From the Doctor Who episode Journey's End transcript:

DONNA: I thought we could try the planet Felspoon. Just because. What a good name, Felspoon. Apparently, it's got mountains that sway in the breeze. Mountains that move. Can you imagine?
DOCTOR: And how do you know that?
DONNA: Because it's in your head. And if it's in your head, it's in mine.
DOCTOR: And how does that feel?
DONNA: Brilliant! Fantastic! Molto bene! Great big universe, packed into my brain. You know you could fix that chameleon circuit if you just tried hotbinding the fragment links and superseding the binary, binary, binary, binary, binary, binary, binary, binary, binary, binary, binary, binary, binary, binary. (gasp) I'm fine. Nah, never mind Felspoon. You know who I'd like to meet? Charlie Chaplin. I bet he's great, Charlie Chaplin. Shall we do that? Shall we go and see Charlie Chaplin? Shall we? Charlie Chaplin? Charlie Chester. Charlie Brown. No, he's fiction. Friction, fiction, fixing, mixing, Rickston, Brixton.
(This time it hurts.)
DONNA: Oh, my God.
DOCTOR: Do you know what's happening?
DONNA: Yeah.
DOCTOR: There's never been a human Time Lord metacrisis before now. And you know why.
DONNA: Because there can't be. I want to stay.
DOCTOR: Look at me. Donna, look at me.
DONNA: I was going to be with you forever.
DOCTOR: I know.
DONNA: The rest of my life, travelling in the Tardis. The Doctor Donna. No. Oh my god. I can't go back. Don't make me go back. Doctor, please, please don't make me go back.
DOCTOR: Donna. Oh, Donna Noble. I am so sorry. But we had the best of times.
DOCTOR: The best. Goodbye.
DONNA: No, no, no. Please. Please. No. No.
(The Doctor mind melds with Donna and takes her memories away.)
(Donna passes out.)
DOCTOR: She took my mind into her own head. But that's a Time Lord consciousness. All that knowledge, it was killing her.
WILF: But she'll get better now?
DOCTOR: I had to wipe her mind completely. Every trace of me, or the Tardis, anything we did together, anywhere we went, had to go.
WILF: All those wonderful things she did.
DOCTOR: I know. But that version of Donna is dead. Because if she remembers, just for a second, she'll burn up. You can never tell her. You can't mention me or any of it for the rest of her life.

So the Doctor-Donna couldn’t deal with having the Doctor’s mind in her brain.

But the human Doctor born out of meta-crisis earlier in the same episode never showed any kind of insanity till the end, and The Doctor also wasn't worried about that. He was talking about spending his life with Rose.

The meta-crisis Doctor had human brain, and he possessed a Time Lord consciousness with the entire knowledge of The Doctor.

Why wasn't he affected in the same, or any, way?

My mistake that I didn't realize meta-crisis Doctor was a hybrid, but Doctor-Donna was also a hybrid. In the episode The End of Time, The Master transformed all humans into himself, but Doctor-Donna wasn't affected.

Update 2:
To prove that Donna was really a hybrid, here's quote from Journey's End:

DALEKS: Exterminate. Exterminate. Exterminate.
(Donna works more controls on the panel.)
DALEK: Weapons non-functional.
DONNA: Phwor. Macrotransmission of a K-filter wavelength blocking Dalek weaponry in a self-replicating energy blindfold matrix.
DOCTOR: How did you work that out? You're
NEW DOCTOR: Time Lord. Part Time Lord.
DONNA: Part human. Oh, yes. That was a two-way biological metacrisis. Half Doctor, half Donna.
DOCTOR: The Doctor Donna. Just like the Ood said, remember? They saw it coming. The Doctor Donna.

