The Doctor's mind

The Doctor's mind was the inner consciousness within the Doctor's brain.

Second Doctor
The Second Doctor confided to Victoria Waterfield that he could only remember his family when he really wanted to, and that the rest of the time they "[slept]" in his mind. (TV: The Tomb of the Cybermen)

Third Doctor
During the Time Paradox Incident, the Daleks used a Mind Analysis Machine to forcibly ascertain the identity of the Third Doctor, projecting the familiar images of the First and Second Doctors on their screen. (PROSE: Doctor Who and the Day of the Daleks, TV: Day of the Daleks)

The Third Doctor once saw images of inside his mind during a nightmare. (TV: The Time Monster)

Fourth Doctor
The Fourth Doctor challenged Morbius to a mindbending contest on the planet Karn, eager to prove the latter's mental instability following his surgical revival. Although Morbius's face appeared first, the screen began showing the Doctor's face, followed by his first three incarnations, then eight of the Doctor's earlier lives before the device burnt out. (TV: The Brain of Morbius) Both were badly hurt by the fight, with static electricity fusing the circuits in Morbius's brain case, reducing him to a mindless monster. (PROSE: Doctor Who and the Brain of Morbius) The Doctor was left dying, only being restored when the Sisterhood of Karn had him drink the Elixir of Life. (TV: The Brain of Morbius)

In a dream, the Doctor encountered his previous incarnations in a heavenly garden, which made him aware that his own regeneration was on the horizon. (PROSE: Into the Silent Land)

Fifth Doctor
During his regeneration, the Fifth Doctor was trapped in a dreamscape by, exploiting a residual link between their minds from their connections with Kamelion, in an attempt to stop the process. The Doctor subconciously reached out telepathically to Nyssa who helped him break free and complete the regeneration. (AUDIO: Winter)

Seventh Doctor
During the Seventh Doctor's battle with the Timewyrm, Ace entered the Doctor's mind, encountering various past Doctors in various guises, including the First, Third and Fourth Doctors. She discovered the Fifth Doctor had become symbolic of the Doctor's conscience and freed him from the confinement the current Doctor's persona had put him in so he could what he believed was necessary to stop the Timewyrm. (PROSE: Timewyrm: Revelation)

Bernice Summerfield entered the Doctor's mind after the Seventh Doctor was possessed by the Scourge. She tried to help him resist their despairing influence and caught glimpses of his past selves and possible future self. (AUDIO: The Shadow of the Scourge)

Fearing his potential to become the Valeyard, the Seventh Doctor buried the memory of his predecessor deep within his mind. (PROSE: Head Games) After being buried alive, the Seventh Doctor came to recognise no-one deserved to be trapped this way and released him. (PROSE: The Room With No Doors)

Eighth Doctor
When the Eighth Doctor was possessed by Zagreus and stabbed by Charley Pollard, he met the mental manifestations of his fifth, sixth and seventh incarnations in his mind when he nearly allowed himself to die, subsequently rallying himself with their aid to restore himself and retake control of the anti-time energies. (AUDIO: Zagreus)

The Eighth Doctor tricked the Kro'ka into entering his mind, where he was able to briefly hold him prisoner and interrogate him for information on the whereabouts of his TARDIS. (AUDIO: Caerdroia)

To preserve the Time Lords from the iminent destruction of Gallifrey he'd caused to stop Faction Paradox, the Eighth Doctor and Compassion copied the entire Matrix, containing all the Time Lords' dying minds, into his mind. This suppressed his own memories, rendering him amnesiac. (PROSE: The Gallifrey Chronicles)

Whilst exploring his own mind, the amnesiac Eighth Doctor found the Seventh Doctor sleeping in a garden of roses. When the Eighth Doctor tried to dive deeper into his memories, the Seventh Doctor awoke to stop him, and forced him to leave his mind. (PROSE: The City of the Dead) Later whilst meditating the amnesiac Eighth Doctor met the Seventh Doctor again, who asked him how Ace's memory of her trip to Paradise Towers could be relevant and told him that there were 153,841 blossoms in the garden, and that the trick to counting them is to subtract five from the end; both clues to help him deduce the Time Lord minds were within his head. After learning the truth about his amnesia, the Doctor planned to find a way to restore the Time Lords. (PROSE: The Gallifrey Chronicles)

