History Main / NinetyPercentOfYourBrain

* Referenced and subverted in ''Manga/IsekaiOjisan'': Uncle (having grown up in the nineties) believes this trope is true, and that unlocking it was the source of the power he obtained in the other world. Takafumi (having grown up in the twenty-tens and with easy access to the internet) immediately points out the trope was debunked long ago.

* [[Franchise/TheDCU DC Comics]] villain The Key once claimed to have tapped into "the ninety percent of the brain we never use" via a device he built, which allowed him to devise all manner of amazing plans and schemes. This is an aversion, though, as it also drove him completely mad, leading to the implication that he only THINKS he's tapping into new parts of his brain.

* Played straight in ''LightNovel/ACertainMagicalIndex'', as the eponymous character has a PhotographicMemory, and can only retain 1 year of memory in her mind, because 85% of it is taken up with an eidetic recollection of the [[NeuroVault complete contents of 103,000 spellbooks]]. That is, until it gets subverted with a sledgehammer when a professor reveals that the "15% left over for a year's memories" is complete BS and ''gives a proper explanation of how the mind works'' in the series. The main character even realizes he's been played for a fool when he does the math: if a year's worth of memories really took up 15% of your brain, you'd max out around age 7 and not be able to ever remember anything new.

This trope name comes from the oft-repeated but false assertion that humans only use 10 percent of their brains, a misquote of an foreword to Dale Carnegie's ''Literature/HowToWinFriendsAndInfluencePeople''.[[note]]"The average person develops only 10 percent of his latent mental ability."[[/note]] In RealLife, we use ''all'' of our brains, just not all at the same time -- in much the same way you don't have every electronic/mechanical item in your home running at all times; you only turn things on when you need to use them. If you ever do find yourself with every part of your brain "on" at once, congratulations, '''''[[BadNewsInAGoodWay you're having a seizure!]]'''''

This trope name comes from the oft-repeated but false assertion that humans only use 10 percent of their brains, a misquote of Dale Carnegie's ''Literature/HowToWinFriendsAndInfluencePeople''.[[note]]"The average person develops only 10 percent of his latent mental ability."[[/note]] In RealLife, we use ''all'' of our brains, just not all at the same time -- in much the same way you don't have every electronic/mechanical item in your home running at all times; you only turn things on when you need to use them. If you ever do find yourself with every part of your brain "on" at once, congratulations, '''''[[BadNewsInAGoodWay you're having a seizure!]]'''''

* Referenced and subverted in ''Manga/IsekaiOjisan'': Uncle (having grown up in the nineties) believes this trope is true, and that unlocking it was the source of the power he obtained in the other world. Takafumi (having grown up twenty-tens and with easy access to the internet) immediately points out the trope was debunked long ago.

** [[http://www.scp-wiki.net/scp-1475 SCP-1475]] of the Wiki/SCPFoundation is a deliberate {{Deconstruction}} (the author even flat-out stated that his inspiration for writing it was his [[PetPeeveTrope hatred of this trope]]). He gave himself a [[DisposableSuperheroMaker non-reproducible drug]] that lets him use 100% of his brain 100% of the time. This not only gave him [[MasterOfYourDomain complete control over his body]] but let him rewire his brain so that [[TheSleepless he doesn't need to sleep anymore]]. However, in a true case of BlessedWithSuck, this completely destroyed his autonomic nervous control (that is, the body's ability to automatically regulate the heart/lungs/etc.), so he has to spend most of his concentration on keeping himself alive. Not only does this not leave him much concentration to use his voluntary muscles, but he's also suffered permanent damage to a lot of his organs due to having messed it up in the past.

