Neuro Vault

You have vital data so dangerous that there must be absolutely no chance of it falling into the wrong hands. Where do you hide that data?

You bury it in someone's mind.

Burying data in a person's subconscious as a result of a post-hypnotic suggestion is a common MacGuffin in sci-fi and spy thrillers. Very often, the person will have no idea of what he's carrying around, usually by design. Also expect that the person will be someone you'd least suspect. Could be a child or a fool; it could even be the hero who was unaware that he was carrying what he sought all along. Frequently used to create the Manchurian Agent.

Compare the various amnesia tropes, such as Criminal Amnesiac and Easy Amnesia. See also Neural Implanting, another method this can be done.

May result in My Skull Runneth Over. This may be the result of a time delayed Exposition Beam. If you're doing it to yourself, it's usually part of a Memory Gambit.

Examples of Neuro Vault include:

Anime and Manga

Dolls in Darker than Black can be used for this.
Index Librorum Prohibitorum from A Certain Magical Index has 103,000 grimoires stored in her brain.
Lain herself in Serial Experiments Lain.
The Whispered in Full Metal Panic!. Played With in that they might have access to data stored in somebody else's brain.

Fan Works

In the Haruhi Suzumiya fanfic Kyon: Big Damn Hero Mikuru keeps a collection of recorded memories for reference when she has to return to her own time.

Films

Johnny Mnemonic
The Manchurian Candidate
Flight of the Navigator was about a little boy that had all sorts of star charts from aliens temporarily stored in his brain, and was later picked up for retrieval when the alien robot accidentally lost its own copies.
Used as the hook to bring Agent K back from being neuralyzed in Men in Black II.
In Star Trek III the Search For Spock we discover that at the end of the previous movie, Spock placed his soul in Doctor McCoy just before his Heroic Sacrifice.
Mystery Science Theater 3000 alum Operation Double 007 spent its first half chasing after a woman who had been given sensitive information by a deceased operative. The trick was, it had been given to her while she was under a certain kind of deep hypnosis, and could only be retrieved if she was put back under in the exact same way.
Sebastian Rook does this on himself in Cypher.
The entire mission of the Inception is to do exactly this, though instead of information, the goal is to implant an idea. As well, Browning suggests that Fischer Sr. may have done this to his son in the first dream layer.

Literature

In the book version of The Hitchhiker's Guide to the Galaxy, Zaphod buries the location of the man who rules the universe within his brains.
- Because in this universe Earth is a supercomputer designed to find the Ultimate Question of Life, the Universe, and Everything, all Earthlings have the Question imprinted in their subconscious.
  - Humans apparently aren't Earthlings.
In Abarat by Clive Barker, an important key is hidden in Candy's mind, despite its apparently being a physical object.
From Midnight at the Well of Souls: Vardia Diplo 1261 is, for the most part, a human casette reel—a Neuro Vault with legs. A message is encoded in her head, to be shuttled to another planet's embassy, where the vault is unlocked, and she's basically written over with the base "Diplo program". Also, I think the Well World series could use a little more love?
In Man Walks Into A Room, a group of scientists attempt to implant a memory from one person into the protagonist's brain. The memory itself, to the scientists, is only important in that it's a strong, easily distinguished, distinctive memory, not in terms of its content: a nuclear weapons test occurring too close to a group of soldiers.
Haruki Murakami's Hard-Boiled Wonderland and the End of the World is about a man whose subconscious is used to store classified data in a cyberpunk future.
Forgotten Realms has its share of memory transfers, but specifically in Return af the Archwizards the wizard spy dropped lots of reconnaissance data (for all we know, it could be centuries worth of examining Sealed Evil in a Can while hiding inside the same can) to another guy, because he was dying and it was the only way to save priceless knowledge. Carrier used this memory only as provoked "I just feel it must be so" insights, even after he understood what's going on (which still made him so valuable that dead wizard's boss could neither let him go nor kill him, nor even use outright mind control).
In The Search for Snout, the third book in Bruce Coville's alien series, it's revealed near the end that the main character has a secret piece of data in his brain that will allow the villain to literally destroy time.
In Robert A. Heinlein's Citizen of the Galaxy, Obi Wan Baslim hypnotizes his foster son Thorby into memorizing a coded final report to the Space Police, as well as a message to a ship's captain to help Thorby escape off-planet.
This is pretty much the entire premise of One of Us by Michael Marshall Smith. The main character makes his living storing memories that others want to get rid of temporarily—for instance, a businessman about to screw over his partner hands over a memory of a moral lesson from his father. (Permanently destroying a memory screws up The Force.) Unfortunately for him, someone figures out that this can work as Laser-Guided Amnesia for the giver, and that the Big Bad only wants to kill anyone who remembers a particular secret.
In Piers Anthony's Macroscope, Brad Carpenter hides information about Schon inside Afra Summerfield's mind.
In Sword of Truth, Richard's adoptive father had him memorise a book, destroying it after he was satisfied that Richard could recite it verbatim. The first book of the series revolves around the Big Bad's attempts to extract this information from him.
- There is also another example, when Richard prevents himself from going fully mad due to Cold-Blooded Torture by locking away the core of his personality.
The distrans of the Dune universe is used to encode messages in the voices of bats and birds. It can be used on humans, but it is frowned upon.
The Amnesia Arc in the Eighth Doctor Adventures (and the EDA series itself) ends with the revelation that the Doctor's amnesia was caused by downloading the entire Time Lord matrix into his mind, thereby enabling Gallifrey to be restored from backup at a future date.

