چهارشنبه 23 فروردین 1391
Genes and environment don’t explain everything. We’re wired by experience.
Published on April 10, 2012 by Loretta Graziano Breuning, Ph.D. in Your Neurochemical Self
People debate nature vs. nurture as if they add up to 100%. Genes and environment don't explain everything. A huge chunk of what you are comes from the neural network you built from experience.
You were not born with a circuit chip in your brain, and you were not programmed by your culture. You built your neural circuits one connection at a time. Even the essential connections between your limbic system and your cortex, the pathways that tell your happy chemicals when to turn on and off, built up from experience. Instead of being born to love acorns and fear coyotes like a squirrel is, you were born to love and fear based on your past experience of pleasure and pain
Of course, your experience is shaped by your environment and your genes. But there's more to it. Your experience is shaped by the experiences that came before. Your neurons start making connections as soon as you're born, and strong experiences of pleasure and pain shape the way you see the world. As you start choosing your experiences, you keep weaving the neural tapestry that you've become. Before you presume genes and culture explain everything, consider these unique individual tapestries.Churchill’s father called him a loser and his mother barely noticed him. Blame their genes and the British aristocratic culture if you want. But first, consider the neural connections triggered by these experiences.
Winston’s grandfather called Winston’s Dad a loser, so it’s not surprising that Dad went on to disdain his son. Getting put down as a child activates a neurochemical submission response. It’s easy to see this in monkeys when they dominate and submit. Serotonin rises in the monkey that dominates and falls in the monkey that submits. When a young child is dominated by family members, the brain learns to produce a submission response quickly and efficiently. The young brain doesn’t care whether the dominator is weak or poor in the outside world or the Duke of Marlborough (Winston’s grandfather). What matters is that experience builds connections that channel future experience.
Churchill’s Mom was the New York socialite Jennie Jerome, whose father built Jerome Avenue in the Bronx. She was too busy making social conquests to form a reliable attachment to Winston. Without that secure attachment, Winston missed opportunities to build trust circuits that could stimulate his oxytocin in the future. When he grew up, Jennie helped him by asking favors of her prominent lovers. Winston learned from this because we all learn from behaviors that get rewarded. No, he didn’t learn to be promiscuous (not surprising since he watched his father die of syphilis). Young Winston learned to ask favors of prominent people.
Our mirror neurons fire when we watch others seek rewards and avoid pain. This wires us to learn from the behavior of others. Churchill learned different behaviors from each parent, as we all do. From his father, he learned to feel bitter and rejected. From his mother, he learned to be a risk-taking social conquistador. In the end, he was wired for depression but also for damning the torpedos and speeding ahead. You can chalk it up to torpedo-damning genes or a torpedo-damning environment. But you can also see how he got wired by experience.
Carl Jung’s struggle with psychosis
Jung talked to spirits. His mother did too, and she brought Carl into her conversations with the spirit world when he was very young. You can say they both had genes for psychosis, or that they were both products of a spiritual culture. But there’s a simpler explanation: children learn from experience. If your mother talks to the dead, your mirror neurons fire and wire you to do the same.
To a kid, all experience is real. I heard of elephants when I was young and I came to believe they are real though I never touched one. Carl Jung came to believed in ghosts in the same way. The spirit world was as real to him as elephants were to me. Young brains don’t filter experience because they lack neural pathways to filter with. Over time, your brain focuses on things that help meet your survival needs. For Jung, talk of the supernatural brought him fame and fortune, so he had good reason to keep focusing on the supernatural.
My family’s struggle with obesity
Most of my relatives were obese, but my brothers and I are not. Genes? Environment? Before you generalize, consider these individual strands of experience.
My mother grew up hungry. She literally didn’t know where her next meal was coming from sometimes. Her brain learned that food may not be there when you need it, so you better grab it when you can. Immediate survival needs get your brain’s attention and build links that shape how you see the world.
I experienced hunger in a different way. I was born at a time when parents were advised to feed their babies every four hours, and to stick to the schedule no matter how heart-breaking the baby’s cries. When a baby is hungry, their brain perceives it as a survival emergency because low blood sugar triggers cortisol. When a baby is fed, it learns to expect that its needs will be met. We start building expectations about the world from the first moments of life.
Early wiring is most amenable to change during puberty, because hormones help pave new neural pathways. When my mother was in puberty, she saw her father steal the family’s food money. Her hunger was thus compounded by anger. The normal hunger we feel once our last meal has digested felt like an emergency to my mother. Passing up a cookie triggered the sense of extreme deprivation she had built from experience. When I was a teenager, I learned from different experiences. I could see that obesity has social consequences.
My father was skinny when he met my mother. His father left Sicily at age fourteen with his sixteen year-old brother. They went to New York in 1910 because their parents couldn’t feed them. In their culture, a “family style” meal meant that everyone watched what you took from the platter because no one ever had enough to eat. That culture evolved into the “Mangia! Mangia!” image we have today because the chance to eat your fill was such a rare treat in the experience of our ancestors.
My father started eating when he married my mother. It would be polite to say the joy of her cooking was the cause. But I will tell the truth since my parents have passed on and the truth can help others. Our meals were often spiced by my mother’s temper tantrums. Emotional eating was on the menu. When my mother started screaming, I wanted to shovel food into my face to distract myself. I eventually learned not to do that by shifting my attention toward dreams for a life elsewhere – a life that would be harder if I was obese.
Survival experiences build layers of neural circuitry. I love to read biographies because I see the threads of experience weaving over time. It’s foolish to presuppose that genes and culture explain everything when it’s so obvious that early experience builds the brain.
Why do “experts” reduce everything to nature and nurture and skim over the huge impact of early experience? I will answer this question next week. Look out for Part 2 of Don’t reduce everything to nature and nurture.