A cortical array is a piece of Borg technology implanted upon a humanoid when he or she is assimilated. A cortical array's input leads to a cortical implant, which allows for interface with the mind of the drone; that is to say, the array is used as a storage device and the implant allows for interaction. It is a device which electronically transmits signals to the brain of the assimilant. These electronic signals can contain personalities of the Collective, as well as memories, or perhaps files that have been collected since assimilation, resulting in the possibility of data extraction from a cortical array. When a Borg drone is killed, another drone is designated to remove the killed drone's cortical array to prevent any data extraction, thus preventing tactical exploitation from any enemy. (TNG: "Q Who?", VOY: "Unity", "Night", "Unimatrix Zero, Part I", "Imperfection", Star Trek: First Contact)
- It's slightly interesting to mention that cortical array's have been featured ever since the Borg first appeared, but were first named and elaborted over years past, by the time Voyager encountered the Borg in the Delta Quadrant.