An Evangelion Unit is controlled through a neural-link interface with its pilot, allowing the unit to act as a pseudo-body. The most important of these links is via the A10 Nerve.
Humans have four vertical rows of nerve clusters along the center of the brain stem, and two outer rows are called A nerves. The 10th nerve counting from the bottom is the A10 Nerve, which travels from the brain stem through the hypothalamus and is distributed in the frontal association cortex of the cerebral cortex.
The A10 Nerve is related to such high-level brain functions as memory, recognition, motion, as well as emotions of anxiety, fear, happiness, and pleasure. It is also believed to play a vital role relating to feelings of love between family and lovers.
Based on Neon Genesis Evangelion Platinum: 04 DVD Booklet