They, the Doctor-TARDIS, lend him some control. They alter the synapses of his mind, using the non-artron (which, though they do not know this, will hurt him later, but that physical hurt will pass) to knit those sensory parts of his brain into something like their original configuration.

This will make the drums quieter, less acutely-felt, for a time. But it is only a temporary measure; they have hurt his brain, not healed it, and his Gallifreyan biology will cure the "damage" quickly enough, returning his senses to the full potential they developed under duress. The duress of a year that never happened, but which lives on in him, in its effects on him, regardless.

When the alterations are complete, they withdraw from his mind, back into themselves. And then they find that they remember the trick to redividing, because they have done all they need to do, for now, as a whole and can go back to being almost-separate.

So she recedes to the back of his mind, the greater part of her flowing back into herself, and he sleeps, because he cannot remember this, cannot hold all that has happened, without her to help him.

The Doctor in black loses consciousness, hands slipping down from his other's temples, slumping forward against him.

The room glitters with non-artron.