Live Action TV

Blakes Seven. The location of Star One (the Master Computer that runs the Terran Federation) is buried in the mind of the King's Fool on a primitive planet.
The whole premise of Chuck - the Intersect is an incredibly comprehensive espionage database so important it can't be trusted to a computer (or, apparently, spread among many computers) so it's uploaded to the mind of a master-spy. Unless it should accidentally be uploaded into that master-spy's college roommate...
Dark Angel
Firefly. In this case, it turns out to have been entirely accidental, and those whom the information concerns want to keep it under wraps.
Played for three years and The Movie of incredible dramatic effect in Farscape. John Crichton has the secret to wormhole technology buried in his mind by Sufficiently Advanced Aliens. The idea is that John doesn't know he has this dangerous information (which could be used to alter reality or create a Doomsday Device) but his subconscious knowledge will give him an 'instinct' for wormholes that will help him get back to Earth. Unfortunately this fact is uncovered by the Big Bad Scorpius, who spends the rest of the series trying to rip the knowledge from Crichton's head.
O'Neill frequently gets his head packed full of deadly amounts of Lost Wisdom from The Ancients, barely surviving long enough to get it extracted by the Asgard on Stargate SG-1.
Donna Noble on Doctor Who is a variation on this trope. She has Time Lord knowledge embedded in her brain, and for her own well-being she had to lose all her memories of the time spent with the Doctor. If she were ever allowed to remember him or her adventures all over the universe, it would destroy her.
In Harper 2.0 of Andromeda Harper gets the largest library in the universe downloaded into his brain. This slowly begins to burn up his brain until he gets rid of it. It's used for a Continuity Nod later when trying to remember where he hid some of the data.
In Fringe, William Bell removed pieces of Walter's brain and put them into other people's brains in order to prevent information about how to get to the other universe from falling into the wrong hands.

Theater

In The Thirty-Nine Steps, the top secret information the bad guys are trying to smuggle out of the country is hidden in the mind of the "Memory Man", a showman who has the ability to take in such information.

Video Games

It's commonly agreed that the player character in Marathon Infinity smuggles Durandal across timelines within his own brain toward the end of the game.
Similarly, Jake in the SNES Shadowrun game has some sensitive files in his head computer, which starts off locked until an attempt to repair it sets off a Cortex Bomb. This is, of course, perfectly normal within the confines of the Tabletop Game.
- It's implied that Jake did not undergo the procedure willingly, as a character met earlier on notes that the head computer and datajack are new additions. Jake himself has complete amnesia, though.
Xenosaga Episode III uses this in an interesting way. The Godwin sisters hold the two parts of the unlock code which opens the Zohar Emulator storage. Both are aware of this, and didn't require any messy mind tricks -- their minds already had uplink ports from their previous "jobs" before the Durandal.
- The Realian MOMO has the politically and functionally dangerous Y-Data stored in her head.
- Xenosaga does this a lot, actually; Canaan, another Realian, likewise has part of the Y-Data dropped into his head; he's blocked from accessing it, which makes him very grumpy. He spends the better part of fifteen years trying to get it out and failing.
Asimov, the hero of Mr. Robot, saves his friends from being permanently scrapped by downloading their brainmaps into his system. Conveniently enough, this is also how you add members to your party for hacking missions.
A variant in Knights of the Old Republic. Your character was getting Force visions and flashbacks of an allegedly-dead Sith Lord.Through those visions, you and Bastila were trying to find the Sith's hidden superweapon/base/Death Star prototype. Turns out that said Sith Lord wasn't dead, after all.

Web Comics

The titular carbosilicate amorph pulled one of these in Schlock Mercenary.
Order of the Stick: Redcloak was convinced the paladins of the Sapphire Guard had pulled this, though he appears to have been wrong.
- He knew there was no Neuro Vault. Torturing O'Chul for information was Redcloak's excuse for staying in Azure City.
  - Hell, Redcloak himself has his own Neuro Vault with the divine part of the ritual to 'control', really 'transfer control' of the Gate's position to his deity, imparted to him by the Red Mantle. It qualifies as it was never commited to paper. It's not that far of a stretch for him to expect opposing forces to use the same kind of trick.
Homestuck: The genetic code for the creation of a first guardian is locked away within the minds of one or more players, who end up writing it on their walls and in a book. It winds up being unlocked by some sort of important event. In the kid's session, Rose wrote it in one of her journals, while in the troll's session it was unlocked via the infamous Team Charge debacle, and authored by Tavros, Aradia, Vriska, Terezi, and a doomed timeline Gamzee, who wrote it in their FLARPing manuals and Karkat's ~ATH book.

Western Animation

Code Lyoko: Franz Hopper hid the "keys to Lyoko" that XANA would need to escape inside himself and Aelita.
G.I. Joe, "There's No Place Like Springfield": Plans for a deadly super-weapon are implanted into Shipwreck's head, and can only be retrieved if a certain code word is spoken to him. Cobra conducts an elaborate ruse to try and figure it out.
- And even then, the code turns out to be a code phrase. ("Frogs In Wintertime")
In Beast Wars, Blackarachnia purposely downloads the data on the golden disks, which were stolen by Dinobot, and which contain the entry code to the Ark into her own brain and destroys the computer containing the original copy so that Megatron can't use it.