed as a living vampire, She-Hulk gets him declared not guilty by reason of insanity, because when his body needs blood, he loses all control of himself. Later, in his third solo series, he messes up a cure and becomes more and more bat-like. He begs Spider-Man for help because he fears that soon, there will be nothing left of him except a raging beast.
  • ElfQuest: The explanation for why Timmain eventually abandoned her people, and later, why she remained white-furred even though it was dangerous: She was very deeply subsumed into the wolf-form she originally shapeshifted into for survival.
  • Hellblazer: Constantine faces off against a criminal's ghost that has possessed a man-eating junkyard dog. Constantine eventually manages to trick him by lying down and rolling over onto his back. The criminal is left unable to attack any further, as presenting one's belly is a sign of submission in canines.
  • An arc of JLA (1997) deals with General Ripper Wade Eiling swapping his mind with that of the Shaggy Man, a nearly indestructible monster. He reasons that his tactical experience combined with the Shaggy Man's brute strength will make him an unbeatable Genius Bruiser, but he is defeated when it turns out that his new brain isn't half as sophisticated as his old one. Though he retains his skills, knowledge, and intellect, Eiling's actual thoughts and awareness are a lot simpler and sloppier, and as a result he tends to forget details or fall for traps that he never would have as a human.
  • Johann Kraus from Hellboy used to be a German spiritualist who could project his spirit into an ethereal form until his body was destroyed while he was outside it. He was left permanently trapped in ghost form, forcing him to use a repurposed hazmat suit as a makeshift body, and as the series progresses, his personality gradually changes as he drifts away from a human perspective, becoming more aloof, distant, apathetic, and self-centered. It cuts the other way too, as when he temporarily gets a new body later on, the shock of being able to experience basic human pleasures again after decades of being stuck in a gaseous state causes him to become an extreme hedonist obsessed with eating, drinking, exercising, having sex, and whatever other physical activities he can think of.
  • Zigzagged in Daredevil in a somewhat convoluted manner. A brilliant but physically weak scientist named Dr. Karl Stragg transfers his mind into the body of the strong but dumb Enforcer named Ox. Stragg's intelligence gradually starts dropping, which leads to his death fighting Daredevil, while Ox finds himself getting smarter in Stragg's body. Later on, radiation experiments mutate Stragg's body, transforming it into an identical (but grey-skinned) copy of Ox's original body to match its current mind, but Stragg's mind also somehow resurfaces after he is fully transformed.
  • The Incredible Hulk: On occasion, the situation with the Hulk is that Bruce transforms into the Hulk's body, but retains his own mind (rather than switching personalities). Often, however, Bruce still finds it very difficult to think or keep calm while in typical Hulk form.
  • Zenith: In Phase IV, Dr Michael Peyne is given the dubious gift of reversed aging by the Lloigor, and his mind is not spared the effects, as is demonstrated by his Apocalyptic Log: once Peyne re-enters his teenage years, he feels restless and moody most of the time; as a child, he grows increasingly bored with writing his memoirs to the point that he decides to go and play instead... and as a toddler, Peyne's writing style deteriorates into halting monosyllables in a clumsy scrawl, the spelling getting progressively worse and worse until he finally gives up and has a nap. When Ruby arrives to say goodbye, Peyne's a baby, and a bit of mind-reading confirms that his mind is now too simple to make sense of his own memories.

    Films — Animated 
  • In Batman vs. The Teenage Mutant Ninja Turtles, Donatello assures Batgirl that this is not the case with Ooze induced animal transformations. You may have some new animal instincts, but you're still fundamentally yourself. It gets played straight when the Ooze is combined with Joker Venom to create a true Psycho Serum.
  • Brave: This was a problem for Queen Elinor and the prince in the legend when they are turned into bears.
  • Beauty and the Beast: According to the director's commentary, the spell affected the Beast's mind as well as his body; the longer the spell lasts, the more feral he becomes. When Belle arrives, he has to re-learn how to read and eat with utensils, and if she had never come to the castle, he would've eventually stopped speaking, stopped wearing clothing altogether, and would've gone to live in the woods, becoming a beast both inside and out.
  • Played for Laughs in Soul, Joe takes on some catlike mannerisms while in Mr. Mittens’ body, i.e. sleeping in a sunbeam.
  • In The Super Mario Bros. Movie, Mario is compelled to act a bit cat-like while using the Super Bell, which gives him the Cat Suit. More exaggerated in the Japanese dub, where he ends almost all of his sentences with a compulsive "nyah."
  • In Turning Red, Mei gains the ability to transform into a huge red panda. Whenever she's transformed, she throws her arms in the air when she's scared. This is actually a threat display used by red pandas wherein they make themselves look larger in order to scare off predators.

