How Is the Brain Structured? A Neuroanatomist Explains

This article is an excerpt from the Shortform book guide to "My Stroke of Insight" by Jill Bolte Taylor. Shortform has the world's best summaries and analyses of books you should be reading.

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How is the brain structured? How does its structure impact its function?

The brain is the most complex organ in the body. Though each part of the brain serves its own function, they all work in tandem to create your sense of self, direct your body’s movements, and generate a coherent picture of your surroundings.

Here’s how neuroanatomist Jill Bolte Taylor explains the brain’s structure.

How Is the Brain Structured?

How is the brain structured? The brain is an intricate parallel processor (a system that can manage many functions simultaneously) composed of billions of nerve cells that are grouped into distinct regions. Brain function depends not only on those regions but on how the nerve cells network and communicate with each other.

(Shortform note: Not only is the brain incredibly complex, but it is also highly malleable—a quality known as neuroplasticity. In The Brain That Changes Itself, psychiatrist Norman Doidge defines neuroplasticity as the brain’s ability to reshape itself in response to both external and internal stimuli. Because of neuroplasticity, our brains’ network pathways don’t only change over time, but can also completely rewire themselves into new patterns.)

The innermost layers of the brain are the oldest from an evolutionary perspective. This is the limbic system, also known as the “animal brain,” which Taylor identifies as the source of your initial emotional reactions to anything you perceive in your surroundings. Surrounding the old brain is the cerebral cortex, which in humans is twice the size of that of any other species. The outermost layers of the cerebral cortex were the most recent to evolve, and they house your abilities for language, logic, and abstract thinking.

(Shortform note: Though Taylor describes the cerebral cortex as the most advanced portion of the brain, that doesn’t mean it’s more important than the rest. In The Whole Brain Child, Daniel J. Siegel and Tina Payne Bryson argue the importance of integrating the upper (cognitive) and lower (instinctive) parts of the brain as we develop in childhood. While the cerebral cortex is essential for its ability to reason and empathize with others, the inner region of the brain is crucial for its “gut instincts” and immediate responses to stimuli. When you swerve out of the way of a sudden car collision, it’s your “animal brain” that just saved your life.)

All parts of the brain are made up of information-transmitting cells, called neurons, which differ from other cells in your body in that they stop growing and replicating when you’re born. In other words, says Taylor, the brain cells you had when you were a baby are the same ones you’re using to read this right now. What changes as you mature is the way those cells connect to each other. As you age, those connections become more complex. They allow for better processing of the neural inputs from your senses, they let your cerebral cortex override your emotional limbic system, and they create new cognitive pathways for data that become ingrained as you absorb new information and practice new skills.

(Shortform note: Modern research shows that the brain’s neural connections don’t simply become more complex as we age; the parts of the brain performing certain tasks can change over time. In The Brain That Changes Itself, Doidge explains that this process begins in infancy when the brain is absorbing vast amounts of new data. Later in life, the circuits of your brain will continue to reshape themselves, and if brain function is lost—as in the case of stroke—the remaining healthy portions of your brain will compete to make use of any nerves in the damaged area that still function.)

The cerebral cortex in which all this occurs has two distinct halves connected by a bundle of nerves called the corpus callosum. The two halves of the brain work in unison but each with its own abilities, perception, and personality. When functioning normally, the two halves of the brain are an inseparable whole, and every cognitive activity—such as reading, talking, painting, or driving—takes place in both hemispheres, with each side contributing to the thought process in a different way.

(Shortform note: The simplified model of the brain that Taylor uses is one that’s generally understood by the modern public. But, in Seven and a Half Lessons About the Brain, Lisa Feldman Barrett argues that it’s overly simplistic, to the point of being misleading. The model gives a false impression that specific regions of the brain control specific bodily functions, when in fact each function is controlled by clusters of neurons networked throughout the brain. Taylor acknowledges this complexity, but nevertheless insists that the different regions of the brain behave and contribute to cognition in different, identifiable ways.)

How Is the Brain Structured? A Neuroanatomist Explains