Lump of brain

 is an item that the Lone Wanderer finds in the Point Lookout add-on for Fallout 3. It is a piece of the Wanderer's own brain in a glass jar.

Location
The item is in the Engine Room of the Duchess Gambit, on the table next to Tobar. You can only get in this room after completing the quest Walking with Spirits and speaking to Nadine in the The Ark & Dove Cathedral.