Interface Headset

An Interface Headset is a small device worn on an Evangelion pilot's head, which is the primary means by which a pilot controls an Eva Unit. It does this by linking with the cranial nerves of the pilot, thus allowing the pilot to "synchronize" with the Eva and control its movements. Of these nerves, the most important is this "A10 nerve", which is associated with higher order brain functions such as memory, cognizance and the execution of movement, and with emotions such as anxiety, fear, happiness and pleasure. In addition, it is also said to play an important role in affection between parent and child, and between lovers.

Interface Headsets appear to be two small plastic devices placed on top of the head, one on either side. However, the entire headset is actually one object: they are connected by a thin wire tiara of sorts which connects to two larger pieces atop the head. The wire tiara section is always obscured from view because it is nestled under the pilot's hair, making it appear as if the two larger pieces are simply stuck on top of their head.

Asuka Langley Soryu near-constantly wears her Interface Headset, at home and while at school, because she is proud of her status as an Eva pilot and wants the whole world to know that she pilots an Evangelion.

In Volume 1 of the manga adaptation of the series by Yoshiyuki Sadamoto, Sadamoto introduces the bonus materials section at the end of the volume by offering the explanation that:

"On the floor of the midbrain is the ventral tegmental system, that neurobiologists call region A10. Cells soaked in dopamine, certain emotions are processed here: such as the thoughts of two lovers - or a parent and a child. And it is the synchronization of the threads and bundles of A10 that splice pilot and Eva together; to become one entity, to fight. In other words, the power of love drives this weapon of mass destruction."

Notes

• Exactly what Interface Headsets are and how they function is never explicitly elaborated upon on-screen, but is from Gainax-released background material, such as the Red Cross Book.
• Eva pilots are never seen putting on or taking off Interface Headsets during the entire series. The wire tiara which actually connects the two larger pieces and supports them in place on top of the head is also never seen on-screen as a result (it is hidden under their hair), but only in behind-the-scenes production sketches. This has resulted in many fans assuming that the two plastic pieces clearly visible atop the head are somehow just "stuck" on the head, either with adhesive, by being attached like a hairclip, etc. when actually the entire thing is a single headset. As these objects were never formally named on-screen, fans frequently refer to them as "A10 nerve clips", because the description of them in the Red Cross Book says that they interact with the A10 nerve. However, script production notes (released with the Renewal of Evangelion DVDs) clearly and repeatedly refer to the object as an "Interface Headset".