    Films — Live Action 
  • In An American Werewolf in London, David Kessler transforms violently into a werewolf, screaming for help as he becomes less and less human. As a werewolf, his only instinct is to kill and to feed, violently ripping his random victims apart. As he is doomed to continue this so long as he lives, his deceased friend Jack begs him to kill himself. The second time he changes, David is briefly calmed when the young woman he fell in love with attempts to save him from being shot; Sadly, he is too far gone and thus killed right in front of her.
  • In the My Favorite Martian movie, the alien polymorph gum can alter one's personality, depending on the alien. This comes up later, where the hero's nice and mild-mannered girlfriend chews one, turns into a giant alien monster, and kills a couple MIB guards, even eating one. Afterward, she acts as if she had just been in a drunken party.
  • Subverted in the Day of the Dead (2008) remake. Bub is a vegetarian and thus doesn't want brains, and he follows orders due to being a marine and/or having a crush on Cross.
  • Subverted in Land of the Dead. The gas station attendant zombie initially remembers that he's supposed to do something with the gas pumps. As the movie progresses, he regains more and more of his humanity, including compassion for his fellow zombies, tool and gun use, and even leadership.
  • In The Fly (1986), the scientific genius Seth Brundle fuses with a fly, and as his body slowly begins to morph horribly, he realizes that, to his terror, his personality is being overridden by the instincts of the mindless insect. Arguably, the last we see of his original personality is when the crippled wreck that Brundle has become mutely begs for death.
  • Captain America: The First Avenger: To some degree, this is inverted with Schmidt who developed his... unusual features in response to the serum because the serum hadn't been perfected yet and he was an evil man at heart. As its creator said, good becomes better, bad becomes worse.

    Live-Action TV 
  • In The 10th Kingdom, Prince Wendell swaps bodies with a dog and gradually starts thinking like a dog, the dog also slowly starts thinking more like a human (but never quite gets it) although this may simply be training.
  • Andromeda: The physical avatar that Harper builds for Andromeda is initially just a more solid presence for the ship's AI than the holograms she normally uses, but over time, dealing with humans and aliens on a more intimate and physical level, Rommy develops a more emotional and independent personality. Even the holograms have a slightly different personality than the 2d avatars she uses on consoles; occasionally the three get together for consultations.
  • BrainDead (2016): Possibly. It is unclear whether the alien bugs' becoming embroiled in our political squabbles is all part of their plan for conquest or is in fact a derailment of those plans, perhaps because they have no conception of ideology and take their absorbed opinions for Absolute Truth.
  • Buffy the Vampire Slayer:
    • When Giles is turned into a Fyarl demon in "A New Man", his instincts tell him to smash things, like Fyarl demons are wont to do. The more time passes, the harder it becomes to keep those impulses under control.
    • Oz's werewolf attraction to Veruca is clearly hard to keep in check, but he manages. That is, until sunset on a full moon night — he loses it after the first stages of transformation.
  • Doctor Who:
    • The result of regeneration. While certain deep traits and values are maintained between every incarnation of a Time Lord, other parts of the personality can become massively different, in addition to being completely loopy and extreme for a day or so as they settle into each new personality. As the Fourth Doctor comments in his initial episode, "A new body is like a new house — it takes some time to settle in." Every Doctor (with the exception of the Ninth, whose initial regeneration wasn't seen) gets an initial storyline about figuring out what their own personality is like, and every Doctor seems to have their own view on how much of a change this even is: One viewed it as a straightforward continuation ("it's not over!") but his successors as "replacements"; Three's was tangled up with Buddhist symbolism concerning change and renewal; Four viewed it as a death, although one he was happy to accept by the time it happened; Seven thought it was a change of perspective; Eight described each incarnation as a different and separate life; Ten described it as an actual death where "some new man goes sauntering away"; and Eleven's comments suggest that they're like the phases everyone goes through.
    • In "Daleks in Manhattan"/"Evolution of the Daleks", Dalek Sec merges himself into a Dalek/Human hybrid for the sake of experimentation and prolonging the Dalek species. As a result, he becomes kind, rational, and outright resents what he used to be. The other Daleks don't take that very well.
  • Dollhouse: In "Instinct", Echo is programmed to believe she is a mother with a baby, not only with her memories but also her glands to induce lactation and parental bonding. Thus, even after Echo's memories are wiped, she still instinctively seeks out the baby to protect him.
  • It's implied in The Flash (2014), and confirmed in a deleted scene, that Eobard Thawne Took a Level in Kindness to some extent and became more mellow in his Harrison Wells disguise because he used DNA harvested from the real Wells. Future incarnations of Thawne still have the Wells disguise, but are more openly evil and violent.
  • A crossover episode of Kamen Rider Gaim features the story of Ryoma Sengoku, who placed his brain into the robotic body of Hakaider, which ended up making him behave more and more Ax-Crazy — something that he found out much to his horror when he returned back to his human body.
  • Quantum Leap saw a little bit of this at times, usually attributed to the "Swiss-Cheese Memory" side effect of Leaping. In one episode Sam leapt into a retarded man and exhibited some of those same traits in living his day-to-day life.
  • Space Cases: In the Personality Swap episode, turning human doesn't grant Radu any new powers like the others, except that he automatically assumes the role of the leader and starts ordering the others, who follow him, just not entirely happily. Apparently, a superiority complex comes with human DNA, though it should come as no surprise since Harlan explained this while he was still human. Rosie's and Bova's personalities are also characteristic of their species and swap accordingly.
  • In the Star Trek: The Original Series episode "By Any Other Name", the Kelvans (huge emotionless hundred-armed aliens from the Andromeda galaxy) take human form. They eventually start thinking like humans, including having human emotions.
  • Star Trek: Voyager:
    • Members of Species 8472 suddenly become much more willing to negotiate after taking-on Human disguises in the episode "In the Flesh".
    • In a reverse example, Ensign Lindsay Ballard is unable to reintegrate back into her life on Voyager after having been transformed into an alien in "Ashes to Ashes".

