Fish Brain?

Lower animals (fish, amphibians, reptiles, birds) do not do much "thinking," but instead concern themselves with the everyday business of gathering food, eating, drinking, sleeping, reproducing and defending themselves. Therefore, their brains reflect the major centers that control these functions. We perform these functions as well, and so have a "reptilian" brain built into us.

Underside of the brain, showing the brainstem and cranial nerves