* ''Wiki/SCPFoundation'':

!!Examples:

[[folder:Literature]]
* ''Literature/TheImmortals'': Daine makes a reference to this in ''Wolf-Speaker'' while sharing the mind of a wolf whose brain was changed by association to her magic: "Numair had said, in an anatomy lesson, that humans used little of their brains... For Brokefang the difference was that each nook and cranny of his skull was packed with ideas."
* The Creator/DouglasAdams book ''Literature/TheLongDarkTeaTimeOfTheSoul'' plays with this: a character in a coma has a dream in which her mind is represented by an infinite collection of cabin trunks, of which ten percent contain past memories, and the remaining ninety percent contain [[EverythingsBetterWithPenguins penguins]].
* Comes up multiple times during ''Literature/TheDresdenFiles''. Harry Dresden's mental passenger Lasciel resides in the so-called "unused parts of Harry's brain.'' [[MrExposition Bob]] even quotes the 'ten percent' stat when they discuss it. All of this could be partially [[HandWave hand waved]] with the previously established plot element that Wizards have a different cellular biology than most, allowing for better healing and longevity. It's possible Wizards have abnormal neurology.
* Artemis's magic in ''Literature/ArtemisFowl: The Lost Colony'' is another case of this trope. Humans lost the kind of brainpower necessary for that long ago.
* Creator/RoaldDahl's ''Literature/{{Matilda}}''; the eponymous little girl gained access to psychic powers because she was willing to use more of her brain than the rest of her family was. It's all but stated, in the book, that this is a direct result of her not being intellectually challenged enough, since she [[spoiler:starts to lose her powers once she's moved up to sixth form]] at the end of the book. The same explanation [[spoiler:(but without power loss)]] is given in the FilmOfTheBook.
* Mark [=McHenry=] of ''Literature/StarTrekNewFrontier'' could not only use 100% of his brain, he could specify at any given time what percentage of his brain is dedicated to what activity. This is because [[spoiler:Mark isn't quite human, due to his being descended from the Greek God Apollo.]]
* In ''Literature/{{The Secrets of the Immortal Nicholas Flamel}}'', this is the basis for the idea of having one's powers "Awakened".
* ''Literature/TheZombieSurvivalGuide'' makes this same error in comparing zombies' senses to those of humans, speculating that undead without eyes have a "sixth sense" derived from the unused part of the brain. Oh, and it claims that we, the living, only use ''5%'' of our brains, doubling this trope's inaccuracy. As the claim is presented as being purely speculative regarding zombie abilities, it ''could'' be a case of an InUniverse error by the author.
* In ''[[Recap/DoctorWhoNewAdventuresAllConsumingFire All-Consuming Fire]]'', a character with psychic abilities (pyrokinesis, specifically) is discovered to have suffered a major head trauma that destroyed a large chunk of his brain. Bernice mentions the 90% thing, and speculates that the man's brain, in the course of rerouting around the damage, started using a previously unused part of the brain and activated the pyrokinesis.
* The Literature/EighthDoctorAdventures novel ''The Gallifrey Chronicles'' comes ''very close'' to getting this right... but doesn't.
-->There was an old myth that humans only used ten percent of their brains. This was a simple misunderstanding. Give or take, there was activity in every part of the human brain. But the physical structures were capable of ten times the activity they performed. It wasn't that a human being had a brain like a house with nine tenths of the rooms sealed off, it was more like a road network wasn't carrying as much traffic as they were designed to carry.
* In ''Literature/SmallGods'', Terry Pratchett said that the other 90 percent of the brain powers a sort of WeirdnessCensor so that the fact that the entire world we take for granted is, in fact, amazing, is ignored.
-->It is a popular fact that nine-tenths of the brain is not used and, like most popular facts, it is wrong. Not even the most stupid Creator would go to the trouble of making the human head carry around several pounds of unnecessary gray goo if its only real purpose was, for example, to [[BrainFood serve as a delicacy for certain remote tribesmen in unexplored valleys]]. It is used. And one of its functions is to make the miraculous seem ordinary and turn the unusual into the usual.\\\
Because if this was not the case, then human beings, faced with the daily wondrousness of everything, would go around wearing big stupid grins, similar to those worn by [[TheStoner certain remote tribesmen who occasionally get raided by the authorities and have the contents of their plastic greenhouses very seriously inspected]]. They'd say "Wow!" a lot. And no one would do much work.
:: From a certain point of view, this description is almost entirely accurate. A huge amount of brain power goes into basic data filtering and interpretation, all so that the relatively small part of our brains that does the thinking we're conscious of doesn't get overwhelmed. Show a person the raw data of their nerves and it would just look like static.
* The protagonist of ''[[http://www.gutenberg.org/files/32272/32272-h/32272-h.htm Insidekick]]'' by J. F. Bone develops psi powers (telepathy and teleportation), plus eidetic memory, after being invaded by a symbiont which activates a "large dormant portion" of his brain.
