Cranium design
From Tardis Wiki, the free Doctor Who reference
Lacking the side handles of his Cyberman drones, the Telosian Cyber-Controller possessed a "special cranium design" which gave him his enhanced intelligence. (PROSE: The Powers Behind the Throne, TV: The Tomb of the Cybermen) He retained his enlarged cranium even after his Cyber-body was modified to the Neomorph form. (TV: Attack of the Cybermen, AUDIO: The Ultimate Cybermen)
