Rey's brain is a quest item in Fallout: New Vegas.
Characteristics
It is one of three possible replacement brains for Rex in the quest Nothin' But a Hound Dog. If it is used as a brain for Rex, he will have an increase in attack power.
Location
It can be bought from Old Lady Gibson at Gibson scrap yard for 700 caps (free with a Barter check of 70). This item can also be gained by killing Old Lady Gibson's dog Rey and taking it off of his body.