Thought Control

 is a Fallout 3 quest that is added to the game with the Point Lookout add-on.

Talk to Desmond
Desmond reveals the brain to be Professor Calvert, he tells you about his past with Calvert and the Calvert family in general. He then tells you to plant a Cogwave Jammer on the Ferris Wheel that will disrupt the messages that Calvert has been trying to send throughout the Point Lookout area. Once you near the Ferris Wheel, you can hear Calvert’s voice trying to persuade you to destroy the device that Desmond gave you. There can be an error here though. When you walk up to the ferris wheel, Calvert may have not contacted you, the Cogwave Jammer can not be placed. This can be fixed by roaming the area, specifically to the item shop, and then you will be able to make the choice.

To plant or not to plant
Once you reach the ferris wheel, you have two options, but don't worry too much about them, they have no effect on karma or main storyline. Desmond, however, will react differently depending on your choice:

Side with Calvert

 * Destroy the jammer. Follow Calvert's instruction to place it in a nearby trash compactor. Calvert will tell you to return to the mansion, which is then destroyed in a huge explosion. There is minor loot in the Panic Room (including ammo, food and a Nuka-Cola Quantum), reached through a hatch in the center of the ruins.
 * You'll then advance to the same place as the second decision, the lighthouse, and the actual decision of who to kill is basically delayed via dialog until the very end. Also, you'll find Desmond isn't dead, but following Calvert in the lighthouse to kill him. Technically speaking this is the better karmic decision (although no actual karma is granted or removed) since you save the tribals and Desmond lives anyway, but you can still loot fingers off of any Tribals you kill (making them bad NPCs), which actually makes Desmond's option not only the better karmic decision, but also the more profitable one if you have the Lawbringer perk.

Side with Desmond

 * Plant the jammer and activate the Ferris wheel. After this is done, Calvert's voice breaks up as the jammer does its job, then a group of Tribals will attack you, and all unnamed Tribals remaining at the Cathedral will become hostile (the named Tribals will likely join them if a fight breaks out unless the unnamed tribe members are killed unobserved).
 * Return to Desmond. When you approach the Calvert Mansion, it immediately explodes. As a result of the explosion, you are knocked to the ground. Once you stand back up, walk to the middle of the house and find Desmond in his panic shelter. He begins to tell you how angry he is that his dogs were killed and that Calvert was so close to the mansion. He then states that the 200 year long feud between him and Calvert is going to end right now.

Notable Loot
Near the end of this quest you will get to Calvert's Lab, located underneath the lighthouse (accessed by a secret passage that will open only when you visit the lighthouse after Calvert Mansion is destroyed). There you will find a good amount of all kinds of energy weapons ammo: Energy Cells, Microfusion Cells, Electron Charge Packs, and even Mesmetron Power Cells! (which may be the hardest to find ammo in the game... even more for free). There you can also get the Microwave Emitter, a weapon that looks identical to the Mesmetron but deals a considerable amount of damage, and uses regular Microfusion Cells as ammo. It is located at the room across Calvert's brain, where the exit ladder is located.

Bugs
Even after destroying the Cogwave Jammer in the trash compactor, you can still walk up to the Ferris wheel and it has the "Activate Ferris Wheel" option, which if you click it it says "The Cogwave Jammer has been installed.", when it really hasn't been. (All Versions)

Rarely when the tribals spawn to attack you for installing the Cogwave Jammer, one will spawn inside the walls. They spawn in the "preservation shelter" inside the wall with The Brain's script and continually kill him(he is flagged essential). To solve this, you must turn off clipping mode with the console command "tcl".

Reward
300 XP

250 Caps after completing a speech check. After hearing the voice of Professor Calvert, you can return to Desmond and extort 250 caps from him.

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