Struck by a radioactive* seizure, Peter Parker gained the ability to use proportional amounts of his brain!
"[This myth is] one of the hardiest weeds in the garden of psychology."
— Donald McBurney, neuropsychologist
Situation where a character's miraculous abilities are not so much a product of "superpowers" as it being an ability humans in the series universe could have but are unable to access for some reason. That is, until they reach Brain Critical Mass
. Very prevalent in Sci Fi
as a common trope with mentalists and ESP'ers.
This trope name comes from the oft-repeated but false assertion that humans only use 10 percent of their brains. We use all of our brains, just not all at the same time — in much the same way that hitting a few specific notes on a piano will produce a beautiful tune, whereas mashing them all at the same time would only create a crashing cacophony.
There are occasions in some people's lives in which the entire brain fires up at once. They're called seizures.note
For exceeding the limitations of the body to epic effect, see Charles Atlas Superpower
. Also see Pineal Weirdness
, which tends to show up in similar places.
This trope was examined by
, throwing the 10% theory right out the window when it was proven that the human brain is at least 15% active while sleeping
, and even more-so when awake.
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Anime and Manga
- AKIRA has Tetsuo and the Espers, who have crazy mental abilities due to this trope. It's implied that the rest of humanity has the same potential, but it goes unrealized.
- In Dragon Ball, all humans have the potential to fly and shoot energy beams - if they are lucky enough to find someone who can teach them how to use Ki energy. In Dragon Ball Online, set more than 200 years after the main series, this happened with the book "Groundbreaking Science" written by Gohan, explaining Ki manipulation to the general public.
- The Night Head Genesis anime states at the start that normal people leave 70% of their brain unused. Once again, this explains psychic powers.
- Fist of the North Star does something similar with breathing. The real secret to Kenshiro's Charles Atlas Superpower is harnessing the traditionally untapped 70% of his breathing. The Ripple in JoJo's Bizarre Adventure works that way, too.
- The Stone Mask-created vampires in JoJo's Bizarre Adventure gain their power through the activation of unused parts of the brain via acupuncture. This awakens the human's evolutionary potential (with abilities like Wall Crawling, liquid eye beams, superspeed/strength, regeneration, sucking blood through their fingers, and creating zombies) and it inverts the lifeforce energy in their bodies (making them undead-like beings weak to sunlight and Ripple, the amplified essence of life)
- Played straight in To Aru Majutsu no Index as the eponymous character can only retain 1 year of memory in her mind, because 85% of it is taken up with an eidetic recollection of the 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. Cue Crowning Moment of Awesome as the hero realizes that he's been played for a sucker.
- Mobile Suit Gundam's Universal Century:
- Char's Counterattack (where it is mentioned) may use this explanation for why Newtypes exist—that people used only a part of their brains on Earth, and began to use the rest after moving into space. However, it was said to be "half" of the brain being used, not 10%. Also the conversation was between a couple of teenagers, so they may simply not know what they're talking about (they also take a fairly romantic interpretation of the idea/purpose of Newtypes, which Gundam goes back and forth on).
- This first appeared in the writings of Zeon Zum Deikun, inventor of the Newtype concept, in the Mobile Suit Gundam novelizations.
- This is in turn based on the writings Timothy Leary, specifically the 8-Circuit Model of Consciousness which predicted that people's brains would develop in new ways in the future, becoming more enlightened to cope with the challenges of space travel.
- The foundation of superpowers in Needless.
- In an episode of Katekyo Hitman Reborn!, Reborn gives Gokudera an unique brand of Training from Hell by making him eat ramen while withstanding I-pin's Gyoza-ken. Reborn's technical explanation is that, since the Gyoza-ken affects directly the brain, the fact of being able to eat ramen while resisting the muscular spasms the technique provokes would force Gokudera to use all of his brain capacity (whose standard usage is defined here as 30%).
- This is part of the premise for Psyren. Like many others, this explains psychic powers, though they seem no less limited than any other set of superpowers in other series.
- Deathstroke, a.k.a. Slade, from Teen Titans, has this as one of his powers (though it's not stated outright in the series, only the comics). Later retconned in that he uses his brain in various ways that regular humans do not. His grey matter got re-routed and reprogrammed. Makes slightly more sense - at least in terms of comic book science.