War Doctor
Under the influence of an experimental Time Lord weapon during the Time War, the War Doctor was forced into a dreamscape where he was still the Doctor, travelling with a companion he later theorised was drawn from traits of several of his old friends. He eventually forced himself awake. (AUDIO: The Keeper of Light)

Tenth Doctor
Whilst possessed by Lady Cassandra, the Tenth Doctor blocked her from seeing any information in his mind such as how to operate the sonic screwdriver. (TV: New Earth)

When the Doctor connected with Jeanne-Antoinette Poisson's mind to try to deduce why Clockwork Droids were seeking her brain, she was able to use the connection in reverse to see into his mind and glimpse his childhood memories, to his surprise. (TV: The Girl in the Fireplace)

Donna Noble gained the Tenth Doctor's mind in the meta crisis caused by touching his severed hand while it was infused with regeneration energy from a recent regeneration. However, given she was human, the Tenth Doctor had to remove all memory of himself from her soon after to ensure her mind did not burn from trying to possess a Time Lord consciousness. (TV: Journey's End)

The Tenth Doctor once encountered his next incarnation in a dream, assuring him that they would both be fine. (COMIC: To Sleep, Perchance to Scream)

Eleventh Doctor
The Eleventh Doctor rapidly connected his mind with Craig Owens' to speedily share information, although the process resulted in a mild headache. (TV: The Lodger)

Mr Clever attempted to take over the Eleventh Doctor's mind when trying to convert him into a Cyber-Planner. The mind was subsequently split into two halves; 49.881% in the Doctor's control and 49.881% under Mr Clever's influence. The two sides differentiated, with Mr Clever's half coloured silver and blue with circuitry scattered around, while the Doctor's was orange with Gallifreyan symbols covering it. (TV: Nightmare in Silver)

Twelfth Doctor
During the Good Dalek Incident, the Twelfth Doctor made telepathic contact with the damaged Dalek known as Rusty, hoping to remind him of the beauty of the universe. Rusty, however, was inspired to kill the Daleks by seeing the hatred for them in the Doctor's mind. (TV: Into the Dalek)

The Doctor could willingly enter his mind to quickly deduce problems when under extreme duress. While there, his mind took the image of his TARDIS while he worked out solutions. Given how quickly his mind processed information, what seemed like minutes to him was mere seconds outside his mind. (TV: Heaven Sent)

Thirteenth Doctor
The Thirteenth Doctor and telepathically linked their minds to talk in 1943 Paris. (TV: Spyfall) The connection lingered afterwards, with them using it at one point to telepathically talk over their past until he broke it off. (PROSE: The Doctor vs the Master)

The Doctor used telepathic contact to project the image of the ruined Gallifrey of her time from her mind to that of Gat, a Gallifreyan from her past. (TV: Fugitive of the Judoon)

During her encounter with the Cybermen, the Master broadcast the story of Brendan from the Matrix into the Doctor's mind. (TV: The Timeless Children)

Swarm retained a link to the Doctor's mind from their battles in lives erased from her memory by the Division. He reactivated it to show the Thirteenth Doctor his escape and later taunted her via it as the Flux approached her TARDIS. (TV: The Halloween Apocalypse)

After being forced to regenerate by the Master, the Thirteenth Doctor passed into her mind but was halted at the Edge of Existence by manifestations of her past selves, calling themselves the Guardians of the Edge, to stop her going past the point of no return. This enabled Yaz and Vinder to restore her via degeneration. (TV: The Power of the Doctor)

Behind the scenes

 * J. K. Woodward, who worked on the Star Trek crossover Assimilation², released a piece depicting Spock gleaning the image of a jelly baby in a with the Fourth Doctor.
 * The use of the Mind Analysis Machine in Day of the Daleks was parodied in an instalment of Doctor Whoah!, where the Doctor is flustered as his mind wonders toward a romanticised image of the Brigadier in his underpants, and he tries to convince the Daleks that it is nothing more than "a brilliant fiction" he concocted to distract them.