* In Stephen King's ''Literature/{{Cell}}'', the people who are hit by the Pulse lose almost all of their higher level reasoning skills. After this, [[spoiler: they slowly regain higher level thought, but they use unusual parts of their brain to do it, resulting in them developing telepathy and eventually telekinesis]]. Granted, this is just a hypothesis in-Universe, but the "we only use ten percent of our brains" myth gets thrown around a lot by some highly educated people.
* In ''Beneath the Dark Ice'', the protagonist's superhuman abilities are thought to have come from when he was shot in the head in a way that forced the brain to direct more blood to the areas of the brain with the most 'unknown functions'. How this accounts for super strength and endurance is not obvious.
* Creator/IsaacAsimov:
** ''Literature/FoundationSeries''' "Literature/TheMule": Part of the EmotionControl powers that the Mule had was to [[BottledHeroicResolve cause intuition and creativity to skyrocket, at the expense of their lives]]. He describes human brains as normally operating at 20% efficiency (essentially failing to use 80%), and he can use his power to force all of it to work ''non-stop'' without any chance to rest for weeks on end.
** ''Literature/PebbleInTheSky'': The main character, who has [[AccidentalTimeTravel inadvertently been pushed forward from our time]] to the far future setting of the novel, gets an experimental "Synapsifier" treatment in the hope it will help him learn the language. It does that and more ... he starts becoming telepathic, and strongly enough so that at one point he kills one of the bad guys that way, without even intending to. Played with in that the novel makes quite clear ''why'' humans only use a small percentage of their brain at any one time (within the context of the setting): [[ExplosiveOverclocking using more is damaging to the person in question]], to fatal levels (partly because once the Synapsifier has been used on a person, the effect is permanent). Evidently those ninety percent are there to keep the brain running for year after year.
* ''Literature/MyTeacherIsAnAlien'': In the second {{Novel}}, one boy, a school bully of below-average intelligence, has his brain "fried", which makes him a genius and a [[{{Telepathy}} telepath]]. In the third, the aliens remove the protagonist's brain temporarily to study why humans have the most powerful, yet under-utilized, brains in the galaxy. [[spoiler:It's part of our unconscious HiveMind. Turns out we used to use it all, but as humanity spread the sheer amount of psychic chatter overwhelmed the conscious mind, and so humans suppress it so we can stay sane.]]
* Creator/DavidGerrold's novel ''Literature/WhenHarlieWasOne'': Mentioned as the supposed "reason" why the sentient computer of the title, despite being like a human brain, is so much more efficient.
* Creator/DesmondWarzel: In the short story [[http://sfreader.com/contest-2008-1.asp "On a Clear Day You Can See All the Way to Conspiracy"]], a caller to a radio show invokes the "ten percent" myth and the host smacks him down, even giving the "seizure" explanation mentioned in the introduction above.
* ''Literature/TheNameOfTheWind'' explains its magical naming system by drawing a line between the waking mind and the sleeping mind, with the sleeping mind being more powerful and more knowledgeable but difficult to access.
* Mentioned and immediately debunked in ''Literature/RunProgram''. The person debunking it compares it to a car driving on a highway. If it was operating at 100% capacity, then ''every single system would be on at the same time''. Imagine wipers constantly working, both the gas and the brake pedals floored, with every single gear engaged (including the reverse), and doors constantly opening and closing. That would be our brains at 100%.
* The operating premise of the ''[[Franchise/TransformersGeneration1 Transformers]]'' [[{{Gamebooks}} interactive book]] ''Project Brain Drain''. The Decepticons plan to drain the awesome untapped mental energies of the human brain from the attendees of a rock concert.
* In ''Literature/TheDestroyer'', it's been mentioned that Sinanju allows you to use more of your brain, which in turn allows you to do incredible stuff.
* In Creator/DanielPinkwater's ''Literature/AlanMendelsohnTheBoyFromMars'', the Klugarsh Mind Control course claims that only 10% of your brain is in use, and that the secret to telepathy, telekinesis, etc is learning to access the rest of your brain.
* The psychic villain of the ''Literature/FearStreet'' novel ''One Evil Summer'' at one point claims, "You know, they say people use only a small portion of their brains. Well, I use all of my brain. I can do anything. Anything!" Of course, she is kind of insane...
* In ''Literature/DiaryOfAWimpyKid: Double Down'', Greg hears that humans only use 90% of their brains. He hopes that people don't figure out how to get the last 10%, imagining it being complete chaos.
* In ''Literature/WhenRabbitHowls'', Ten-Four opines that people only use 10% of their brains and 3% of their physical energy due to being so sedentary. The theory throughout the book that people with multiple personalities all start as super-intelligent children was popular at the time. [[note]]This is also sloppy interpretation; [[Film/{{Sybil}} Dr. Cornelia Wilbur]] said she personally had never met a multiple who was not highly intelligent, and that became "all multiples are geniuses" in the popular imagination and even among doctors who should have known better.[[/note]]