- According to Todd Ingram in Scott Pilgrim, ninety percent of your brain is filled up with curds and whey. Hence his telekinetic vegan power. Arguably an aversion, though, as Todd is shown to be the dimmest and least imaginative of the League of Evil Exes. While it is canon that veganism gives psychic powers in the Pilgrim universe, Todd's explanation comes off more like a thinly-veiled insult, and Kim in particular seems skeptical.
- Also, when he's revealed to have broken the rules of veganism, he had his powers taken by the "vegan police".
- This fake statistic appeared in the Iron Man mini "Hypervelocity", as the AI protagonist was frustrated at being forced to function at a relatively slow "cognitive clockspeed".
- 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.
- An odd Superman story featured a stand-up comedian having part of his unused brain areas activated in an accident, which gave him telekinetic powers, which he used unconsciously to become a sand-covered monster that tried to amuse people to counter his fear of not being laughed at. He was only cured once Superman used his super laughter so that he could finally hear through all the sand that someone was laughing. Okay?
- This is part of the plot of the 1986 film Flight of the Navigator, where a young boy discovers an alien probe had experimented with using the unused ninety percent of his brain for data storage.
Max: Back on Phaelon, we discovered that your inferior species uses only ten percent of your brain. So we filled it all the way up with star charts to see what would happen.
David: What happened?
Max: It leaked.
- Richard uses this as an insulting mnemonic device to help Tommy Boy remember the figure 1.5%.
Richard: "Let's say the average person uses 10% of their brain. How much do you use? 1.5%. The rest is clogged with malted hops and bong resin."
- Besides the milk-white complexion and hairlessness, this is what made the protagonist of the film Powder so special.
- Pretty much how Extremis is applied in Iron Man 3. Aldrach, through years of research, has found that the human brain has an empty space, hinting that humanity is not at the apex of evolution.
- The Last Mimzy does this; their newly-unlocked abilities include telepathy, telekinesis, and super-hearing, as well the ability to control spiders by emitting certain frequencies, to send objects through small warp portals, and to draw ancient patterns without ever having seen or heard of them. In the future, levitation is also a standard part of humanity's milieu.
- It is implied in Phenomenon that the incredible mental and psychic abilities John Travolta's character, George, suddenly gains after seeing a strange light in the sky is caused by a tumor spreading across his brain and activating unused parts of it. Also, killing him.
- In Defending Your Life, everyone on Earth is said to use 3-5% of their brains. When a person dies and goes through the Celestial Bureaucracy, they have the chance to move up to the next level, where it's possible to use more of their brain. Then after that lifetime, they have the chance to move up to the next level and so on; each level allows one to use more and more of one's brain, which means being more intelligent and less afraid.
- Referenced for the sake of a joke in Wedding Crashers. "You know how they say we only use ten percent of our brains? I think most people only use ten percent of their hearts."
- In My Favorite Martian, Uncle Martin states that Martians earn their powers from fully using their brains. Tim disagrees, and the reply is "Your astronauts pee in their spacesuits. Case closed".
- The Sorcerer's Apprentice uses this trope straight to describe how sorcerers get the powers.
- Inception says this is why in dreams your brain can work faster, as the majority of your brain's processing ability is devoted to processing sensory perceptions. With the use of shared dreaming technology, the brain can work much faster, allowing for a dreamworld hour to pass in minutes in the real world.
- In Scott Pilgrim vs. the World vegan evil ex-boyfriend Todd Ingram claims the source of his psychic powers is that he's able to use more than 10% of his brain because isn't gunked up with all that filthy animal protein. Brain is made out of animal protein, but given that Todd also says that he does not know the meaning of the word "incorrigible" and he does not, this creates reasonable doubt of the credibility of his claim.
- Of course, he loses his powers not because he violated the vegan diet but because the Vegan cops took them away. This pretty much negates his claim.
- In My Stepmother is an Alien the alien Celeste explains that "We use 104% of our brain capacity, as opposed to your 36%."
