The History of Neurological Dominance

Although neuroscientists argue about the degree to which different parts of the brain perform specialist functions, it is known and widely accepted that some specialisation exists. As far back as the age of Hippocrates (460-370 BC), physicians knew that the brain consisted of two halves. They believed that the left side was the essential half but that the right side was a defunct throwback to some bygone era of human development. In the 1860s the French neurologist Paul Broca discovered that a portion of the left hemisphere controlled the ability to speak language and a decade later a German neurologist made a similar discovery regarding our ability to understand language.

The breakthrough in understanding the right hemisphere came in the 1960s and '70s when Roger Sperry discovered that, far from being defunct, the right hemisphere of the brain simply processed information in a different way: Where the left side processed information sequentially, the right side processed it simultaneously; where the left side recognises a persons name, the right side recognises their face; where the left side is good at logic and analysis, the right side reasons holistically, recognises patterns and interprets emotions and non-verbal expressions.

Also in the 1960s, the neurologist Paul MacLean was looking at the evolution of the human brain. He concluded that our skulls hold not one brain, but three, each representing a distinct evolutionary layer that has formed upon the older layer before it.

The idea that these three brains are somehow separate is now regarded as being incorrect, but it is interesting how the notion of three levels of consciousness exists in some ancient spiritual traditions. Gurdjieff for example referred to Man as a "three-brained being". There was one brain for the spirit, one for the soul, and one for the body. Similar ideas can be found in Kabbalah, in Platonism, and elsewhere, with the association spirit - head (the actual brain), soul - heart, and body in the belly. The three brains of MacLean’s work have sometimes been referred to as the "lizard, leopard and learner" brains. MacLean described them in the following ways:

• The Reptilian Brain – This is the part of the brain we have in common with reptiles. It sits at the bottom of the skull just on top of the spinal column and is responsible for controlling the muscles, balance and autonomic functions such as breathing.
• The Mammalian Brain – Often called the limbic system, this is the part of the brain we have in common with mammals. It is the source of our emotions and deals with fight or flight instincts.
• The Learning Brain – Sometimes called the "Late Mammalian Brain", this part of the brain is most highly developed in the primates, particularly humans. It is involved in the higher functions such as sensory perception, spatial reasoning, conscious thought and language.

When considering Neurological Dominance, we can discount the reptilian brain as it is not involved in our consciousness, only in regulating our physiology and controlling out automatic bodily functions. This leaves us with the learning and the mammalian brain which are more accurately referred to as the cerebral and limbic systems.

By combining the work of Sperry, MacLean and their colleagues we can see that our conscious brains consist of four main processing centres; the cerebral left, limbic left, cerebral right and limbic right.  Because each of these parts of the brain process information in different ways, the preferences we have for using some parts of the brain over others is what shapes our lives and creates the physiological foundations of our personalities.

An understanding of the subject of Neurological Dominance can therefore help us to understand why we are the way we are and in what ways other people might differ.

Additional reading:

What are the thinking preferences of the different parts of the brain?
How does the brain grow and develop dominance?
How can Neurological Dominance be measured?