[[folder:Live-Action TV]]
* ''Series/MyFavoriteMartian'': Cited by "Uncle Martin" as one of the reasons Martians are so much more advanced and intelligent than human beings. Martians use all of their brains, while earthlings only use a small percentage of theirs.
* ''Series/{{Alphas}}'': Stanton Parrish has a variation of this: He has the ability to consciously control every process in his brain, even those that are not consciously controlled in ordinary humans. This makes him able to instantly recover from any injury and prevents him from aging. However, it comes with several downsides: His emotional relationships with others are disrupted, making him similar to a [[TheSociopath sociopath]] and his ability to retain memories is disrupted to an extent (likely due to the fact that his brain, powerful as it is, still lacks the capacity to hold over 200 years worth of memories all at once.)
* Johnny's powers in the television version of ''Series/TheDeadZone'' come from the fact that a normally unused part of his brain became active to compensate for a damaged section.
* Referred to in the {{premiere}} of ''Series/{{Heroes}}'' as an example of one way humanity might make a sudden evolutionary leap, but then mercifully dropped. Only to be brought back up in season three, in a speech by Sylar.
* ''Series/{{Eureka}}'''s scientific adviser was on record as making sure that when that concept was used on the show, the line was "ten percent... at any one time" specifically to dodge this trope.
* ''Franchise/StargateVerse'': The idea that 90% of the brain is unused becomes a major plot point of the Ascension MythArc within both ''Series/StargateSG1'' and ''Series/StargateAtlantis''. To be able to AscendToAHigherPlaneOfExistence without the aid of an already-Ascended being, the brain must become fully active. As the human brain activates an increasing percentage of the brain, they begin to develop special abilities, such as the ability to [[HealingHands heal with a touch]], or [[{{Telepathy}} read minds]] or [[MindOverMatter move objects with the mind]]. Usually, such a human will only develop a single ability, but as they get closer to the threshold for Ascension, they begin to display multiple abilities. In ''SG-1'', the Goa'uld are ever in search of powerful hosts to parasitise, so a rare few have experimented with technology to force humans to develop these abilities or even to actually be capable of taking a Goa'uld into Ascension. ''Atlantis'' expands on ''SG-1'' when an ancient technological device is found that's supposed to help people artificially reach Ascension by forcibly and gradually awakening the inactive 90%. The catch is that this isn't how the brain is supposed to naturally function and it therefore brings the modified human to the point of permanent seizure. The machine therefore forces the modified human to either Ascend or die.
* Referred to in ''Series/KyleXY''. The titular Kyle has a highly advanced brain, learning to speak in one day, and learning kung fu and Chinese from watching an old Bruce Lee movie. They give him a CAT scan and the scan showed he used 80% of his brain. However, the doctors noted this as strange, citing the problems one would have at such levels (such as seizures), and wrote it off as a machine malfunction. It is later shown that if he uses his powers too much, he will get a seizure.
* ''Series/JohnDoe'' actually acknowledges that only about 10% is in use at any given time but implies that tapping into the other 90% at the same time is what allows some of the characters to use their psychic abilities.
* In ''Series/{{Seinfeld}}'', when George stopped having sex, his brain was free to do other things, accounting for his sudden burst of knowledge. Jerry compared George's brain to a cabbage, with a tiny leaf being the part he normally devoted to anything that wasn't sex. This seems to work the opposite way for women (as shown with Elaine's sudden stupidity), by which Jerry meant that most of men's brainpower is normally invested toward obtaining sex, while a woman always has men available to take care of her sexual needs ''for'' her and never has to think about it herself; therefore a celibate man becomes super-intelligent since his brain is freed up, while a celibate woman becomes super-stupid since she loses all her brainpower into thinking about sex.
