A synaptic transceiver was a device invented by The Doctor in an alternate 2392, for use in piloting a vessel equipped with a neural interface. Implanted in the cerebral cortex, the device allowed synaptic interface to be established between the user's mind and the vessel's controls.
In 2404, Admiral Kathryn Janeway from the alternate timeline utilized a shuttle equipped with such an interface to travel back in time to the year 2378, on a mission to alter history and return the USS Voyager to the Alpha Quadrant sixteen years early. Later, the admiral utilized the interface to communicate with the Borg Queen, as part of her plot to destroy the Collective. (VOY: "Endgame")