Understanding our Brain Operating Systems

The Triune Brain

The Triune Brain Model was first developed in the 1950s by neurologist Paul MacLean. It proposes that we have three brains, not one brain. Each brain represents a distinct evolutionary stage.

Reptilian Brain – the Oldest

The oldest is the Reptilian brain, which includes the brain stem and cerebellum. This brain controls muscles, balance, and autonomic functions, such as breathing and heartbeat. It is focused on physical survival and is rigid, obsessive, compulsive, reactive, and fearful. It has the same type of archaic behavioural programs as snakes and lizards. It is “filled with ancestral memories”. It keeps repeating the same behaviours over and over again, never learning from past mistakes. This brain controls muscles, balance and autonomic functions, such as breathing and heartbeat. This part of the brain is active, even in deep sleep.

The Mammalian Brain was next to evolve

The Mammalian Brain corresponds to the brain of the most mammals, and especially the earlier ones. It was referred by MacLean as the “limbic system” or the “mid-brain”. It is made up of the amygdala, a more refined alarm system for danger than the reptilian brain, the hypothalamus, the pituitary, and the adrenal glands. Together they coordinate our most basic fight-flight-freeze responses to protect us from harm and assist with our social survival. When the sensory systems detect stress, the hypothalamus reacts by sending a signal to the adrenal glands, which then triggers adrenaline to go into our bloodstream.

It is also known as the “emotional brain”. It is concerned with instincts, feeding, fighting, fleeing, and sexual behaviour. As MacLean observes, everything in this emotional system is either “agreeable or disagreeable”. Survival depends on avoidance of pain and repetition of pleasure.

The newest brain to evolve is the Neocortex


The Neocortex is also known as the thinking or rational brain. Sometimes it is referred to as the “Executive Center.” This contains the higher cognitive functions that distinguish humans from animals, such as speech, memory, understanding, creativity, musical ability, empathy, kindness, awareness, and the ability to interpret and assign meaning to life activities. The cortex is divided into left and right hemispheres, the famous left and right brains. The left half of the cortex controls the right side of the body and the right side of the brain the left side of the body. Also, the right brain is more spatial, abstract, musical and artistic, while the left brain more linear, rational, and verbal.

MacLean refers to the cortex as “the mother of invention and father of abstract thought”. In Man the neocortex takes up two thirds of the total brain mass. Although all animals also have a neocortex, it is relatively small. A mouse without a cortex can act in fairly normal way (at least to superficial appearance), whereas a human without a cortex is a vegetable.

The Good News is the Brain is ReProgramable

The concept of neuroplasticity has replaced the formerly-held position that the brain is a physiologically static organ, and explores how – and in which ways – the brain changes in the course of a lifetime. Our Brain is more flexible than we’ve ever thought before.
It changes because it is constantly optimizing itself, reorganizing itself by transferring cognitive abilities from one lobe to the other, particularly as you age. After a stroke, for instance, your brain can reorganize itself to move functions to undamaged areas.

“What fires together, wires together”
Rick Hanson, neuroscientist and author “Buddha Brain”