Brainless

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

Obtaining
In the initial dialogue with Doctor Klein as part of the quest Welcome to the Big Empty, 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
Your head can no longer be crippled, your Damage Threshold is raised by 5% permanently, and you have an added 25% resistance to chem addictions.