In Star Trek: First Contact, what technology does the Borg use to alter Captain Picard's body?

In Star Trek: First Contact, the Borg use cybernetic implants to alter Captain Picard's body.

Picard was assimilated by the Borg before the film's events and became Locutus of Borg. Although Starfleet later recovered him, traces of Borg cybernetics remain in his body. In First Contact, Picard reveals that he can sense the Borg and their communications because of those implants and his past connection to the Collective.

The film shows that assimilation is more than a change of allegiance. Borg victims receive mechanical and electronic components that link them to the Collective and enhance physical functions. The implants are part of the wider Borg process of converting individuals into drones.

These implants are not the same as the microscopic assimilation devices used to begin assimilation. Nor are they ordinary medical prostheses. Their defining feature is integration with Borg systems and the Collective's network, which makes Picard's experience different from a conventional injury or replacement limb.