    Newspaper Comics 

  • Religions that believe in incarnated gods have a variety of beliefs in the degree of influence those bodies have on the god during the incarnation, though usually (universally?) the essential nature of the god remains the same throughout. Christian theologians and sects disagree on the nature of Jesus' humanity, some (for example) holding that Satan could never actually tempt him with food or power, while others holding that he must have or else the 'temptations' were meaningless. Hindu stories strongly imply that incarnated gods will usually forget their divine natures entirely while on Earth unless enlightened to them.
  • In those belief systems that hold with souls' preëxisting birth, some hold that the soul's essential nature and fate are eternally mutable, others that behavior whilst embodied determines the soul's condition for eternity.

    Tabletop Games 
  • Dungeons & Dragons: Played straight with the spell Polymorph Other in the first and second editions of AD&D — aside from a chance of simply killing the target, its original personality could be subsumed by one more appropriate for the new form either instantly or over time. This is used as a plot point in the Dark Elf novel Exile, written in the second edition era, which features a sympathetic supporting character turned into monstrous form by an evil wizard and fighting a losing battle against the instincts that come with it. He dies in the end before his comrades can find another wizard to undo the spell.
  • Genius: The Transgression: Subverted. Shapeshifting yourself or others explicitly doesn't affect your mind. The example given is trying to turn a rampaging, bloodthirsty T. rex into a docile rabbit; what you get from that is a bloodthirsty rabbit. However, turning someone into something that isn't alive will cause them to lose consciousness until they're reverted. If you really want this to apply, you need to use a powerful mind control device alongside your transforming device.
  • In GURPS: Magic shapeshifting slowly drains the IQ stat. If it drops to five (animal level) the transformation becomes permanent.
  • In Mage: The Ascension mages can shapeshift using the sphere of Life. However, if you do not have Mind magic, or the highest rank of Life magic, you eventually take on the mind of whatever form you have shifted into. You can also leave out the Mind magic and force others to change shape causing your enemy's intellect and self image to slowly melt away over the course of weeks to be replaced by an animal's.
  • In FreeMarket, this is given as the justification for why you have to play some sort of human — albeit potentially a significantly modified one — rather than a catgirl, a total conversion cyborg, or a robot with a human mind uploaded — putting a human mind in an inhuman body causes the mind to become inhuman — or, in more plain terms, the person goes insane.
  • Warhammer 40,000:
    • The pilot of a Titan, called a Princeps, must psychically dominate the much greater and more powerful mind and spirit of the Titan. Even if this works, which is by no means guaranteed, the Princeps becomes addicted to being attached to their Titan, as they become accustomed to being the much larger and more powerful being and find it very hard to return to a human mindframe. The powerful mind of the Titan will eventually consume the Princeps', whereupon the minds fuse and the Princeps would die if detached. To plan for this, the Princeps is sometimes hard-wired to the Titan to start with. This will happen automatically if the Titan falls to Chaos, and the Princeps is then merged physically as well as mentally.
    • This idea is explored again with the Hellbrute, which was originally a mech-like machine called a Dreadnought that allows for a near-dead Space Marine to keep fighting, but has been possessed by a Daemon and has a Chaos Space Marine in it instead. The machine starts to gain its own intelligence as the Daemon takes over it, and the Chaos Marine's mind begins to fuse with the Daemon, eventually turning the Daemon, Marine and machine into a single more or less mentally cohesive amalgam. This is actually a mercy for the Chaos Marine, as the previous concept of the Chaos Dreadnought did not have the Daemon in it, and the Chaos Marine, stuck inside a robotic shell with no sensory input, inevitably went mad.
  • The player characters of Changeling: The Lost escaped Fae torturers mostly intact. They're still humanoid mortals who have free will, but Fae magic has marked their body and soul. Beast changelings still have human intelligence, but they will always be slower in using it. A Flowering may distinctly remember and fear being pruned, even though their body isn't a true plant anymore.

