Abnormal brain

Quite possibly a human brain. The color doesn't seem quite right and the left hemisphere of the brain has caved in on itself. These one of the brains that can be found at Sierra Army Depot and used to build Brain Bot. However using an abnormal brain makes Brain Bot so stupid that it can only act as a pack horse. Although you can issue commands to it, it will not leave your party unless you kill it.

Appearances in games
Abnormal brain only appears in Fallout 2.

Possible references
Abnormal brain is most likely a reference to the Abby Normal / Abnormal brain featured in the Mel Brooks comedy film Young Frankenstein (1974).