Vinculum

A vinculum was a processing device at the heart of every Borg vessel which interconnected the minds of all the drones, purging individual thoughts and disseminating information relevant to the Collective. The vinculum was equipped with many safeguards to prevent its deactivation, and was capable of adapting to attack. It could also repair drones seperated from the collective by bombarding them with personalities

In 2375, Species 6339, a Delta Quadrant race which had been almost completely assimilated by the Borg, intentionally infected a Borg cube with a synthetic pathogen designed to attack the vinculum's programming as it would living cells. The drones aboard the cube subsequently began to experience an inability to suppress the various neural patterns of the individuals assimilated by the Borg, causing chaos to spread throughout the ship. Within three days of infection, the cube was destroyed. The vinculum, which survived the destruction of the ship, then established a connection with Seven of Nine's cortical implant via interlink frequency, causing her to develop the same symptoms as the crew of the cube. Seven began to experience extreme difficulty in controlling the identities which were surfacing, essentially developing the Borg equivalent of multiple personality disorder. The crew of the USS Voyager subsequently attempted to deactivate the vinculum by targeting a dampening field at its transneural matrix, but were unsuccessful in their attempts as the vinculum began adapting by rerouting its internal circuitry. Despite an attempt by Species 6339 to forcibly retrieve the vinculum from Voyager, Lieutenant Torres was successfully able to remodulate the dampening field to compensate for the adaptation. Captain Janeway then ordered the vinculum beamed into space, where Species 6339 retrieved it and withdrew from attacking Voyager.