    Video Games 
  • Paper Mario: The Origami King: The Toads who were folded into animal shapes gained a full set of animal instincts while in those forms — including against their wishes in some occasions, as noted by a Toad-turned-cicada who notes that he was being driven crazy by the noise he felt compelled to constantly make and by a number of others who note they wouldn't have fled from Mario's attempts to rescue them but did so because their animals forms were skittish by nature. Notably, several retain animal mannerisms after being unfolded, such as former Toad-turned-dog who barks and growls in his speech and several former Toads-turned-butterflies who keep running around while flapping their hands.
  • Pokémon:
    • In the universe of Pokémon Mystery Dungeon, it's implied that this can happen when Pokémon evolve. In particular, a Lombre is unsure whether or not he wants to evolve into a Ludicolo, because Ludicolo are carefree Pokémon and he isn't sure if he wants to be carefree.
    • Also in the same game, there are multiple implications that not only did the Player Character's body became that of a Pokémon's, their "thoughts and feelings" became more like one's as well. It comes to a point when they are introduced to their rescue team base, and the player is suddenly very happy with it. They even contemplate whether their feelings are truly their own thoughts or simply a "side-effect" from becoming a Pokémon.
      Hero: Wow! I can't explain, but I'm happy! I'm a human being, but I like this place. I feel weirdly happy! It might be an instinct thing for Pokémon... Maybe this is what it feels like to want to wag your tail... It doesn't matter! I'm happy! Maybe I feel that way because I'm <Pokémon>!
    • This carried over into the anime as well.
      • Notably, Ash's reliable and obedient Charmander evolved into grumpy and unresponsive Charmeleon, who further evolved into an even more disobedient and aggressive Charizard. This is supposed to reflect how, in the video games, a trainer can't fully control a traded Pokemon whose level is higher than the badge allows. For example, you can have a level 50 Charizard, but unless you get all the badges, it won't always listen to you. Charmander was, technically, a traded Pokemon. Although Charizard never followed his orders until Ash stayed up rubbing his hands raw to defrost Charizard after it was encased in ice.
      • Dawn's Swinub/Piloswine/Mamoswine act exactly like Ash's Charmander/Charmeleon/Charizard, except it retains its obsession with Poffins.
  • A possession example: In the video game Geist, you can inhabit the body of various mice. While you retain control during those sections, your body is inherently attracted to the cheese in the nearby mousetraps, often to the point of affecting or overriding your control. Also, the body's own preferences can prevent the player from going places. When the player possesses a woman in the shower, she refuses to exit into the hallway (guarded by a male soldier) until she puts on her clothes. And after the player attacks an engineer with a pair of robotic arms to scare him, he'll never go near them again.
  • In Metroid Prime 3: Corruption, the cyborg hunter Ghor is quiet and unassuming — until he plugs into his large mecha/Powered Armor hybrid, instantly becoming gruff and hyperaggressive.
  • The reason given in Eternal Darkness for why Chattur'gha trumps Xel'lotath. (Necessary, since using the mind-over-matter philosophy would break the Elemental Rock-Paper-Scissors.)
  • In Sanitarium, the main character involuntarily changes forms throughout the game. Each form has a distinct personality, their own unique (fake) memories, and their own voice actor. Near the end of the game, he gains control over these transformations. During his first few voluntary shifts, he frantically reminds himself who he really if afraid one of the other personalities will take over.
  • In Dragon Age: Origins, the aptly named Mouse is a Mage Apprentice who shapeshifted into a mouse and can't change back in the Mage Origin. He actually talks about how his shape is well suited to hiding and sneaking and that's most of what he does nowadays as the reason why he can't change back. Subverted, as this happens in the Fade (i.e. the dream world) and he's not actually a human, but a disguised Pride demon trying to trick you.
  • Kemono Friends:
    • Animals from all around the world gathered in a giant park are turned into human-like girls due to a mysterious substance known as Sand Star. They all acquire human-like intelligence and although keep some characteristics tied to their original species, generally are mostly human-like in behavior, some of them even getting into hobbies like reading, watching TV and playing video games.
    • In the Sgt. Frog collaboration event, the 5 aliens invaders from Sgt. Frog are turned into human-like girls too due to the Sand Star. Their personality quickly adjusts to match their new bodies. All of them soon identify as girls, although Giroro initially attempts to deny it, wear female clothing without issue, and in Giroro's and Dororo's cases there's even a complete change of their speech style. Although they initially set out to go back to normal, by the end they indefinitely delay that in order to help the game's protagonists in their quest.
  • King's Quest:
    • Played with in The Kings Quest Companion chapter for King's Quest III. The cat cookie spell eventually robs the sapience from the person afflicted with it, trapping them in a feline's body forever. Yes, it is a Fate Worse than Death, but considering Manannan inflicted it on his enemies several times and was going to kill Alexander as soon as his usefulness was up, this makes it closer to Hoist by His Own Petard. In King's Quest V, which takes place several years later, Manannan is still sapient and capable of human speech, but then again he dies by being trapped in a burlap sack, because he wanted to eat a dead fish.
    • In the third chapter of King's Quest VII, there is a lord who has been turned into a stag, and he says that the longer he is forced to stay in that form, the harder it becomes for him to use rational thought, and implores the protagonist to help remove the curse on the forest before he forgets himself completely.
  • Commonly theorized to be involved in Final Fantasy VII with Sephiroth. After he manages to turn the tables and take control of the Eldritch Abomination that was trying to Grand Theft Me him, he develops a sudden interest in devouring the Lifestream. The theory is, that's just how Jenova's hunger instincts work.
  • In Kingdom Hearts: Birth by Sleep, Xehanort's entire fighting style changes when he body-jacks Terra, exclusively using all his victim's best moves — with the eventual addition of the Dark Figure.
  • In Portal 2, GLaDOS's body has some built-in functions that affect any artificial intelligence connected to it. The helpful but stupid Wheatley is corrupted by the body to become evil and obsessed with testing and he is quickly overwhelmed by how much power he has. Though later, this is also revealed as a function of the body — to ensure that cores would be convinced to keep testing. He's still rock-stupid though.
  • In the first Ratchet And Clank game it doesn't matter what enemies are doing prior to being hit with the Morph-O-Ray; after it's turned them into chickens they just go about their chickeny lives.
  • In Kid Icarus: Uprising, when Pit is temporarily in control of a dog's body, he's drawn to the food garbage in the street. This results in him automatically walking away from where you need to go, and the player has to fight with the controls. When you're in control of a human, however, Pit doesn't take on any aspects of their personality.
  • Resident Evil: The Darkside Chronicles: Played with when Manuela's mother mutates into a giant, feral fish/lizard monster and it turns out that her love for her daughter is the only spark of humanity left within her.
  • Two characters in Digimon Story: Cyber Sleuth are comatose humans possessed by Digimon with their personalities being amalgamations of the two individuals. For example, Kyoko's penchant for weird coffee additives like oyster sauce and mayonnaise comes from Alphamon not knowing what's normally added to coffee.
  • Purah from The Legend of Zelda: Breath of the Wild plays with it and subverts this. Originally a 100+-year-old, she uses an experimental rejuvenation process on herself that leaves her physically a six-year-old, with the requisite childish personality. However, comments from other townspeople as well as her own appearance in the prequel reveals that she always had that personality to begin with, even as an adult. On the other hand, reading her diary reveals that, as she was passing down through her teenage years, she briefly exhibited a rebellious and resentful personality and a penchant for "teen" slang.
  • Although it only sort-of involves shapeshifting, this trope is present in Starsiege. When humans undergo the "Methuselah Process", their squishy brain is replaced with a cybernetic one, preserving their personality and memories. That cybernetic brain can later be transferred to a new body. However, transferring bodies often results in "Cell-Memory Drift", where the personality stored in the cybernetic brain is influenced by the personality of the new body's former owner. This is why when the cybernetic brain of Victor Petresun was implanted in the body of young Harabec Weathers, Victor so strongly embraced the identity of Harabec. It's also why Emperor Solomon Petresun never changed bodies, preferring to keep his original body on life support long past its normal expiration date.
  • In AI: The Somnium Files, this is part of Saito Sejima's motivation for his crimes: he was born with a brain defect that made him unable to feel positive emotions normally, but gave him an immense rush of pleasure every time he took a life. At one point, he used a Psync machine to perform a Body Surf, but this left him stranded in a body that has a "normal" brain, letting him experience the full spectrum of emotions but also depriving him of the joy of killing. Since he'd become addicted to murder at this point, he absolutely hated this, so one of his goals is to swap back into his original body so he can fully appreciate killing people once again. As for the current owner of Saito's brain, Kaname Date is kept in line by regular doses of synthetic oxytocin which compensate for its deficiency and allow him to be a functional human being.
  • Galaxy Angel II: Nano-Nano Pudding is a living nanomachine colony that usually takes the form of a young girl, but she is able to alter her human appearance and transform into other people if she wants to. She does not like using this ability to impersonate people she knows, as the more she stays transformed, the more her memories and personality are at risk from being overwritten by those of the person she is replicating (this becomes a problem in her route in Mugen Kairo no Kagi, when her memories start being replaced). She's completely fine with shapeshifting into someone she doesn't know as there is no threat of memory loss.

