The last century has enabled us to learn a great deal about our brain and how it functions. However, as many of these ideas are recent theories, we find ourselves confronted with differing theories and definitions. Also consider the different fields of interest related to the brain. They will determine their most relevant theories, what is mentioned, and what is not.

At the same time, theories that are now considered outdated continue to exist in the popular descriptions of the brain. Paul D. MacLean’s triune brain theory gave us an early evolutionary view of the brain. He described three somewhat separate brains and introduced the term “limbic system.”

From a psychological perspective, these three brains determine how responsibilities are distributed in the brain.

The reptilian brain is considered the oldest of the three. It is located in the brain stem and is seen as the one caring for the things a newborn can do. It is truly basic stuff: eat, sleep, cry, breathe, wake, feel temperature, hunger, wetness, and pain. It also assists the body in getting rid of toxins by urinating and defecating. It’s the part of the brain that is active when a child is born.

Directly above the brain stem is the hypothalamus. Together, they coordinate the activity of different organs, ensuring that basic life-sustaining systems remain functional.

The reptilian brain is considered the oldest part. It is vital for the brain’s main task: ensuring survival independently of circumstances.

Immediately above the reptilian brain is the limbic system. In caring for our survival, it is the arbiter of what is important for survival, the seat of the emotions, the monitor of danger, and the judge of what’s pleasurable and scary. As a central command post, it is responsible for coping with the challenges of living within our complex social networks. It may activate fight, flight, or freeze reactions. The development of the limbic system truly starts once the child is born. And in this event, it is considerably shaped in response to the experience the baby has in its first environment. The environment isn’t responsible for everything. The limbic system’s evolution is also shaped by the child’s genetic makeup and inborn temperament.

The third part of the brain, the rational brain, is located as a third layer on top of the other two. To enhance our survival ability, it is concerned with the world outside of us. It seeks to understand how things and people work and tries to figure out how to accomplish our goals, manage our time, and sequence our actions.

Considering this structure of three brains, it becomes understandable that the brain’s capacity to prioritize survival is closely connected to its ability to shut down any part of the brain that is not relevant for survival. It will do so when it perceives the need to act in the service of survival. But the brain is also subject to the way these parts of the brain work together as a system. That is especially true when the rational brain tries to substitute itself and its logic for the other two systems. It then seeks to perform beyond the signals the reptilian brain and the limbic system provide. The rational brain then discards data relevant to the other two, establishing a tension between the different systems. Thus, for example, losing the baby’s ability to spontaneously manifest its bodily needs inviting its caretaker to address them.

There is much more that could be said, but the above may suffice to imagine how the story we tell ourselves emerges. It can be conceptualized as a result of the different responsibilities attributed to parts of our brain. Parts that develop themselves one after the other while acting as the system, we call our brain.