Direct Neural Link

Roughly 15 years ago, prosthesis and augmentation technology appeared to have plateaued. While augmentations could be linked directly to the user's existing nervous system, the degree of control still wasn't matching what ordinary individuals could accomplish naturally. As it turned out, the necessary breakthrough was found by avoiding the issue entirely.
The Direct Neural Link skips the existing nervous system entirely, providing a direct link between the augmentation and the subject's brain matter. This allows the subject to control the augmentation seamlessly, as if it were truly a part of their own flesh.

Accessibility

Within the cities, neural links are generally used for medical purposes and access to them is essentially unrestricted. Some urban areas will permit use of neural links for additional augmentations, though they frequently need to be approved as necessary for an individual's duties within the community. In addition, even when available, the surgery necessary to install a DNL may be prohibitively expensive - an individual becoming indebted to the corporation in exchange for the procedure is not an uncommon occurrence.
Outside the walls, accessibility is primarily limited by availability of the neural links themselves. As most technology is manufactured within the cities and their controlled domains, the technology is only available through smuggling and black markets. When available, however, direct neural links are offered for much wider purposes Outside. The Outsiders frequently view augmentations - and the neural links associated with them - to be elective body modification as well as medical prostheses.

Utility

As its basic purpose is to enable direct limb interface, DNL technology is used primarily for medical prostheses. Some more permissive cities also allow DNL use for additional augmentation, such as the installation of manipulators with enhanced dexterity. In contrast, Outsiders use neural interfacing technology for a much broader array of purposes, such as additional arms, altered legs, or even wings or tails.
Some enterprising individuals, both within the cities and Outside, have suggested that neural interfacing could also be used to allow ordinary individuals to control larger machinery - possibly even autonomous machinery - as if it were part of their own body, but those possibilities are still in the early stages of research.