- In the 2009 film Race to Witch Mountain, the extraterrestrial humans Sarah and Seth have access to telekinesis, telepathy, and phasing, which Sarah states the humans on Earth can not use yet, because they "haven't learned to use that part of [their] brain yet." Ironically, in an interview with AnnaSophia Robb, who plays Sarah, she confirmed that the director wrote that line in because he wanted to be "as scientifically accurate as possible."
- In the film Limitless, starring Bradley Cooper and Robert DeNiro, Cooper plays a down-on-his-luck writer who takes a smart drug called NZT-48 that allows him to access 100% of his brain as opposed to "the twenty percent", granting him superhuman intelligence and prescience.
- Implied in The Shadow, in the end, the Big Bad gets a spike through his head and has to have a part of his brain that "no one uses" removed. It turns out that this was where his psychic powers were located.
- 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 Douglas Adams book The Long Dark Tea-Time of the Soul 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 penguins.
- Subverted during the climax of Jim Butcher's White Night. Harry Dresden's mental passenger Lasciel temporarily over-clocks his brain in order to gain additional time to react to a threat. It is made clear that this is a very Bad Idea and will likely result in brain damage if done for an extended period of time.
- Commented upon and played straight multiple times in the series, Lash even resides in the so-called "unused parts of Harry's brain".
- Bob even quotes the 'ten percent' stat when they discuss it, though! So it's played completely straight, even though the brain speedup is a Bad Thing.
- Even worse, this overclocking is normal in stressful situations. It can happen to normal humans during dangerous periods, for exactly the purpose of giving them a smaller reaction time. More here.
- Artemis' magic in Artemis Fowl: The Lost Colony is another case of this trope. Humans lost the kind of brainpower necessary for that long ago.
- Roald Dahl's 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 starts to lose her powers once she's moved up a grade at the end of the book. The same explanation (but without power loss) is given in the Film of the Book.
- 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.
- Mark McHenry of Star Trek: New Frontier 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 Mark isn't quite human, due to his being descended from the Greek God Apollo.
- Comes up in Starfighters of Adumar, but context makes it pretty clear that this is a joke. Wes is known for being somewhat immature, and he tells Wedge that he thought he heard something last night, when Wedge was... getting lucky.
Wedge: "That old lack of oxygen thing will get you every time. How much brain damage did you suffer? [...] And, more importantly, was it to any of the parts of your brain that you use, or was it in the majority portion?"
- In The Secrets of the Immortal Nicholas Flamel, this is the basis for the idea of having one's powers "Awakened".
- The Zombie Survival Guide 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.
- The Doctor Who Expanded Universe 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 Small Gods, Terry Pratchett said that the other 90 percent of the brain powers a sort of Weirdness Censor so that the fact that the entire world we take for granted is, in fact, amazing, is ignored.
- The protagonist of Insidekick by J. F. Bone develops psi powers (telepathy and teleportation), plus eidetic memory, after being invaded by a symbiote which activates a "large dormant portion" of his brain.
- In Stephen King's Cell, the people who are hit by the Pulse lose almost all of their higher level reasoning skills. After this, 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 theory 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.
- The Mule from Foundation could use an intellect Explosive Overclocking power on others (cause intuition and creativity to skyrocket, but has bad effects on the one it is used on). The way it is described, it seemed less about using new parts of the brain, and more about using all of it non-stop without any chance to rest for weeks on end, but he, himself, mentioned a normally low efficiency (20%) as an explanation. This could be attributed him having "education, that of the tramp worlds, and the backwash alleys of space."
- In Isaac Asimov's Pebble in the Sky, the main character, who has inadvertently been pulled forward from our time to that of the novel, during the Galactic Empire period that leads up to the Foundation books, 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 novel makes quite clear why humans only use a small percentage of their brain at any one time: using more is damaging to the person in question, to fatal levels (partly because, as opposed to the Mule's power mentioned above, 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.
- This is a big part of the plot of the My Teacher Is An Alien series. In the second installment, one boy, a school bully of below-average intelligence, has his brain "fried" to make him a genius and a telepath. In the third, the aliens remove the protagonist's brain temporarily to study it. The reason is that humans have the most powerful, yet under-used, brains in the galaxy, and the aliens are trying to figure out why we suppress our supposedly vast mental powers.
- It's part of our unconscious Hive Mind. 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 to stay sane.
