From Post-Self

An Exocortex is a cybernetic implant taking the form of a column running along the base of the spine. Phys-side, it is used as part of the immersive simulation technology that makes up the net. Exocortices control much of the technology that consists of interfacing with a Phys-Side net sim.[1]

  1. the Post-Self Universe, Immersive tech.