* In ''Series/{{Fringe}}'', the 10% fallacy is averted only to be replaced with a different (even more absurd) rationalization. [[spoiler:A MadScientist several decades in the past developed a drug that prevents babies from losing the natural potential they have at birth.]] In a DoubleSubversion the MadScientist in question fails completely in clinical trials only to be proven right when [[spoiler:Olivia]] develops psychic powers. Maybe.
** Another subversion on that show: The reason Walter is mentally askew is that [[spoiler:10% of his physical brain was removed and implanted in other people's brains, giving them all bits and pieces of a complex design, in a bit of Lego brain surgery. Getting back that 10% puts him on track to solving an important puzzle]].
* In the last episode of ''Series/LoisAndClark'', Dr. Mensa uses the rest of his brain and gets [[MyBrainIsBig an enlarged brain]], the power of mind control and the moniker "Fat Head".
* The main plot line for an episode of ''Series/HoneyIShrunkTheKids''. To make matters sillier, accessing the other 90% gave the character in question godlike powers. All this was caused by a device that was established in a previous episode to be used for [[FreakyFridayFlip brain-swapping]].
* In ''Series/StarTrekDeepSpaceNine'', this is cited as why Dr. Bashir can lose a portion of his brain and be completely fine (this was before Bashir was {{Retcon}}ned to be super-intelligent.) It's absolutely not true and is in fact one of the ways we know the 10% thing is a myth; there is almost no part of the brain we can lose without suffering loss of ability.
* Spoofed in an Italian RealTrailerFakeMovie parody of ''Limitless'', mercilessly titled ''Italiano Medio'' (''[[SelfDeprecation Average Italian]]'').
-->'''Protagonist's friend:''' You know that story, that we use only twenty percent of our brain? ''[hands him pill]''\\
'''Protagonist:''' OK, I'll try it just out of curiosity. ''[swallows pill]''\\
'''Protagonist's friend:''' With this, you'll only use ''two percent''.
* Disproven on ''Series/{{Mythbusters}}'', Tory's brain scans showed him using 15-30% of his brain, depending on what he was doing.
* Referenced in episode 5 of ''Series/AlmostHuman'' where an alleged [[ISeeDeadPeople spirit medium]] says her powers are the result of the Cerebellux procedure, which enhances use of brain pathways.
* Referenced in the first episode of ''Series/TwelveMonkeys'', when scans of Cole's brain reveal that he's using the entirety of his brain. In a twist, the researchers point out that this ''should'' be a Grand Mal seizure, except it's somehow organized and controlled, turning him into a human computer calculating something obscenely complex. They don't know what he's calculating, but the audience knows that he's a time traveler who has been modified to survive the journey, implying that this is part of the process.
* {{Defied|Trope}} on ''Series/AgentsOfSHIELD'', where Dr. Holden Radcliff explains that it's a myth that we only use 10% of our brains.
* ''Series/NightMan'': When Johnny Domino gets struck by lightning and starts hearing other people's thoughts, this is the explanation offered by the medical consultant on psychic phenomena--who's apparently been spearheading our side of an ESP race with the Soviet Union.
* ''Series/BirdsOfPrey2002'': Barbara claims that ordinary humans use only five percent of their brains, but metahumans far more. Dinah uses fifty percent, her scans reveal.
* Discussed and defied in ''Series/{{Limitless}}''. [[spoiler:Brian attends a party where everyone there is on low-grade NZT]]. He hears someone saying that you only use ten percent of your brain and that the pill works by allowing you to use more. Brian responds by pointing out that it's a myth.
* Surprisingly played straight in the episode "[[Recap/BlackMirrorBlackMuseum Black Museum]]" of ''Series/BlackMirror''. In the second segment, a man is informed that human beings use only 40% of their brains, so they could [[BrainUploading upload]] the consciousness of his comatose girlfriend into the "empty space" of his own brain, allowing her mind to "take the passenger's seat" on his mind. It [[GoneHorriblyWrong ends badly]].

