Regions and Layers of the Brain

Lesson objective:

In this lesson, we outline some involuntary intrinsic automatic functions by specific parts of the brain near the brain stem. The basic functions of the brain stem include involuntary processes such as heartbeat and breathing. The limbic system is responsible for body state awareness, learning, and memory aspects. The modern cerebral cortex is responsible for logical conclusion, strategic thinking, sensory perception, logic, location, and active memory.

We have learned a lot about the human brain by studying the brains of animals. We know that we, as a species, share certain functions and brain regions with even tiny animals. For example, all mammals breathe. 

All mammals have a heartbeat and a somewhat similar circulatory system. Some of those automatic, core, involuntary functions are coordinated by specific parts of the brain near the brainstem. The brainstem, at the base of the brain, is something we share with most animals. 

Think of it like the rings of a tree. The rings of a tree are evidence of its age, size, functions, and past experiences. Tiny, young trees have fewer rings. Thick rings indicate a period of growth. Thin rings indicate a period of short growth. Brains are similar. 

For example, core brainstem functions like heartbeat and breathing are shared across species. We and all mammals all have a brainstem, because we all breathe and circulate blood. In the same way, all trees have an innermost ring, a center and “origin” point of the tree. The innermost ring is not necessarily more or less important than the other rings, but it was the first point of growth and communication for water and nutrients.

In the human brain, the brainstem is physically contained in the innermost part of the brain, like that innermost ring of a tree. And, in some animals, you would find little more than a brainstem. Worms have a bundle of neurons that have some brainstem functions. Snakes have a brainstem and some other features that we humans also have. Essentially more complex functions developed around the brainstem, physically connected and extending outward, like the rings of a tree. 

Similarly, since all animals try to stay alive, they have brain functions that alert them to threats, to new survival resources, and to risks to those resources. Some, but fewer, animals can solve puzzles. Some, but even fewer, animals can feel something similar to human emotions (happiness, sadness, surprise, anxiety). The pattern is clear: the brains of different animals are suited to the complexity of their lives.

To a certain extent, the parts of the brain responsible for basic functions and processes are contained at the core. From the core outward are parts of the brain most often responsible for more complex, abstract functions. In short, from inner to outer we move from basic survival functions to more complex, deliberative functions. It’s not a perfect match, but it helps understand quite a bit of how our brains are structured. 

It is important to reiterate that our brains are interconnected in complex networks. The fact that our brains have different “layers” or regions does not mean that simple functions exclusively rely on inner brain regions. Similarly, complex thinking tasks do not exclusively rely on “outer” regions. Like the elephant and the rider, and like the airport control tower, healthy functioning requires constant communication between all parts

Multiple times, we have stated that the brain’s priority is to help you stay alive and to help you successfully navigate the world. In order to survive, you need to do more than just breathe, eat, and have blood in your veins. You need to be able to think, solve puzzles, and communicate using language.

But, in general, we can say that innermost parts of the brain do have some core functions, while outer parts tend to specialize in different functions like spatial reasoning, language, and many aspects of cognition and reasoning.

But which is more important? You can survive, for a short time, without thinking or even having feelings, but you can’t survive without breathing. So, while all our brain’s functions coordinate to help keep us alive, those functions most critical to survival are most often contained in the innermost areas of the brain. In this way, the structure of the brain generally reflects the ranked building blocks of survival.

And again, while the brain is intricately interconnected, for some people it helps to think of three different and complementary levels or networks, with each level having some very similar responsibilities. 

First – The brainstem, which is responsible for basic functions such as heart rate, breathing, sending messages from the brain to the body, and blood pressure.

Second – the limbic system or limbic circuitry, which is responsible for awareness of the state of the body, aspects of learning, memory, awareness of fear and threats.

Third – the third level, the neocortex, and specifically the prefrontal cortex which is responsible for logical reasoning, strategic thinking, perception, logic, location and working memory–many advanced cognitive tasks. 

The images of the airport control tower, the elephant and the rider, and the layers of the brain help us understand that there are functions in the brain below our conscious control, and there is a constant and delicate balance between what we control and what we do not control in the brain. 

We don’t control our beating hearts consciously. We don’t control what we feel, emotionally, all the time. We desperately need these functions though, as they give the necessary fuel, time, and resources to the “rider” to handle aspects of higher thinking and analysis. And remember, all of these functions are deeply integrated, and we will explore how they work together specifically in the context of stress and trauma.