- This is one of the major things that separate immortals like Daetrin from the Marra in The Madness Season. When Daetrin transforms into a wolf, brain scans show him to have neural processes similar to those of a wolf. When Marra does the same thing, her entire brain is lit up, which the scientists exclaim would be impossible normally.
- No, they were amazed at Kiri's scans because she used only the parts that were needed to keep her body upright and mobile (motor control, autonomics, language processing) and used them extremely intensely. Everything else was left utterly untouched, because non-corporeal entities like the Marra don't need their meat puppets to handle memory and cognition, they do that on their own.
Live Action TV
- Johnny's powers in the television version of The Dead Zone 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 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.
- 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.
- Stargate SG-1 and Stargate Atlantis have several instance where this comes up and is dodged in the same manner that Eureka does — by upping the percentage used at a time, rather than overall. Increasing the amount used to almost 100% is one of the criteria to Ascend to a Higher Plane of Existence (or at least, it's required for doing so without somebody who's already ascended helping you).
- One Atlantis episode involves a device that artificially boosts brain activity in order to facilitate ascension. Which proved problematic because the human brain isn't supposed to function that way: eventually it would have basically caused a permanent seizure, so once brain activity got to the ascension threshold, it was basically a matter of "ascend or die."
- Referred to in Kyle XY. 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 by being Genre Savvy. It is later shown that if he uses his powers too much, he will get a seizure.
- John Doe 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 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; therefore a celibate man becomes super-intelligent since his brain is freed up, while a celibate woman loses all her brainpower into thinking about sex.
- In Fringe, the 10% fallacy is averted only to be replaced with a different (even more absurd) rationalization. A Mad Scientist several decades in the past developed a drug that prevents babies from losing the natural potential they have at birth. In a Double Subversion the Mad Scientist in question fails completely in clinical trials only to be proven right when Olivia develops psychic powers. Maybe.
- Another subversion on that show: The reason Walter is mentally askew is that 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 Lois and Clark, Dr. Mensa uses the rest of his brain and gets an enlarged brain, the power of mind control and the moniker "Fat Head".
- The main plotline for an episode of Honey, I Shrunk The Kids. 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 brain-swapping.
- In Star Trek: Deep Space Nine, this is cited as why Dr. Bashir can lose a portion of his brain and be completely fine. (This was before Bashir was Retconned to be superintelligent.)
- Spoofed in an Italian Real Trailer, Fake Movie parody of Limitless, mercilessly titled Italiano Medio (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 Mythbusters, Tory's brain scans showed him using 15-30% of his brain, depending on what he was doing.
- There are plenty of jokes referring to people without any brain at all working as politicians, lawyers, and the like. An old joke tells of a Brit, a Frenchman, and a German arguing whose medicine is better; the Brit mentions a man whose kidney was removed and he went back to work in three weeks, the Frenchman mentions a man whose lung was removed and he went back to work in two, and the German mentions a man whose brain was removed and he went on to lead the country within a week. Modern variants often replace the three with men from different states, the last one being a Texan talking about George W. Bush.
- Aberrant uses this as part of the Meta Origin 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.
- In Chaos;Head, 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.
- Assassin's Creed has Eagle Sense and Eagle Vision. It lets the user make out if the people surrounding them are friends, enemies or targets. The science behind it all is that humans were created by a race of other beings and then cross-bred when the other race went extinct. Every human has a certain concentration of DNA from those beings and the higher it is the higher this sense is developed. Most people aren´t aware of this ability but it can be awoken through reliving memories of an ancestor. The sense can range from simply seeing people in blue, red, yellow when standing still over being able to walk around while doing it to seeing the paths people went as colored lines.
- This is given as the reason why Fuka, a human Ordinary Middle School Student, can keep up with her demon teammates in Disgaea 4: A Promise Unforgotten. She deluded herself into thinking the afterlife is All Just a Dream, and since it's her dream, she's free to do anything she wants. This allows her brain to unlock her full potential.
- A Cracked article compares this notion to becoming a better writer by using every key on your keyboard in every sentence.
- Parodied in AH Dot Com The Series, 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.
- In To Boldly Flee, it's stated that a critic's brain usage is typically 5%, but Ma-Ti's brain uploading has boosted Spoony's brain usage to 92%.
