No, you don't have a Lizard brain in you | A modern myth about brain | - Taking Notes #1

This is a new blog series called "Taking Notes" that I am starting. Here, I'll be summarising things I learn on a daily basis. My goal is to write a blog under this topic at least 3-4 times a week.

I've started reading "Seven and a half lessons about the brain" by Lisa Feldman, a neuroscientist who I got to know about through Sam Harris' recent podcast. This blog is highly inspired by the first chapter of that book.

Humanity has been believing in the "Triune" theory of brain for a long time. Although it has been disproven decades ago but people still preach this theory. I have myself read about this theory as a kind of "fact" from reputed sources. This is actually a modern myth. This myth was started by philosophers like Plato, and recently popularised by Carl Sagan in 1977. 

Plato said that our mind has 3 parts. One controls survival instincts, like hunger and sex drive. Second controls emotions. And third controls rationality. Plato said these 3 parts are in constant conflict with each other.

People through history then started to theorise that since we are evolved from reptiles i.e. once our ancestors were reptiles like lizards, our brain has a lizards brain as core, which is the part that controls survival instincts. And with evolution a layer of brain was added on this Lizard brain and the brain of pre-historic mammals was formed. Now this new layer was called limbic system, which controlled emotions. So now these mammals were also capable of emotions along with survival instincts, which reptiles lacked (according to this theory). Then came the topmost layer that modern mammals (mainly humans) had, Cerebral cortex, which made us capable of thinking, specially rational thinking. This layer is what makes humans different.

Later in mid 20th century someone (sorry, I don't remember the name) examined a human brain with whatever technology was present at the time, which was mainly microscope. And then compared it with reptile brains and found similarities between our lower brain and reptile brain. And concluded this theory to be true. People widely accepted this theory, to the extent that it is still famous and discussed, although it's been debunked decades ago.

Scientists recently found that our brain are fundamentally similar to that of reptiles. Overall most animals share fundamentally same type of brain. All of them have all three layers (reptile brain, limbic system, cortex). The only difference is that they have it in different proportion. Humans have larger cortex than lizards and other reptiles (by large, I don't mean the absolute size, but size campared to other parts of the brain) which means that even lizards have the cortex (the rational brain) that we thought they lacked, but proportionally smaller.

Most animals have the potential to have brain parts as large as humans (again, I mean large proportionally, not absolutely), but they don't. The size of brain parts is decided during the growth period of embryo. In due course of evolution, different animals adopted different size of brain parts. For instance, our cortex grows for much longer time during human embryo period compared to lizard's embryo period, which results in larger cortex in humans than in reptiles.

So there you go. This was about the modern myth of "Triurne brain". Next time someone explains you how you have a Lizard brain, educate them. Spread the knowledge.