The chronometric node measures the passage of time.
The Cortical Node is part of the Cortical Array. It is a device located above the right eye brow which controls controls and regulates all of the other drone's implants. The device also possessed an additional built-in fail-safe mechanism to prevent a drone from returning to a state of high emotional stimulation which deactivates its higher brain functions to prevent it from breaking the Collective's control. The cortical nodes technology is much too advanced and complicated to repair that the Collective themselves choose to simply replace a malfunctioning Cortical Node in the event of a failure or damage. (VOY - Imperfection)