[[folder:Music]]
* In the Music/LesLuthiers play ''Manuel Darío'', one of the people that is interviewed about the titular character is a psychologist. He has a theory in that people waste 50% of their mental capacity, and that [[StealthInsult Manuel Darío was mentally gifted]] ([[UnreliableNarrator or at least it's what Manuel Darío thought he said]]) because he wasted '''100%''' of his mental capacity.

[[folder:Tabletop Games]]
* ''TabletopGame/{{Aberrant}}'' uses this as part of the MetaOrigin for novas. Most humans have an underdeveloped, uncharted node in their brain that maps the background forces of the universe. When a nova Erupts, this node becomes active, allowing for limited manipulation of reality -- a.k.a., superpowers.
[[/folder]]

[[folder:Video Games]]
* In ''VisualNovel/ChaosHead'', Norose muses that Gigalomaniacs use the remaining 90% of their brain unlike normal humans, and this is responsible for their abilities. And possibly even worse, it's also stated that 80% of the brain is used for processing visual data.
* ''Franchise/AssassinsCreed'' makes use of this trope to explain where the accumulated memories of ancestors that all humans have in its universe are being stored. It also uses it to explain Eagle Sense and Eagle Vision, extranormal senses that only some people [[spoiler:with a greater than usual concentration of DNA from the AbusivePrecursors]] can learn to use.
* This is given as the reason why Fuka, a human [[OrdinaryHighSchoolStudent Ordinary Middle School Student]], can keep up with her demon teammates in ''VideoGame/Disgaea4APromiseUnforgotten''. She deluded herself into thinking the afterlife is AllJustADream, and since it's her dream, she's free to do anything she wants. This allows her brain to unlock her full potential.
* In ''VideoGame/DragonBallOnline'', set more than 200 years after the main series, this happened with the book "Groundbreaking Science" written by Gohan, explaining Ki manipulation to the saiyan blooded humans.
[[/folder]]

* The famous [[http://en.wikipedia.org/wiki/Phineas_Gage Phineas Gage]] had a tamping rod driven clean through his head after he struck it with a sledgehammer when too much gunpowder had been poured into its hole, causing massive damage to his frontal lobes. He recovered, memories and abilities mostly intact, but with a radically changed personality-friends and family said he was "no longer Gage." Despite the injury, he managed to live for another twelve years. He was long used as an example of the effects of damage to the frontal lobs on a person, but the severity of his personality changes are now questioned due to a lack of actual records of what he was like from before the accident.
* There is a famous case of a character who came to a doctor complaining of headaches, and turned out on the X-rays to have no cerebellum. Apparently, he'd been born without one, and the cerebrum had simply taken over all the necessary tasks-to such success that he was working as a steeplejack!

* [[http://www.scp-wiki.net/scp-1475 SCP-1475]] of the Wiki/SCPFoundation is a deliberate {{Deconstruction}} (the author even flat-out stated that his inspiration for writing it was his [[PetPeeveTrope hatred of this trope]]). He gave himself a [[DisposableSuperheroMaker non-reproducible drug]] that lets him use 100% of his brain 100% of the time. This not only gave him [[MasterOfYourDomain complete control over his body]] but let him rewire his brain so that [[TheSleepless he doesn't need to sleep anymore]]. However, in a true case of BlessedWithSuck, this completely destroyed his autonomic nervous control (that is, the body's ability to automatically regulate the heart/lungs/etc.), so he has to spend most of his concentration on keeping himself alive. Not only does this not leave him much concentration to use his voluntary muscles, but he's also suffered permanent damage to a lot of his organs due to having messed it up in the past.

