Triune-Brain Theory

Triune-brain theory, a largely outmoded, but still popular evolutionary theory of brain development emphasizes three key brain regions that function relatively independently in coping with stress. The theory suggests the brain regions evolved separately and function somewhat independently. It was used to explain the evolutionary basis of anxiety. It focused on fear reactions in adults and older children to actual dangers in the environment, suggesting strategic decisions to avoid danger and harm were made at all three levels of the triune forebrain. It sees brain evolution in stages:

• First, instinctive (reptilian) involving basic behavioral responses: basic ganglia and brainstem triggers fight-or-flight response (FFR), as well as movement and basic life functions.
• Second, emotional (paleomammalian) limbic system, evolving emotional responses to alter basic responses when faced with threat or challenges. More prominently in mammals than reptiles.
• Third, rational (neomammalian) cortex, with cognition and executive functions to alter emotional responses using reason, logic, and planning. When rational brain fails to deal with threats of danger, brain activates more primitive de-escalating strategies, which become anxiety disorders. Most prominent in humans.