The Gerbil Took the Top Head mission in Control AWE is one of the expansion's most surreal missions. That says something given how weird the game from Remedy Entertainment is, but when you consider what the quest entails, it's weird.
You can access the Gerbil Took the Top Head mission once you force Shaded Hartman to retreat to the Fra Mauro AWE area. Once gone, make your way to the holding cell in the middle of the room next to the moon landing vehicle.
If you talk to the prisoner inside the cell - which doesn't make sense due to his scrambled English - you'll be tasked with bringing him a specific item. There are five items in the Fra Mauro AWE room that you can try to give to the prisoner. Each item is located in a different research office within this room. Take each of them in turn and try to give them to the prisoner through the hatch of the holding cell.
After trying all five elements, the prisoner will tell you that he wants you to find the “head”. To do this, go to the head office of the sector. You can retrace your steps to the first room in the Investigation Area or get there quickly using one of the checkpoints you should have activated during the AWE expansion.
Once you're there, you need to fight a Hiss soldier known as Ranger Sergeant Hooton. They're a level nine enemy, so they can do significant damage to you if you're not careful. Use the pillars in the middle of the room to hide behind, and dodge every now and then to fire your service weapon or throw items at them.
Once Hooton is defeated, levitate into the room they were in. Take the space suit helmet off the desk and quickly return to Fra Mauro. Give the helmet to the prisoner to complete the mission and receive your rewards.