executed?
Itâs hopeless to answer these questions by studying only brain regions, their sizes, and their activity levels. We must look at the organization of the brain on a much finer scale. A cortical area can contain over 100 millionneurons. How are they organized to perform mental functions? In the next few chapters weâll explore this question, along with the idea that brain function depends heavily on the
connections
between neurons.
Part II: Connectionism
3. No Neuron Is an Island
The neuron is my second-favorite cell. Itâs a close runner-up to my favorite: sperm. If you have never looked into a microscope to see sperm swimming furiously, grab your favorite biologist by the lapels of his or her lab coat and demand a viewing session. Gasp at the urgency of their mission. Mourn their imminent death. Marvel at life stripped down to its bare essentials. Like a traveler with a single small suitcase, a sperm carries little. There are mitochondria, the microscopic power plants that drive the whipping motion of its tail. And there is DNA, the molecule that carries the blueprint of life. No hair, no eyes, no heart, no brainânothing extraneous comes along for the ride. Just the information, please, written in DNA with the four-letter alphabet A, C, G, and T.
If your biologist friend is still game, ask to see a neuron. Sperm impress by their unceasing motion, but a neuron takes your breath away with its beautiful shape. Like a typical cell, a neuron has a boring round part, which contains its nucleus and DNA. But this
cell body
is only a small part of the picture. From it extend long, narrow branches
that fork over and over, much like a tree. Sperm are sleek and minimalist, but neurons are baroque and ornate (see Figure 13).
Â
Â
Â
Figure 13. My favorite cells: sperm fertilizing an egg
(left)
and a neuron
(right)
Â
Even in a crowd of 100 million, a sperm swims alone. At most one will achieve its mission of fertilizing the egg. The competition is winner take all. When one sperm succeeds, the egg changes its surface, creating a barrier that prevents other sperm from entering. Whether brought together by a happy marriage or a sordid affair, sperm and egg form a monogamous couple.
No neuron is an island. Neurons are polyamorous. Each embraces thousands of others as their branches entangle like spaghetti. Neurons form a tightly interconnected network.
The sperm and the neuron symbolize two great mysteries: life and intelligence. Biologists would like to know how the spermâs precious cargo of DNA encodes half the information required for a human being. Neuroscientists would like to know how a vast network of neurons can think, feel, remember, and perceiveâin short, how the brain generates the remarkable phenomena of the mind.
The body may be extraordinary, yet the brain reigns supreme in its mystery. The heartâs pumping of blood and the lungâs intake of air remind us of the plumbing in our houses. They may be complex, but they do not seem mysterious. Thoughts and emotions are different. Can we really understand them as the workings of the brain?
A journey of a thousand miles begins with a single step. To understand the brain, why not start with its cells? While a neuron may be a kind of cell, it is far more complex than any other. This is most obvious from its profuse branches. Even after many years of studying neurons, I am still thrilled by their majestic forms. Iâm reminded of the mightiest tree on earth, the California redwood. Hiking in Muir Woods, or other redwood forests on the Pacific coast of North America, is a good way to feel small. You see trees that live for centuries or even millennia, enough time to grow to vertiginous heights.
Am I overreaching to compare a neuron to the towering redwood? In absolute size, yes, but consider further how these wonders of nature stack up against each other. The redwoodâs twigs are as thin as one millimeter, a width
Itâs hopeless to answer these questions by studying only brain regions, their sizes, and their activity levels. We must look at the organization of the brain on a much finer scale. A cortical area can contain over 100 millionneurons. How are they organized to perform mental functions? In the next few chapters weâll explore this question, along with the idea that brain function depends heavily on the
connections
between neurons.
Part II: Connectionism
3. No Neuron Is an Island
The neuron is my second-favorite cell. Itâs a close runner-up to my favorite: sperm. If you have never looked into a microscope to see sperm swimming furiously, grab your favorite biologist by the lapels of his or her lab coat and demand a viewing session. Gasp at the urgency of their mission. Mourn their imminent death. Marvel at life stripped down to its bare essentials. Like a traveler with a single small suitcase, a sperm carries little. There are mitochondria, the microscopic power plants that drive the whipping motion of its tail. And there is DNA, the molecule that carries the blueprint of life. No hair, no eyes, no heart, no brainânothing extraneous comes along for the ride. Just the information, please, written in DNA with the four-letter alphabet A, C, G, and T.
If your biologist friend is still game, ask to see a neuron. Sperm impress by their unceasing motion, but a neuron takes your breath away with its beautiful shape. Like a typical cell, a neuron has a boring round part, which contains its nucleus and DNA. But this
cell body
is only a small part of the picture. From it extend long, narrow branches
that fork over and over, much like a tree. Sperm are sleek and minimalist, but neurons are baroque and ornate (see Figure 13).
Â
Â
Â
Figure 13. My favorite cells: sperm fertilizing an egg
(left)
and a neuron
(right)
Â
Even in a crowd of 100 million, a sperm swims alone. At most one will achieve its mission of fertilizing the egg. The competition is winner take all. When one sperm succeeds, the egg changes its surface, creating a barrier that prevents other sperm from entering. Whether brought together by a happy marriage or a sordid affair, sperm and egg form a monogamous couple.
No neuron is an island. Neurons are polyamorous. Each embraces thousands of others as their branches entangle like spaghetti. Neurons form a tightly interconnected network.
The sperm and the neuron symbolize two great mysteries: life and intelligence. Biologists would like to know how the spermâs precious cargo of DNA encodes half the information required for a human being. Neuroscientists would like to know how a vast network of neurons can think, feel, remember, and perceiveâin short, how the brain generates the remarkable phenomena of the mind.
The body may be extraordinary, yet the brain reigns supreme in its mystery. The heartâs pumping of blood and the lungâs intake of air remind us of the plumbing in our houses. They may be complex, but they do not seem mysterious. Thoughts and emotions are different. Can we really understand them as the workings of the brain?
A journey of a thousand miles begins with a single step. To understand the brain, why not start with its cells? While a neuron may be a kind of cell, it is far more complex than any other. This is most obvious from its profuse branches. Even after many years of studying neurons, I am still thrilled by their majestic forms. Iâm reminded of the mightiest tree on earth, the California redwood. Hiking in Muir Woods, or other redwood forests on the Pacific coast of North America, is a good way to feel small. You see trees that live for centuries or even millennia, enough time to grow to vertiginous heights.
Am I overreaching to compare a neuron to the towering redwood? In absolute size, yes, but consider further how these wonders of nature stack up against each other. The redwoodâs twigs are as thin as one millimeter, a width
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