Your singular human brain functions like a three-member committee. Each of your three primary modules includes many distinct submodules that in turn contain even smaller submodules, and the interactions among these modules and submodules are so fast, so complex, and so overlapping and interconnected that your brain can hardly even begin to understand its own inner workings.
Your oldest primary module, sometimes called the primitive or reptilian brain, includes your brain stem and cerebellum. It controls your basic bodily functions, including a highly evolved set of unconscious reflexes and responses to novelty or danger: alertness, hunger, thirst, sexual desire, anxiety, fear, terror, panic. This instinctive brain comes online before you are even born, and its job is to keep you alive in a dangerous world.
Next, shortly after birth, a second member of your brain committee wakes up and becomes engaged. This mammalian or limbic brain module orients you toward attachment by generating emotions that strengthen relationships, relationships that are necessary for a helpless infant’s survival. The need for connection, for example, draws you toward caregivers who offer comfort, companionship, and protection. Feelings of affection and loyalty keep you from easily discarding these essential relationships. Like the reptilian brain, this mammalian brain operates at super-high speeds, deeper and faster that you can consciously keep track of. For that reason, we can call this second member of the brain committee the intuitive brain.
Before you even learn your name, before you are even conscious of your own existence as an individual, your instinctive and intuitive brains are already hard at work, forming connections, learning to work together, keeping you safe, and keeping you connected with those upon whom your survival depends. Then, gradually, especially after the age of about two, your third brain committee member, consisting of the neocortex and its components, begins to assert itself. Often called the primate brain, it’s the logical, rational, analytical member of your brain committee. This module is the seat of intellect, and it enables you to use language and to think critically and creativity. This intellectual brain is essential to help you become both an independent self and an interdependent agent in human society.
People sometimes refer to these three committee members as the gut (the instinctive brain), the heart (the intuitive brain), and the head (the intellectual brain). We could also refer to them as the survival module, the belonging or relational module, and the meaning module. When we speak of healthy, mature, or well-rounded human beings, we are referring to people who integrate their survival, belonging, and meaning modules (and all their submodules) in ways that bring benefit and pleasure to themselves and others.
From “Faith After Doubt: Why Your Beliefs Stopped Working and What To Do About It” by Brian McLaren