Brainless

Brainless is a special 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 add-on, they are unlocked in the course of the conversation.

Effects
The head is immune to crippling, +5% to DT (minimum 1) and a +25% resistance to chem addictions.

Behind the Scenes
The term "brainless" refers to lack of wit and, in simple terms, means "stupid." This vernacular meaning of the term itself, however, has no bearing on the perk and its effects.