* Creator/RoaldDahl's ''Literature/{{Matilda}}''; the eponymous little girl gained access to psychic powers because she was willing to use more of her brain than the rest of her family was. It's all but stated, in the book, that this is a direct result of her not being intellectually challenged enough, since she [[spoiler:starts to lose her powers once she's moved up a grade]] at the end of the book. The same explanation [[spoiler:(but without power loss)]] is given in the FilmOfTheBook.
** This could be more of a jab at Matilda's family, since they aren't exactly the brightest bulbs in the shed. The trope isn't actually invoked at any point.

* ''Manga/FistOfTheNorthStar'' does something similar with ''breathing''. The real secret to Kenshiro's CharlesAtlasSuperpower is harnessing the traditionally untapped 70% of his breathing. The Ripple in ''Manga/JoJosBizarreAdventure'' works that way, too.

* {{Parodied|Trope}} in ''Script/AHDotComTheSeries'', episode "The Narcissus Syndrome":
-->'''Thande:''' You know how we only use ten percent of our brain capacity?\\
'''Torqumada:''' No, because that's a ridiculous urban myth.\\
'''Thande:''' Shut up, I'm trying to [[LiesToChildren explain something]] to the unscientific Muggles here.

* ''Series/JohnDoe'' actually acknowledges that only about 10% is in use at any given time, but implies that tapping into the other 90% at the same time is what allows some of the characters to use their psychic abilities.

* In ''Series/{{Fringe}}'', the 10% fallacy is averted only to be replaced with a different (even more absurd) rationalization. [[spoiler: A MadScientist several decades in the past developed a drug that prevents babies from losing the natural potential they have at birth.]] In a DoubleSubversion the MadScientist in question fails completely in clinical trials only to be proven right when [[spoiler: Olivia]] develops psychic powers. Maybe.
** Another subversion on that show: The reason Walter is mentally askew is that [[spoiler: 10% of his physical brain was removed and implanted in other people's brains, giving them all bits and pieces of a complex design, in a bit of Lego brain surgery. Getting back that 10% puts him on track to solving an important puzzle.]]

* The main plot line for an episode of ''Series/HoneyIShrunkTheKids''. To make matters more silly, accessing the other 90% gave the character in question godlike powers. All this was caused by a device that was established in a previous episode to be used for [[FreakyFridayFlip brain-swapping]].
* In ''Series/StarTrekDeepSpaceNine'', this is cited as why Dr. Bashir can lose a portion of his brain and be completely fine (this was before Bashir was {{Retcon}}ned to be super-intelligent.) It's absolutely not true, and is in fact one of the ways we know the 10% thing is a myth; there is almost no part of the brain we can lose without suffering loss of ability.

* [[DefiedTrope Defied]] on Series/AgentsOfSHIELD, where Dr. Holden Radcliff explains that it's a myth that we only use 10% of our brains.

* Surprisingly played straight in the episode [[Recap/BlackMirrorBlackMuseum Black Museum]] of ''Series/BlackMirror''. In the second segment, a man is informed that human beings use only 40% of their brains, so they could [[BrainUpload upload]] the counscience of his comatose girlfriend into the "empty space" of his own brain, allowing her mind to "take the passanger's sit" on his mind. It [[GoneHorriblyWrong ends bad]].

[[folder:Web Comics]]

* Parodied in ''Webcomic/ScaryGoRound'', where a man survives having 90% of his brain eaten by a zombie because by incredible coincidence she ate only the 90% that no one uses.

** Later, in [[http://www.egscomics.com/index.php?id=2106 the main strip,]] an Immortal starts telling a series of BlatantLies in order to demonstrate to a confused griffon that Immortals are capable of lying. This is one of them.