    Visual Novels 
  • Somewhat present in Ever17. While possessing Hokuto, Blick Winkel essentially thinks he is Hokuto. Blick Winkel's discovery of his own existence becomes a major plot point.

  • Gunnerkrigg Court:
    • Reynardine mentions the trope when Kat observes that his personality is more pleasant when he's in his wolf form than when he's a pint-sized plushy. It turns out to be an Inverted Trope: he changes form based on how he's feeling.
    • Alistair is permanently turned into a bird, with "a bird's brain and all that entails." Word of God clarifies that the personality remains the same, but behaviour is affected by the body — though the presence of sapient pigeons in the setting muddies the waters.
    • Coyote once tells a story of the time he spent an extended period of time as a dead goose in a bush by a lake (that's all three things at once, by the way) because he forgot who he really was in that form.
    • Loup in the guise of Jerrek has an internal monologue that suggests that the assumed personality is becoming less fake as time goes on.
  • In El Goonish Shive, transformations tend to influence the transformee's behavior somewhat, usually in subtle things like body language (for example, someone turned into a cat-person might find themselves purring without realizing it), and the author has said he enjoys adding goofy little quirks like that: for example he finds it especially funny when Elliot gets genderbent and then acts in a girly way without realizing it.
  • Ash in Misfile has gone under some relatively minor behavioral changes after being turned into a girl, however, unless s/he's having a period, it's nearly impossible to tell which of the differences are biological and which are due to circumstances. At one time Emily wondered whether differences in male and female brains might be responsible for Ash's poor math skills (it wasn't, as Ash sucked at math both before and after the change). That said, Ash's personality hasn't changed that much, so this is largely subverted.
  • The Dragon Doctors: Four of the five main characters suffer a bit of this as a result of getting gender-swapped.
  • Cole in CharCole tends to surrender to his Charmander instincts whenever he's in mortal danger, and sometimes needs to be snapped out of it by force.
  • Ozy and Millie presents Pirate Captain Locke, who comes from a world where people are born adults and age backwards. Locke became accordingly less mature as he de-aged.
  • Bec Noir in Homestuck is beholden to Becquerel's canine desires. He also seems to have acquired Bec's Undying Loyalty to Jade.
  • Eerie Cuties:
    • After a "Freaky Friday" Flip chocolate craving cute-vampire Nina, and standard vampire Layla find their normal cravings and personalities switching to suit their new bodies.
    • Subverted with Ace after a Gender Bender transformation. She just likes to pretend it is this trope, much to the disgust of those around her. However, the Gender Bender curse seems to affect the victim's mind based on how masculine they were before the curse. Ace found himself attracted in men and interested in dresses. When the curse transfers to Kade, he becomes a very willing magnet to many a guy.
  • In Prezleek Comics, shapeshifting elf Helwyr turns into his wolf-monster form, only for Prez to subdue him with belly rubs like a dog. Then he turns back.
  • Kill Six Billion Demons: God-Emperor "Mottom" Nadia Om is able to change her apparent age through use of a de-aging fruit with temporary effects, with three particular ages being used throughout the story. As the Maiden, she's sanguine, arrogant and demanding, as the Mother she's melancholic, reflective and analytical, while as the... Other one... She's phlegmatic, acerbic and bluntly-spoken. Despite having lost her fruit by Breaker of Infinities Mottom is energized by the Final Battle into de-aging herself through pure willpower, allowing her to stay in Mother form for her Final Words.

