Evolution of the Brain: Three Functional Layers

Very, very early in evolutionary history, simple "beings" had brainstems that regulated autonomic function and kept them alive. Human beings still have a brainstem, located just above the spinal cord, which tells our lungs to breathe and our hearts to beat. Similar in architecture to the brainstem of reptiles, the human brainstem it is sometimes called the reflex brain or the first brain. We can summon it to conscious awareness, although it usually functions automatically.

The limbic system or emotional brain is thought to have developed out of the first brain. It helps us store and remember past experiences and learn from them. The limbic system in humans is located in the approximate center of the brain; when information enters the limbic system, we experience bodily sensations, transmitted by the peptides or chemical information substances, in the form of a "reaction" to the stimulus with much more awareness of what is happening than at the level of the first brain.

Out of this limbic system came the rational (thinking) brain or thin cortex. The cortex enables us to comprehend sensory information and plan accordingly. The very thin outermost layer of the cortex called the neocortex is responsible for higher order thinking and symbolic communication, art and ideas, and long-term planning. The millions or billions of connections between the limbic brain and the thinking brain allow for the free-flow of information between these layers.