Gray Matters

 is a perk found in the data files of the Fallout 3 add-on Point Lookout. It doesn't appear in the game and can only be obtained with console commands.

Protect what is important. With the ability brains, damage to your head will be reduced by 25%.

Trivia
"Grey Matter" is a slang term/colloquialism for a person's brain/brain matter.

The perk name implies that it was to have been gotten during the Walking with Spirits quest, along with the Punga Power! perk. The benefit description also makes a humorous joke at the lobotomy; given that afterwards there isn't as much to damage, hence the damage reduction.