    Web Original 
  • In Buster Girls, being transformed into a Heartless or one of their minions usually includes a full personality shift to fit their new form more (assuming there's even a personality left).
  • The various characters who transform in The Cartoon Man not only undergo physical changes, but begin acting like cartoon characters as well.
  • Critical Role:
    • Use of the Polymorph spell is limited by the fact that, unlike with Wild Shape, anyone who is Polymorphed also inherits the mental statistics of the creature they transform into. Perhaps the most famous example is when Jester is sent to spy on a secret meeting while Polymorped into a moth... but because moths have an Intelligence score of 1, she has to roll an Intelligence check to see if she even remembers what she was supposed to be doing. When she finds that she can't actually get into the room because the curtains are drawn, she spends the rest of the spell's duration chewing on said curtain, followed by her falling out of the window once she turns back into her normal self.
    • Later in the second campaign, Caleb, Jester and Reani are sent to spy on a house while transformed into bats, but while Reani's Wild Shape allows her to retain her mental status, Caleb and Jester are stuck with an Intelligence of 2. Caleb, who is otherwise the most intelligent member of the group, is hit especially hard by this, as his first course of action is to check the roof for bread.
  • In Link and Mage, being physically transformed into a Familiar by a Witch comes with the fitting mental change. In regard to the main characters, their outfits show the amount of control a Witch has over them. Once their outfit has fully turned into that of a Familiar, they're also fully under the control of the Witch.
  • New Life SMP: Every time Sparrow shifts between origins, his personality seems to change to fit the origin as well — as a Copper Golem, he prizes efficiency and shuns human attachment; as a Sculk, he's keen on spreading the darkness to the point of murdering anyone who dares to "disrespect" or oppose it. Scott speculates that these changes may be related to Sparrow artificially changing origin rather than dying of natural causes like anyone else on the server, since no one else has experienced these personality changes on a such drastic level, which is suggested to be true to some extent in Owen's finale as Sparrow.
  • Rats SMP: After their Forced Transformations into cats on Day 39, El and Will start showing a distinctively more feline traits, including a taste for milk and occasional meowing. In Will's case, it's Played for Horror as their forcibly feline appetite preference extends to them having to visibly resist eating their own close rat friends… and they offhandedly mention on Day 57 that they still have occasional intrusive thoughts about the latter despite being returned to their original form and being vegetarian.
  • In the Whateley Universe, most of the main characters underwent Gender benders when their powers manifested; apparently turning a happy boy into a girl doesn't cause gender identity disorder and since the Unfortunate Implications are glossed over (they get therapy, but it's off screen) to the point you'd rarely realize they hadn't been a girl all their life.
    • Varies from person to person, some change form without any mental effects, some had GID before the change, and its mentioned in passing that some people have developed GID after flipping genders.
    • Main protagonists Team Kimba right now have 7 characters: two had GID before they became mutants; two have spirits (or something more powerful) riding along helping them acclimatize; one seems to just magically be happy going from girl to boy; and two are massively pissed and unhappy about being shifted.
    • It's also been known to affect voluntary shape-shifters, to the point they have classes on maintaining an identity.
    • It's actually specifically mentioned in a few of the original stories (such as Fey 1) that being an Exemplar (Mutant with Most Common Superpower as an actual power) specifically invokes this trope. That is to say that as a rule, if you are shape-changing due to being an Exemplar, eventually you'll get used to your new body — no matter if it's female, a mutant T. rex, or a giant piece of sentient coral. The fact that BITs are generally based on the Exemplar's subconscious idea of a perfect body also helps.
    • Present in another capacity with regards to the J-Team, though it's possible that it's just Jade's flair for the dramatic showing through. Whenever she creates another instance of her consciousness to possess something, it acts more or less how you would expect a sentient version of that thing to act. The best example here is probably Shroud/Jinn, who acts a lot more mature than Jade, and pulls off a pretty convincing 17-year-old.
  • You Have Become Your Avatar: Some users fall victim to their Avatars' canon personalities and attempt to act them out. Ichigo Pocky Chama got trapped in the body of Deidara and immediately got the desire to blow things up for the hell of it.

