The term "lizard brain" is generally a term that refers to behavioral tendencies based on reflexive instincts and emotional responses rather than advanced cognitive abilities or logical thinking.
The term is based on the "three-brain theory" proposed by evolutionary biologist Paul McLean. According to this theory, the mammalian brain evolved through three stages in the course of evolution. The most primitive part is the "lizard brain", which is responsible for controlling instinctive reactions, aggressive reactions and reproductive behavior.
On the other hand, the "mammalian brain", which developed with the evolution of mammals, is responsible for social behavior, emotions, memory, language, logical thinking, and cultural activities.
The "lizard brain" is sometimes used in modern society, when emotional reactions and instinctive actions play an important role. For example, reactions in stress or crisis situations.