Our Triune Brain: The Reptilian, Mammalian, and Neo-Cortex

Our triune brain is a masterpiece of evolution. Evolution is the reason that we have three brains in one. Our brain showcases our journey from reptiles to mammals to human form. It has reptilian brain stem, mammalian or limbic system and a state of art neo-cortex.

The Reptilian Brain Stem

The reptilian brain stem is the first brain to develop in the womb. It controls our basic body functions and primitive survival circuits. Heart rate, digestion, breathing, elimination of waste are all regulated by the reptilian brain stem. This part of the brain can remain in action even when the other parts of the brain stop functioning and a person is declared brain dead. It is called reptilian brain because it evolved millions of years ago and is more like the entire brain of present-day reptiles.

It has a predominant survival circuits that control “fight or flight” responses of the autonomic nervous system. Our sympathetic nervous system comes into action whenever we face a sudden or imminent threat. Like when we are walking on the road and a car suddenly comes in front. In such a situation our body gets a surge of adrenaline and other stress hormones. This surge of adrenaline enables us to act swiftly and respond to danger. Once the danger has subsided, the sympathetic nervous system takes a backseat and parasympathetic nervous system gets into action. It helps us to revert to our original state of rest called homeostasis where we regain our calm and balance.

Triune Brain: Reptilian Stem, Limbic System and Neocortex

The Limbic System or Mammalian Brain

This mammalian brain or limbic system is the next brain to develop in the womb. The limbic system is responsible for our emotions and bonding. All emotional learning takes place in this part of the brain. Mammals, be it a rat or a cow are known for their bonding with their young ones. Reptiles, on the other hand, do not bond with their progeny. They abandon their young ones after birth to fend for themselves. Some reptilian species even devour their young ones.

The limbic system also greatly expands on the survival circuits of the reptilian brain stem. Amygdala located in limbic system is responsible for the perception of emotions such as fear, anger, and sadness. Amygdala amplifies the danger signals of the reptilian brain by evoking emotions of fear and anger. It stores memories of events and emotions so that an individual may be able to recognize similar events in the future. For example, if someone has been bitten by a dog in childhood, she would be more alert and cautious around dogs in future as well. The bigger size of the amygdala correlates with increased aggression and physical behavior.

The Neo-Cortex: Acme of Human Achievement

The neocortex is the third brain to develop in utero. It represents the acme of evolution. Neocortex controls all that differentiates human beings from the rest of living species. It is involved in higher mental functions such as sensory perception, cognition, memory, generation of motor commands, spatial reasoning, conscious thought, and language.

The most important part of the neocortex is prefrontal cortex also referred to as the fourth brain. It controls executive functions, creativity, reason, problem-solving, logic, abstraction, insight, and morality. It helps us to regulate our emotions, to postpone immediate gratification for the sake of the future goal. This part of the brain develops only after birth. In human neocortex constitutes 30% of the brain whereas in cats it is just 3%. Chimpanzees our closest living relatives have 11% of the brain as the neocortex. The neocortex is the ultimate director of all the three brains.

Nurturing Human Brain

The brain is the most sensitive organ of the body and therefore it is encased within a hard skull. The size and quality of an infant’s brain depend upon the mother’s emotional state. An emotionally secure mother would give birth to a baby with an enlarged neo-cortex and a small reptilian brain. Whereas an expectant mother who is anxious and stressed would give birth to a baby with a relatively larger reptilian brain. The mother’s emotional state continues to affect the development of the brain even after birth.  The first two years of a child are vital for the brain growth as 90% of the brain growth happens during this time.

Our triune brain is the best example evolution. As Dr. Brant Cortright puts it, ” Optimal brain development gives us access to our animal inheritance- the reptilian circuits and mammalian capacity for emotion – together with our reason and intelligence”