    Western Animation 
  • Batman: The Brave and the Bold: De-aging to a toddler doesn't reduce Batman's intelligence, but it does alter his behaviour — forcing him to communicate mainly in baby-talk and draw using crayons. At the end, he's able to figure out a cure for his deaging, but has to tell the Marvel family with incoherent baby noises and pointing at things.
  • In Beast Wars, a Maximal or Predacon that acquires an organic alt mode also acquires the instincts of the organism they scanned; normally, these instincts are separated from the rest of their memory by mental firewalls, but various disruptions to those firewalls (from damage to the protoform before scanning or staying in alt mode for too long) can cause the instincts to overpower the Transformer's personality to varying degrees, though a 'bot can delete the firewalls purposely and integrate the two together without any lingering effects. Arguably, a Transformer "possessed" by their beast mode is much more dangerous, as they're forced to obey their unpredictable animal instincts instead of following typical Maximal or Predacon stereotypes (for instance, the Predacon Inferno — who had his personality almost entirely enveloped by his fire ant alt mode — became fanatically loyal to his "queen" Megatron and suicidally and recklessly effective as cannon fodder, all in line with his role as an soldier ant). Tigatron, however, manages to solve this problem on his own, simply by removing the firewalls and allowing his two halves to mesh. He later passes on the trick to the other Maximals after they're forced to remain in Beast Mode after losing their shielding system.
  • Ben 10
    • In the original series, the primary purpose of Ben's Greymatter form is to make him intelligent. Ben also says Ghostfreak made him feel weird, for a good reason. Super-Intelligence is also one of the main purposes of Alien Force's Brainstorm, though the form also makes Ben act like an Insufferable Genius.
    • In the episode "Don't Drink the Water", Max and Ben are both doused with water from the Fountain of Youth, and are temporarily regressed to ten and four years old, respectively. While both retain their memories of being older, their behavior and maturity are clearly affected by their new physical ages; Max tries to avoid work and just have fun, while Ben is more easily emotionally-overwhelmed, whining about walking too long and throwing a temper tantrum when Gwen keeps talking down to him.
    • In Ben 10: Alien Force, Ben's Spidermonkey form makes him more hyper and prone to making monkey-like hoots. Turning into Rath makes him quick to anger. In one episode, Big Chill turns out to be an asexual reproducer, and gives birth to alien babies after it took over Ben's mind several times in order to build a nest.
    • In Omniverse when Ben transforms into his Inkursian form Bullfrag, he suddenly finds Princess Attea, another Inkursian, very attractive.
    • In the reboot, Kevin has this problem too. As Bashmouth he often acts like a dog (i.e. chasing after sticks or being distracted by food).
  • Codename: Kids Next Door: When a boy is girlyfied completely, the mind will change too.
  • Subverted and played in a single episode of Extreme Ghostbusters. The Monster of the Week's payload is to occupy human bodies by driving the original mind out. In the case of our Paraplegic Badass Garrett, after his body was occupied by the ghost and his mind driven out, his mind was still drawn in a (wheelchair-)sitting position, while the gang found something was amiss when the corporeal Garrett began walking...
  • Futurama: In "Teenage Mutant Leela's Hurdles", when the crew's de-aged into teenagers and then young children and babies, their behaviour changes accordingly. Farnsworth is at first unchanged because is just de-aged into his fifties, but when a botched attempt to cure himself results in him getting progressively younger, he becomes first an afroed Seventies stereotype, a hippy, a teenaged nerd and finally a Child Prodigy.
    • In one episode, Bender has his chassis converted to a Fembot. His personality (i.e. a misogynistic jerk) is initially unaffected, but the longer he stays as "Coilette" he begins to act more feminine under the influence of the robot equivalent of female hormones.
  • Kaeloo: Inverted in Episode 91. When Stumpy invokes the Personality Swap trope so he can finally be just like Mr. Cat, he gains a pair of cat-like fangs like the ones Mr. Cat has along with his personality.
  • In Rick and Morty, one of Rick's backup plans to keep himself alive was a Body Backup Drive scheme called "Operation Phoenix" that would allow him to upload his mind into younger clones of himself. He discovers the downside to this when he uploads himself into an adolescent clone so he can hang out with his grandkids. The younger body's adolescent drives overwhelm his mind, trapping him inside "Tiny Rick". He is only able to express his plight through creative expression - for example, when "Tiny Rick" does a song and dance routine, the lyrics are actually Rick begging to be let out of the body. Rick is only able to briefly return to his old self when hearing sad Elliott Smith music reminds him that he's actually an old man. The first thing he does when he returns to his original body is to hack apart the clones with an ax.
  • Samurai Jack: The titular samurai is imprisoned and forced to fight in rings for entertainment twice. The first time he tries repeatedly to refuse, angrily lecturing the audience about the plot of the episode. The second time, he's in a pit with much less to prevent escape, but he's been turned into a rooster and the POV shots showing his thoughts after the transformation have tapered off. After a single attempt to escape is thwarted he just takes the role of a loyal gamecock, fighting his opponents with claws and beak, and utterly resigned when out of the pit.
  • Sofia the First: In "Mom's the Word", Marla transforms Baileywick into a frog, and he tries fighting his instincts to catch flies with his tongue.
  • In Teenage Mutant Ninja Turtles (2003) during the three part episode "Notes from the Underground", Foot Clan-mutated laborers grew more monstrous over time and lost their identities to madness. In one example, an apparently male character whose only name was a designation, Quarry, was originally a teenaged female named Sydney.
  • A minor version in Ultimate Spider-Man (2012), for laughs: after Mesmero causes Spiderman and Wolverine to switch bodies, Spiderman (in Wolverine) uses the "I'm the best there is at what I do" line (followed by "...and I have no idea why I said that"), whereas Wolverine (in Spiderman) realises that he talks as much about inane things as Spidey does, even when there's no one to hear him.
    Wolverine (in Spiderman): Now I'm talking about how much I'm talking!
  • Taking on the form of an animal on Wild Kratts sometimes leaves Chris and Martin overwhelmed by that animal's instincts or perspective, as when the brothers became obsessed with finding shells while using hermit crab discs.

