You must have read our informative article about General Artificial Intelligence in my previous message. Now, let's delve into the topic from a broader perspective: how does the brain shape itself, are all brains structurally the same, and what happens in the brain as we grow? Let's take a closer look at all these questions. This week, my guide will be David Eagleman's book, "The Brain." I've quoted relevant sections from this book. I wish you enjoyable reading
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Although neuroscience is a part of my everyday life, I find myself staring in awe whenever I hold a human brain in my hands. Let's set aside its considerable weight (an adult human brain weighs around 1.5 kilograms), its strange, jelly-like consistency, and its convoluted surface divided by deep fissures; the remarkable aspect of the brain is its physical presence itself. This seemingly ordinary mass of matter creates such a contrast with the mental processes it generates...
All our thoughts and dreams, memories and experiences stem from this peculiar neural tissue. Our identity is hidden within the brain's intricate electrochemical firing patterns. The cessation of these activities means our end as well. The alteration of activities, whether due to damage or medication, implies an alteration in our character without skipping a beat. Unlike in other parts of the body, the development of minor damage in the brain can lead to fundamental changes in your personality. To understand how this is possible, let's start from the beginning.
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We humans are born entirely helpless. It takes about a year to walk, roughly two years to articulate formed thoughts, and many more years to become self-reliant. We are entirely dependent on the people around us to survive. Now let's look at the situation that applies to most mammals. For instance, dolphins start swimming shortly after birth; young giraffes learn to stand within hours; a zebra foal can run within forty-five minutes of birth. The independence these relatives in the animal kingdom gain shortly after birth is quite striking.
At first glance, this may seem like a significant advantage for other species, but it actually points to a significant limitation. The reason for this rapid development in animal offspring is that their brains establish connections largely based on a pre-programmed template. However, the cost paid for this preparation is flexibility. Imagine an unfortunate rhinoceros suddenly finding itself in the tundra of the Arctic, on the peak of a Himalayan mountain, or in the midst of the city of Tokyo. This rhinoceros lacks the ability to adapt to the new region; and indeed, the reason rhinoceroses are not found in these regions is precisely this. The strategy of being born with a pre-programmed brain works within a specific region of the ecosystem. However, the chance of survival and development diminishes when the animal is removed from that region.
Humans, on the other hand, have the ability to live in many different environments, from icy tundras to high mountains or bustling cities. The reason for this is that we are born with brains that are remarkably underdeveloped. The human brain does not emerge with everything 'hardwired'; instead, it allows itself to be constantly reshaped by the details of life experiences. The prolonged periods of dependency are the result of this process. The young brain gradually molds itself to adapt to its surroundings during these intervals because life is not immutable but flexible.
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Many animals are born with certain instincts and behaviors genetically pre-programmed; these instincts and behaviors are engraved in their brains as patterns. Their genes instruct their bodies and brains to develop in certain ways, determining what they will become and how they will behave. The reflex of a fly to flee from passing shadows, the instinct of a robin to fly south when winter approaches, the desire of a bear to hibernate in winter, the urge of a dog to protect its owner... These are all examples of instincts and behaviors ingrained in the brain. Being pre-programmed allows these animals to act like their parents from birth and, in some cases, to survive independently by procuring their own food.
The situation is somewhat different in humans. When we come into the world, our brains have undergone a certain degree of genetic pre-programming as well. We utilize this feature when we breathe, cry, suckle, recognize faces, and acquire the ability to learn the nuances of our native language. However, humans are born with remarkably incomplete brains compared to the other members of the animal kingdom. The detailed circuitry of the human brain is not pre-programmed; instead, genes provide highly general instructions for organizing neural networks, with fine-tuning of the networks accomplished through experiences. This allows the brain to adapt to local conditions and details.
The ability of the human brain to regulate itself to suit the world into which it is born has enabled our species to dominate all ecosystems on the planet and has paved the way for the first steps into the depths of the solar system.
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What is the secret behind the flexibility of young brains? It cannot be said to be related to the formation of new cells; in fact, the number of brain cells in children and adults is the same. The secret lies in how these cells connect to each other.
The neurons of a newborn baby are quite different and unconnected from each other. In the first two years of life, neurons start to connect with each other very rapidly based on the sensory information they receive; so much so that approximately two million new connections, or synapses, are formed in the baby's brain per second. By the end of two years, the number of synapses in a baby exceeds one hundred trillion, which is twice the number of synapses in an adult.
The brain has now reached a peak and has established far more connections than it needs. At this point, the process of forming new connections gives way to another strategy called neural "pruning," where about 50% of synapses gradually prune and disappear as age progresses.
So, which synapses stay, and which ones go? A synapse that succeeds in taking its place in a brain circuit strengthens, while unused synapses weaken and eventually become inactive. Just like pathways in a forest, you lose connections that you don't use.
From this perspective, the process that defines who you are is defined by eliminating one possibility after another. What makes you who you are is actually not what develops in your brain but what is eliminated from your brain.
In a newborn brain, neurons (nerve cells) have relatively few connections. Within the first 2-3 years, branching and consequently connections between cells increase. Subsequently, connections that are gradually 'pruned' decrease in number and strengthen in the adult brain.
Throughout our childhood, the environment we are in intricately shapes our brains and reshapes the array of possibilities based on the experiences we are exposed to. Consequently, our brains form fewer but stronger connections.
For example, as a baby, your ability to perceive sounds specific to the language spoken in your environment (let's say English or Japanese) enhances, but it negatively affects your ability to perceive sounds specific to other languages. As a result, both a baby born in Japan and a baby born in the USA will respond to all sounds in both languages, but the baby raised in Japan will eventually lose the ability to distinguish sounds represented by the letters R and L; because these two sounds are indistinguishable in Japanese. In summary, we shape ourselves according to the world we live in.
We adapt to our environment, and our brains are one of the important components of this adaptation, guiding this change. Pay close attention to the environment you develop in, what you are exposed to in your daily life, what you watch, listen to, the people you spend time with, your activities, and your diet. Because all of these shape and change your brain and you.
Wishing you plenty of enriching readings!
References:
Eagleman, David. Beyin — Senin Hikayen. İstanbul: domingo, 2022.
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