Left Brain Right brain.
The "lizard brain" is a colloquial term, often used metaphorically, to describe the most primitive part of the human brain, the brainstem and cerebellum, which is responsible for basic survival functions and instinctive behaviors. It's associated with the limbic system, a set of structures including the amygdala and hippocampus, that deal with emotions, memory, and motivation. While not a literal "lizard" brain, it's a useful concept for understanding how our primal instincts can sometimes conflict with more rational thought.