These are cybernetic implants that alter the way a person perceives or thinks. They are tiny - usually pill-sized or smaller. They can be safely implanted or removed by robotic microsurgeons in a few hours. Removal is slightly trickier, as activation of an implant involves weaving a network of nanocommunicators and nano-optical threads through the brain.

About half a billion people have brain implants, mostly in Fifth Wave cultures. Laws usually require minors to have parental permission before getting brain implants.

A radio communicator buried in the head. It can send and receive subvocalizations or, if the user also has a virtual interface, digital data.

This is the commonest brain implant, with functionality akin to a standard wearable virtual interface, providing personal computing and augmented reality. It translates brain activity into digital signals that can be transmitted via a microcommunicator, allowing mental control of a computer or other electronic device with similar precision to someone using a mouse, keyboard, or voice input device. While it permits commands to be entered 'with the speed of thought', that's about the same speed as a good typist. Devices do not need exotic equipment to be run through a neural interface - any microcommunicator-equipped computer or dedicated computer is usable.

As with other virtual interfaces, it normally houses an infomorph. Most people prefer to share their heads with nonsapient or at most, low-sapient AIs, but it's quite possible for a high-end implant to run a sapient AI or even a mind emulation of another person. In some circles, it's common to have an implant hosting a shadow of a current or lost love, close friend, parent, mentor, or guru. The Pope and Dalai Lama both reacted with horror to suggestions they be brainscanned so that every one of the faithful could have their own spiritual advisor, but other spiritual figures have been less conservative, resulting in so-called xox cults.

'Upslink' implants translate the user's sensory experiences, including subvocalized thought, into compressed digital data ('sensory link experience'). This can be transmitted through microcommunicators or implant communicators in real time to someone with a sensory downlink, or recorded on digital media. An upslink could also store data in the computer contained within a virtual interface. Upslinks may be built so slink output is controlled by the user (active upslink) or by someone else (remote upslink); the latter are most often used to monitor convicts or study animal behavior.

'Downslink' implants allow someone to experience slink input, either prerecorded or live. Two people who both possess upslink and downslink implants can experience a form of telepathy; a downslinker can read the surface thoughts of an upslinker he is in contact with. Downslinks also allow supervisors to 'snoop' on what subordinates with remote upslinks are thinking and doing, although privacy laws usually ban this, at least with humans.

It's possible for a single upslink feed to be retransmitted to multiple, even millions of downslinkers. Such feeds also offer the ultimate form of virtual reality entertainment, although mainstream shows such as news are usually delayed by 1 or 2 seconds, passing through a downslink editor who makes a snap decision to delete anything unpleasant or embarrassing.

Slink recordings can be edited, and such 'slinky' media, usually accessed via the Web, is big business, especially for things like porn, cooking, sports, or real or scripted dramas where you 'live the experience'.

Downslink implants are very common (with over 100 million currently in use); Fifth Wave teens beg their parents for them. Upslinks are usually limited to specific occupations.

Implant interfaces, implant communicators, upslinks and downslinks are all socially acceptable, limited only by their expense and the reluctance of healthy people to undergo brain surgery. More exotic implants are used for psychiatry and mind control. The most sophisticated are puppet implants, which allow one mind to control another's body. A puppet implant can allow remote control of a person, but this is difficult due to bandwidth limits. Puppet implants are more effective if the controlling mind is right there - a puppeteer can be an AI integrated into a virtual interface implant.

Implants are capable of synergistic effects. For example, a person might voluntarily accept a puppet implant that is accessible to multiple AIs (or shadows) running on a virtual interface computer implant in his brain. If the AIs are under the host's control, this allows him to effectively switch his body between different 'personalities' optimized for specific situations.