Cortical node
A cortical node was a small, circular medical device. Usually, two of them were attached to either side of a person's forehead.

In 2153, two cortical nodes were used for Starfleet Commander Charles Tucker III, while he was comatose. They were metallic with a red light in the center. ()

A Borg cortical node was an implant that sat in a socket above the right eyebrow, as a part of a Borg drone's cortical array. () It was the single most important component a Borg drone possessed, as it served in controlling all of the drone's other cybernetic implants. If the cortical node malfunctioned, the implants would fail and be rejected, killing the drone. Its technology was too advanced to attempt any form of repair and replacement nodes were incapable of being replicated; in the Borg Collective, if a drone's cortical node malfunctioned, the node was replaced entirely. If a drone had been dead for more than an unspecified period, its cortical node became inactive and therefore could not be used to replace a malfunctioning node. ()

Built into every cortical node was a fail-safe mechanism designed to shut down the higher brain functions when the drone achieved a certain level of emotional stimulation, in order to deactivate drones who started to regain their emotions. This was to prevent the drone's mind from regaining a sense of individuality, breaking the Collective's control over it. () Individuals rescued from the Borg Collective still required their cortical nodes in order to keep any remaining Borg implants not removed functioning despite no longer being part of the Collective; it was possible in some cases to bypass this need using genetic resequencing, although this procedure was painful and only effective on those with a much lesser dependency on their implants such as adolescents. ()

de:Kortikalknoten
Medical equipment
Borg components