    Real Life 
  • The changes in behavior and personality caused by anti-depressants and other psychiatric medications, lobotomies, and brain injuries attest to how changes in the brain can cause sometimes major changes in the mind. All sorts of odd quirks and personality changes caused by brain disorders that go away if those disorders are ameliorated, a nice person becoming a cranky one under the influence of stress (or other) hormones, a cheerful Genki Girl who endured tons of Break the Cutie becoming paranoid and bedridden when they get old enough for clinical depression to kick in. It's very well demonstrated that the personality is a creation of the physical structure of the brain, and even minor physical and chemical changes can turn someone into a very different person, forget turning into a different species. There's also puberty, PMS, or menopause, all of which tend to induce mood swings ranging from inconvenient to debilitating.
    • Neurological studies of patients with mental disorders show that all these conditions are associated with abnormalities in brain structure and function. The way psychiatric medicines work is by causing changes in brain function that mitigate the processes that generate the symptoms forming a certain mental disorder. It's still unknown how many of these medications precisely work, since it is very difficult to link what these medications do at the biochemical level with the mental changes they effect considering the tremendous complexity of the human brain, from the complex chemical reactions that occur in each neuron to the way the millions of neurons interact.
    • There's endless medical conditions that could cause altered mental status or psychiatric disorders, but here's a small sample of those caused by physiological disorders: there are mental disturbances secondary to hyper-or-hypothyroidism. Errors in sex hormone metabolism can change the development of the body and brain, as can production of stress hormones. Speaking of sex hormones, testosterone causes what can only be called "stereotypical maleness." Cancers can produce hormones that cause electrolyte or other imbalances that mess with the mind. Tissue changes in Diabetes I and II can cause altered mental status via hypo-or-hyper blood glucose. A stroke, injury, embolism, hemorrhage in the brain can cause all manner of terrifying neural deficits depending on the part of the brain affected. A mass effect from an tumor in the head can press on brain structures. Failures of the kidneys or livers can cause all sorts of toxic product build-up or electrolyte imbalances.
    • There's also the story of Phineas Gage, a famous person one will no doubt learn about in any Psychology 101 class, who took an iron rod to the head (warning: pic might be Nightmare Fuel). He had a significant personality change as a result, and his friends remarked that he was "no longer Gage." This case began the idea that changes to the brain's physiology will have an impact on behavior and personality. Though how much of the changed behaviour was attributable to brain injury and how much to post-traumatic stress disorder, the chronic pain he suffered afterwards and the heavy drinking Gage resorted to as a coping mechanism for both are a matter for conjecture.
    • Recreational drugs change the way your brain functions, and in doing so alter yours perceptions and behavior, which are essentially transient personality changes. For example, alcohol diminishes inhibitions and makes you do things that you would never do while sober, dopaminergic stimulants can make you manic and obsess over the most mundane things, or in high doses cause paranoia, and MDMA can make you empathic and sociable. These effects generally only last while the drug is in your system. However, when they cause long term changes and damage, the effects and the resultant alterations to your psyche, which unlike the drugs immediate effects are generally very unpleasant, are long lasting. It is why recovery from drug abuse can be so long and tortuous, and even recovered drug addicts may never return to how they once were.
  • The Proteus Effect — peoples' avatars in virtual worlds affect how they interact.
  • The physical transition period from childhood to adulthood is not an easy or pleasant one for most people.
  • This is the premise of the embodied mind thesis, which holds that all aspects cognition are influenced by bodily characteristics as innocuous as hand dominance.
  • Having one's stomach surgically reduced in size would seem like a purely physical change, the simple inability to eat as much as before. For some people that's what it works out to, with frustration resulting. For others it results in the feeling of having enough willpower to not consume as much, or just being less interested in food.
  • Sleep deprivation. It's something that everyone has experienced, and for an unfortunate many quite frequently, and even if you are not very aware on how you change when sleep deprived, you have probably seen how someone else who is sleep deprived who is usually calm or cheerful become cranky.
  • Certain aspects of one's personality can be affected majorly by the health of the bacteria in one's digestive system. Patients who have had to undergo serious procedures that result in their entire digestive tract being sterilized have been noted to have personality alterations. The easiest way to fix this is by transplanting someone else's gut fauna (usually in the form of capsulized feces, thankfully as a suppository and not oral pill) into the person - in some circumstances, the patient was then observed as behaving and acting like the donor for a little while. Thankfully, this has proven to only be temporary; the body memorizes how their gut fauna should be and after the donation settles in they'll return to their usual self as their body re-adapts the alien fauna to the native fauna.


Video Example(s):

Alternative Title(s): The Mind Is The Plaything Of The Body


Latex Dog

Dr. K shoots the human with a transfurring dart, that turns him into a dog-person and makes him lose his mind.

How well does it match the trope?

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Example of:

Main / TheMindIsAPlaythingOfTheBody

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