Brainless

 is a perk in the Fallout: New Vegas add-on Old World Blues.

In the initial dialogue with Doctor Klein as part of the Welcome to the Big Empty quest, you find out that your brain, heart, and spine have been removed and replaced. This perk represents the replacement of your brain. While you technically have these perks from the start of the DLC, they are unlocked in the course of the conversation.

Effects
The description of the perk reads: "Your brain has been replaced with advanced technologies: Your head can no longer be crippled and is resistant to chem addiction (+25% resistance) and shock from bodily damage (+5% Damage Threshold, minimum 1)."