-->'''Hijack''': Well, the brain is like a muscle, and you only use 10% of your brain. But I'm 100% brain, so-
-->'''Max''': [[SuddenlyShouting GOD, SHUT UP, I HATE YOU]]

* A Website/{{Cracked}} article compares this notion to becoming a better writer by using every key on your keyboard in every sentence.
* Parodied in ''Script/AHDotComTheSeries'', episode "The Narcissus Syndrome":

* [[http://www.scp-wiki.net/scp-1475 SCP-1475]] of the Wiki/SCPFoundation is a deliberate {{Deconstruction}} (the author even flat-out stated that his inspiration for writing it was his [[PetPeeveTrope hatred of this trope]]). He gave himself a [[DisposableSuperheroMaker non-reproducible drug]] that lets him use 100% of his brain 100% of the time. This not only gave him [[MasterOfYourDomain complete control over his body]], but let him rewire his brain so that [[TheSleepless he doesn't need to sleep anymore]]. However, in a true case of BlessedWithSuck, this completely destroyed his autonomic nervous control (that is, the body's ability to automatically regulate the heart/lungs/etc), so he has to spend most of his concentration on keeping himself alive. Not only does this not leave him much concentration to use his voluntary muscles, he's also suffered permanent damage to a lot of his organs due to having messed it up in the past.

* [[http://www.villainsource.com/ Villain Source]] sells brain pills that are guaranteed to increase your IQ by 300% or your money back! (The small prints adds that if you believe this, then you really need those pills).

--> "If you really think someone could scoop out 90% of your brain, and you'd be alright, then perhaps you really do only use ten percent of it"

* Surprisingly played straight in the episode [[Recap/BlackMirrorBlackMuseum Black Museum]] of ''Series/BlackMirror''. In the second segment, a man is informed that human beings use only 40% of their brains, so they could [[BrainUpload upload]] the counscience of his comatose wife into the "empty space" of his own brain, allowing her mind to "take the passanger's sit" on his mind. It [[GoneHorriblyWrong ends bad]].

* Surprisingly played straight in the episode [[Recap/BlackMirrorBlackMuseum Black Museum]] of ''Series/BlackMirror''. In the second segment, a man is informed that human beings use only 40% of their brains, so they could [[BrainUpload upload]] the counscience of his deceased wife into the "empty space" of his own brain, allowing her mind to "take the passanger's sit" on his mind. It [[GoneHorriblyWrong ends bad]].

* In ''Film/MyFavoriteMartian'', Uncle Martin states that Martians earn their powers from fully using their brains. Tim disagrees, and the reply is "[[InsaneTrollLogic Your astronauts pee in their spacesuits. Case closed.]]"

* Referred to in ''Series/KyleXY''. The titular Kyle has a highly advanced brain, learning to speak in one day, and learning kung fu and Chinese from watching an old Bruce Lee movie. They give him a CAT scan and the scan showed he used 80% of his brain. However, the doctors noted this as strange, citing the problems one would have at 100% brain usage (such as seizures), and wrote it off as a machine malfunction. The audience and the character Josh know it's not a malfunction. It is later shown that if he uses his powers too much, he will get a seizure.

* Creator/ValiantComics invoked this with the [[DifferentlyPoweredIndividual Harbingers]], people with StockSuperpowers. Unlike their [[{{Mutant}} equivalents]] in some other comic universes, Harbingers are not physically different from other humans. Elevated levels of activity in their brains result in [[PsychicPowers psionic abilities]] that give them their powers. Ordinary humans can duplicate Harbinger powers through the use [[AppliedPhlebotinum special cybernetic brain implants]].

* There are plenty of jokes referring to people ''[[InvertedTrope without any brain at all]]'' working as [[AcceptableProfessionalTargets politicians, lawyers, and the like]].

This trope name comes from the oft-repeated but false assertion that humans only use 10 percent of their brains, a misquote of Dale Carnegie's ''Literature/HowToWinFriendsAndInfluencePeople''.[[note]]"The average person develops only 10 percent of his latent mental ability."[[/note]] In RealLife, we use ''all'' of our brains, just not all at the same time -- in much the same way you don't have every electronic/mechanical item in your home running at all times; you only turn things on when you need to use them. If you ever do find yourself with every part of your brain "on" at once, congratulations '''''you're having a seizure.'''''

* Mentioned in ''Webcomic/{{Paranatural}}'', [[https://www.paranatural.net/comic/chapter-5-page-258 during a battle]] with their teacher possesed by [[BodySurfer Hijack]] (a spirit shaped like a brain). When [[DeadpanSnarker Max]] complains that Hijack has too many abilities, he used this mixed with InsaneTrollLogic.