  • The doctor added a defense mechanism to Donna. He says so in end of time part 2 – user16696 Jan 30 '15 at 20:24
  • @cde Don't take words literally. By defense mechanism, he meant meta-crisis. – Wakanda Forever Jan 30 '15 at 21:01
  • 2
    It was a two-way metacrisis, as Donna stated, but that doesn't mean 50% transfer. I think it's more likely that Crisis-Ten was moved a small way towards human (let's say 20%), which made him lonesome-hearted and incapable of regenerating. Likewise, Donna was moved 20% towards Timelord, which was probably enough to help her in The End of Time, but not enough to allow her to safely store all the information that she'd obtained from the Doctor. I don't have any quotes to back this up, unfortunately; it's just my interpretation. I won't put it as an answer unless you think it fits. – Liesmith Jan 30 '15 at 22:58
  • @Liesmith I think, half means 50%. – Wakanda Forever Jan 31 '15 at 3:03
  • 1
    @SS Don't take words literally. By half, he means partially. – Liesmith Jan 31 '15 at 7:19

DONNA: What, like you're human?
NEW DOCTOR: Oh, that's disgusting.
DONNA: Stop it.
NEW DOCTOR: No, wait. I'm part Time Lord, part human. Well, isn't that wizard? 

The meta crisis doctor is a hybrid, a unique one if we take him at his word.

Donna only received the doctors entire memories and knowledge, no other changes. That's what makes the two different, and why Donna started having seizures while 10.2 didn't.

There is more expository bits in the rest of the same episode transcript.

  • But, Doctor-Donna was also part Time Lord as displayed in End of Time.. – Wakanda Forever Jan 30 '15 at 19:27
  • @SS that's a defense mechanism the doctor put in place. – user16696 Jan 30 '15 at 20:25
  • Back this up with quotes if you think so. – Wakanda Forever Jan 30 '15 at 21:01
  • @SS DOCTOR: That's better. Hello. But really, did you think I'd leave my best friend without a defence mechanism? – user16696 Jan 30 '15 at 21:04
  • 1
    Lack of information about Donna proves nothing. I am quoting Donna again: That was a two-way biological metacrisis. – Wakanda Forever Jan 30 '15 at 21:31

Genetically, the meta-crisis Doctor is still half Time-Lord. He had many human characteristics (one heart, not regenerations) but he was not a human being like Donna was:

Soon after his "birth", he says:

NEW DOCTOR: No, wait. I'm part Time Lord, part human.

Later, in Pete's dimension:

NEW DOCTOR: I'm part human. Specifically, the aging part. I'll grow old and never regenerate

Though he has some human traits, he is not human; he is a Time-Lord/human hybrid. He was formed from Ten's DNA mixed in with bits of Donna's DNA, giving him part of her personality, but that didn't make him human.

Thus, it's not really valid to compare him to Donna and expect the two of them to experience the same effects; obviously, whatever makes Gallifreyan brains different from human brains to let them contain all that knowledge is present in the meta-crisis Doctor's brain.

  • Genetically, the meta-crisis Doctor is still half Time-Lord. ~> Citation? Tell me one Gallifreyan characteristic he possessed. – Wakanda Forever Jan 30 '15 at 11:35
  • Also, comparing River Song would be nuts. She didn't have the entire knowledge of The Doctor. – Wakanda Forever Jan 30 '15 at 11:36
  • Characteristics aren't important. Time Lords and humans have no genetic relation, they just happen to look (almost) the same. He may look entirely human but his genetics may be entirely different. – George T Jan 30 '15 at 12:00
  • @SS the citations are the times he said so himself, which I've added in. – KutuluMike Jan 30 '15 at 15:53
  • But, Doctor-Donna was also part Time Lord as displayed in End of Time.. – Wakanda Forever Jan 30 '15 at 19:27

In the Trenzalore episode the Doctor clearly states that a body is something a time lord possesses, and clearly not identical to the timelord itself.

Clara: What's that?
The Doctor: What were you expecting, a body?Bodies are boring. I've had loads of them. That's not what my tomb is for.

I think the metacrysis Doctor is a hybrid of the body the Doctor possesses at that time and Donna Noble. Of course that body contains as much of the Doctor as possible, but not him. Not fully.

Also Donna Noble after the metacrysis is a hybrid of Donna Noble and the Doctor (and not only his body) so I guess she is way more unstable than the other being.

  • Most of the answer is somewhat agreeable, but that finally part is completely wrong. We see 10-2 several times after his creation. The last time we see him is on the beach with Rose. – Omegacron Jan 30 '15 at 15:18
  • I assume you are right and edit my answer accordingly. – mg30rg Jan 30 '15 at 15:25
  • That quote is out of context... he was talking about a time travelers remains. If you want a better quote, the doctors daughter points out the difference between Gallifreyan and time lord. A shared code, knowledge, not just two hearts. – user16696 Jan 30 '15 at 18:13

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