How Amon Removed Bending (It’s a real Chinese technique that many believe in)
When placing his thumb on the center of the forehead, Amon was aiming for the hundred-meetings acupoint (shown above, circled in red). This is a central gateway and nexus for chi. Bending relies on chi flowing through the bender’s body. The idea of this technique is to send chi through the acupoints the wrong way and damage the veins and energy channels. This could be forced with bloodbending. The hundred-meetings acupoint is connected to all the important points through the chi paths, so it is the best spot to cause massive damage.
It is said that a divine doctor can cure internal injuries and restore one’s martial arts power. The injured person could also practice a special, high level skill to regain his inner power. Bryke obviously made the Avatar the parallel to this, as Korra was able to look inside herself to restore her own bending, and she had the ability to restore other’s bending as well.
Also, notice the placement of the red dot on his mask below: