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In Livewired: The Inside Story of the Ever-Changing Brain, by David Eagleman makes the case that our brains and our identities are not fixed, but are continually shaped by the world around us. He argues that the brain is not a static, hardwired organ, but rather a dynamic, flexible system that constantly rewires itself based on experience. The brain adapts to changes in the body, to new sensory inputs, and to relevance and rewards in the environment. This "livewiring" allows the brain to optimize itself to best interpret incoming data and control available outputs. The principles of neural plasticity and rewiring underlie phenomena like sensory substitution devices for the blind and direct brain control of robotic limbs.
On the brain's flexibility and ability to adapt
"Dropping into the world with a half-baked brain has proven a winning strategy for humans. We have outcompeted every species on the planet: covering the landmass, conquering the seas, and bounding onto the moon. We have tripled our life spans. We compose symphonies, erect skyscrapers, and measure with ever-increasing precision the details of our own brains. None of those enterprises were genetically encoded."
On the brain constantly seeking information
“Consider phototropism in plants: the act of capturing maximum light by adopting new positions. If you watch a plant growing in fast motion, you will see that it doesn’t grow straight toward the light source; instead, it overshoots its trajectory by a little bit, then undershoots by a bit, and so on. Instead of a preplanned mission, it’s a spastic dance with constant correction.
“A similar strategy is found in the movement of bacteria. When they are searching for the center of a food source—say, a bit of sugar that has fallen on the kitchen counter—they make their way to the sugar by employing three elegantly simple rules:
1. Randomly select a direction and move in a straight line. 2. If things are getting better, keep going. 3. If things are getting worse, randomly change directions by tumbling.
“In other words, the strategy is to lock down the approach when conditions are improving and dump it when it’s not working. By this simple policy, a bacterium can quickly and efficiently work its way to the densest point of the food source.
“I propose there’s a similar principle at work in the brain. Instead of working its way toward maximizing sunlight or food, it works toward maximizing information. I call this strategy infotropism. This hypothesis suggests that neural circuitry constantly shifts to maximize the amount of information it can extract from the environment.”
On the rapidity of brain changes
"Recent decades have yielded several revelations about brain plasticity, but perhaps the biggest surprise is its rapidity. Some years ago, researchers at McGill University put several adults who had just recently lost their sight into a brain scanner. The participants were asked to listen to sounds. Not surprisingly, the sounds caused activity in their auditory cortex. But the sounds also caused activity in their occipital cortex—activity that would not have been there even a few weeks earlier, when the participants had sight."
On neural adaptations to drugs
“Consumption of a drug changes the number of receptors for the drug in the brain—to such an extent that you can look at a brain after a person has died and determine his addictions by gauging his molecular changes. This is why people become desensitized (or tolerant) to a drug: the brain comes to predict the presence of the drug, and adapts its receptor expression so it can maintain a stable equilibrium when it receives the next hit. In a physical, literal way, the brain comes to expect the drug to be there: the biological details have calibrated themselves accordingly. Because the system now predicts a certain amount to be present, more is needed to achieve the original high.
“This recalibration is the basis of the ugly symptoms of drug withdrawal. The more the brain is adapted to the drug, the harder the fall when the drug is taken away. Withdrawal symptoms vary by drug — from sweating to shakes to depression — but they all have in common a powerful absence of something that is anticipated.”