The Cortex Machina project has its origins in a deeply rooted fascination with neurobiology in general, and the biological origins of consciousness in particular. Unfortunately, it can often be very challenging to discuss and share these fascinating concepts, simply because they generally require a lot of prior knowledge which is, to say the least, quite unfamiliar to most people. That’s why we have started this series of short columns: to kindle interest in the fields of neuroscience and neurobiology and to provide my readers with enough general knowledge on the human brain and cognition to start exploring and sharing these fascinating concepts themselves. We will start with a series of articles on brain anatomy, to provide the reader with an understanding of brain architecture and nomenclature, which will be helpful later on when we discuss other topics. So without further ado, let’s get into the major divisions of the brain.
What are ‘Brains’?
The brain is a peculiar organ. With only 1.5kg of white, grey and glial matter it manages to control all the function of our bodies, interprets the outside world, gives rise to consciousness, controls memory and speech and, in humans, generates our minds and sense of individual self. It is the product of hundreds of millions of years of evolution, first arising as simple nerve nets in the first multicellular organisms over 500 million years ago and then evolving into ever more complex nervous systems in a relentless arms race driven by natural selection.
Brains are found all over the animal kingdom, even among some animals lacking a nervous system altogether but still having the ability to circulate electrical impulses in other ways (for instance the ‘glass sponge’). In this column however, we will focus more specifically on the brains and nervous systems of the animal Class of ‘Mammalia’, i.e. mammals. This Class of Mammalia is of particular interest because it includes our own species, Homo sapiens, and the evolution of the brain in this lineage has been particularly impressive.
The brain constantly receives information about the outside world through its sensory systems and combines this with memories about prior experiences and with input from subconscious neural processes to generate an image of the world surrounding us. This constantly updating image in our heads is what we’d call our ‘conscious experience’. But to start understanding “how” our brain does all this, we first have to get a grasp of basic human brain anatomy (and by extension most placental mammals).
Brain Architecture
The brain is just one part of our nervous system, which is composed of the central nervous system (containing the brain and the spinal cord) and the peripheral nervous system (‘spinal nerves’ branching from the spine and ‘cranial nerves’ branching from the brain).
The brain itself, defined as the part of the central nervous system contained in the skull, can be divided in a number of different ways. Labels and divisions are tools to make it possible to talk about the brain in meaningful ways, and depending on your field of study, different divisions and classifications can be useful. Table 1 below presents two of the most common “divisions of the brain” that are in use:
I personally prefer to use the division based on nervous system development as the division based on physical appearance doesn’t reflect well the actual biological divisions between neuron clusters and basically leaves out the whole diencephalon. So it’s this classification in “Forebrain, Midbrain, and Hindbrain” that I will present here. To better appreciate this classification system, let’s observe how our nervous system starts out in the early development in the womb and compare it with the nomenclature used in table 1:
Our whole nervous system starts out as a neural tube, which divides into three vesicles which in turn give rise to the three major divisions of the brain: forebrain, midbrain and hindbrain (see Fig.2). Later on these three vesicles subdivide into a further 5 sub-vesicles: the telencephalon, diencephalon, mesencephalon, myelencephalon and metencephalon. These 5 vesicles in the neural tube, present at the start of the development of the nervous system in the womb, end up forming all the cortical structures of the brain. Table 1 lists some of the principal structures in which ‘vesicles’ they are generated during embryonic and fetal development.
A big thanks for your reading from the entire Cortex Machina team!
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