neocortex

By Robert Sapolsky

Reptilian brain

Also known as the primal brain, this is the oldest part of the brain and is responsible for basic life functions like breathing and alerting us to danger. It’s also responsible for the fight or flight response.

Limbic system

Also known as the paleomammalian brain, this part of the brain is responsible for emotions and is involved in learning and memory. It’s based on instinct and past experiences.

Neocortex

Also known as the neomammalian brain, this part of the brain is responsible for higher cognitive functions like reasoning and logical thought. It’s the outermost part of the brain.

Video by Robert Sapolsky

These three parts of the brain are often described as working together to keep us alive. However, the triune brain hypothesis, which describes the brain as having these three components, has been criticized and is no longer widely accepted by comparative neuroscientists.

The neurologist Paul MacLean has proposed that our skull holds not one brain, but three, each representing a distinct evolutionary stratum that has formed upon the older layer before it, like an archaeological site. He calls it the “triune brain.” MacLean, now the director of the Laboratory of Brain Evolution and Behaviour in Poolesville, Maryland, says that three brains operate like “three interconnected biological computers, [each] with its own special intelligence, its own subjectivity, its own sense of time and space and its own memory”.