- Truth in Television to an extent; humans can still function (though not to full capacity, obviously) if parts of their brains are removed. Most notably, the practice of lobotomizing criminals was considered a humane alternative to the death penalty for quite some time. Splitting the corpus callosum (the tissue connecting the two hemispheres of the brain) was a common cure for seizures in the 70s (and is still occasionally done in severe enough cases)note ; the side-effects only occur in very specific, usually engineered scenarios, and are much preferable to the seizures in the first place.
- Removing a damaged hemisphere can even result in a significant improvement in cognitive function... in the other hemisphere, which rewires itself and takes on the tasks once done by the removed half. Whether it improves overall ability is unlikely, given that split-brain patients often act like two people sharing one body, and work at cross-purposes often.
- The basic rule now is that you do not remove any part of the brain unless it's absolutely necessary, because functions are centralized to specific parts, and depending on what is being lost and the patient's age there are distinct upper limits to how much function will be regained. People have permanently lost the concept of color, while prefrontal lobotomies are a good source of Nightmare Fuel...
- One source of the myth itself (of many possible ones) is a series of experiments done on rodents in whch the poor creatures had large parts of their brains burned away but could still run a particular maze. However, all this proves is that memory is distributed in the brain rather than localized; the rodents still lost other functions. Besides, mice aren't men.
- Approximately 90% of cells in the brain are not actually neurons, but glial helper cells that keep the neurons alive and functioning. So only 10% of the cells are used directly; the other 90% are vital to keeping that 10% healthy and alive.
- The famous Phineas Gage had a railroad spike driven through his brain, causing massive damage to his frontal lobes. He recovered and his memories and abilities were intact, but his friends said he was "no longer Gage" - he lost his moral compass and was much more irritable, profane, and dishonest. As the frontal lobes control your personality, this isn't surprising.
- 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!
- Dolphins and other cetaceans have adapted to function actively while 50% of their cerebrum is asleep. This is good, since their breathing is entirely under conscious control, and total loss of consciousness thus equals suffocation.
- Some birds can also have half their brain asleep while the other half keeps watch for danger from one eye.
- Generally speaking, all air-breathing aquatic animals and all land-based prey species that sleep out in the open do this, sleep with only half their brain at a time. Only animals that tend to hide themselves in very well protected locations such as dens or single-family bungalows in the suburbs, can afford to sleep with their entire brain.
- As the savant phenomenon proves, people don't use their brains to their full efficiency. We have potential for far greater mathematical prowess that we normally demonstrate in practice. There have been even a few instances where people have received minor brain damage, and retained most of their faculties quite intact, but gained some savant like skills such as counting dates hundreds of years forward, although they were not as advanced as full savants. Savantism generally has mental disorders attached and what they're talented at is extremely limited. Maybe it's best our brains are a 'jack of all trades' rather than focusing all its time counting cards
- There was a girl who had half her brain gone. The left hemisphere was just not there. So far she seems to be living a fairly normal life with a fairly normal, if quirky, degree of intellect.
- While half of the brain can be removed in a young child and they can still live a fairly normal life due to the other half compensating (due to the symmetrical design and the child's brain being extremely flexible) it's worth adding that an adult who had half their brain removed in adulthood would not be able to function properly.
- May have originated when we only knew the function of (some small percentage) of the brain, and that got misreported as "We only use (some small percentage) of our brain." Areas having to do with other than motor control or sensations are now called "association areas", and they have a role in interpreting, integrating, and acting on sensory input in combination with stored memories. Higher brain functions, in other words. In the same way that your house has only a fraction of its rooms being actively used at any given time, only a fraction - a rather large one - of your brain is active at any given moment - but, as with the house, that doesn't mean the rest isn't useful. The history of this trope is fairly well outlined in the free first chapter of this book. Furthermore, Bill Nye (y'know, the Science Guy) wrote a fairly accessible essay on the subject here.
- It's been shown that the ability to interpret and integrate sensory input takes a large amount of processing power from the brain. Octopuses, with their eight arms, have to give up complete control of their arms just to use them all at once. They still can't form a mental image of whatever it is their arms might be holding.
- TL;DR: We do use all of our brain, it's just that most of it is for things like graphics rather than "consciousness".