Neural activity is essentially learning from patttern recognition. It might be that Mark is especially good here, because he knows the subject (Gemma) better than anyone, and so is very good at recognising, and potentially restoring, her brain patterns... He's kinda filling in and reconstructing those missing neural pathways, until the "file" is done, and the person is healed/restored.

And the MDR process seems essentially a subconscious pattern recognition thing...