The Triune Brain

I spent the weekend reading ‘A General Theory of Love’ by Tomas Lewis, a psychiatrist. He writes beautifully; it’s the sort of engaging, readable popular science book that I just find irresistible. Fortunately there seems to be a never ending stream of these books; enough to keep me satisfied for a long time.

Lewis describes the brain as ‘triune’. That is to say, split into three parts, the reptilian, the mammalian and the human brains.

The reptilian brain is the brain stem: this part of us has existed, in evolutionary terms, before we even became mammals. It is responsible for the regulation of our bodily systems, heart rate, breathing rate, hormone levels and so on.

The next part is the mammalian brain. This is the limbic system wrapped around the top of the brainstem and tucked underneath the big outer part. The limbic system is the bit that is difficult to make sense of in diagrams of the brain and is responsible for our emotions. This part allowed emerging mammals to care for offspring and form communities.

The final part is the human brain which is the largest part. The big outer layer of grey cells with its delicate convolutions and complex white matter is the image that people think of when they think ‘brain’. This is the thinking part, the part that gives us language, maths and abstract thought.

Ever wondered why one can think one thing and feel another? Why they seem so separate? The answer is because they are. They are entirely different sections of the brain. It is the emotional, mammalian brain that gives rise to our emotions. ‘Emotion’ is derived from the Latin word to move. It is our emotions, not our thoughts, which generate our actions on the whole. This is why self-help books rarely work (reading is a human brain activity) and strategies like hypnosis really do. By appealing directly to the emotional brain under hypnosis it is possible to bring about change in behaviour quickly.