Nurture or Nature?

When we think of the brain, many of us imagine this elegant, fine tuned machine with electrical currents firing rapidly as our senses take in and process thousands of pieces of information. Not so much.

David Linden, who wrote The Accidental Mind, calls it a kludge (pronounced klooj). Much like the organizations that are made of diverse segments of talent and personality, a kludge is a “design that is inefficient, inelegant, and unfathomable, but nevertheless works.” Or in the words of military historian Jackson Granholm, it’s an “ill-assorted collection of poorly matching parts, forming a distressing whole.” That’s your brain.

This “kludge” is made up of billions and billions of tiny cells – either neurons (electrical signaling) or glial cells (housekeeping functions that create an optimal environment for neurons). Sprouting from the cell body are dendrites, the branches of the neuron that receive signals from other neurons. While your brain has several branching dendrites, it also has a long, thin protrusion called the axon. This is where you get information. Axons can also branch and can be remarkably long – some can run all the way from the base of the spine to the toes.

The connections are made at synapses, which passes information from the axon of one neuron to the dendrite of the next. Synapses are critical – on average, each neuron receives 5,000 synapses – and since there are 100 billion neurons per brain, you have 500 trillion connections that tell you what, when, and how to do everything.

So, what does your brain look like when you’re born? What inherent traits do you have? Not many. Keep in mind the most important thing about brain development (and size) during birth is pretty simple – the baby’s head has to get through the birth canal so it can’t be too big. So, put away the Baby Einstein CDs, you’re wasting your time.

At birth, the brain is about 400 cubic centimeters (chimpanzee size), and will continue to grow rapidly until about the age of 5. At this point the growth slows down until completing its enlargement until about age 20, where it will have grown by more than 300 percent. A lot of changes happen along the way.

“Use it or lose it.” Even though the brain grows after birth, the number of neurons don’t necessarily increase. Many die off because they’re not needed. In fact, both before and after birth, about twice as many neurons are created as ultimately end up surviving in the mature brain. Essentially, the developing brain is a battleground – the cells that are the most electrically active survive. Synapses that are not used wither away (like the synapses carrying auditory information to deaf people). A synapse can be eliminated even if it is being used to some degree if its neighbor is much more active. Strong activation of a synapse makes those in close proximity weaker and can ultimately eliminate them altogether. Malcolm Gladwell points out in What the Dog Saw, that to truly be an expert in a field you must invest at least 10,000 hours studying it. Now, that makes a strong connection!

So, what does all this mean? When you’re born, you’re pretty close to a blank slate, and then a LOT of learning takes place. The circuits are literally being built constantly. Keep in mind, all learning is a process by which new experiences are integrated with old experiences. Therefore early experiences are important, NOT because it makes a more effective circuit, but that it creates a base for subsequent learning .

So, shouldn’t we just “over expose” our children to learning experiences? No. The brain can only handle a finite amount of information. The evidence to date is that a child’s early development is like your need for vitamins: you need a minimum dose, but beyond that, taking extra won’t help. So, you can stop playing Mozart now.

How does all this affect intelligence? In the most recent studies, it would appear that genes only account for about 50 percent of it. In trials of children and young adults from middle-class or affluent families , looking at both identical and non-identical twins raised together and apart, they found the other 50 percent was determined by environmental factors. Twins raised in poverty scored lower on intelligence tests, although the middle-class subjects did not score worse than the affluent ones. In other words, for the case of general intelligence, both genes and environment contribute, but when taken to the extreme, the environment will win out.

In contrast, behavioral traits do not appear to be influenced much by genes. Food preferences are largely determined by early experience. Sense of humor is another. Identical twins raised apart tend to not find the same things funny, whereas they do share a sense of humor with their adoptive siblings.

We also now know that the environment can actually influence gene function in brain cells. Every cell in your body has, encoded in its DNA, the information to make every cell encoded in the human genome. The “housekeeping” genes are always on, while other genes are activated in only certain cell types. For example, the cells that line your stomach are not producing the proteins needed to grow hair. Other genes may also be switched on or off at certain points of development in response to particular signals. It’s all about which neurons are “firing.”

I mentioned earlier that the brain stops getting larger about the age of 20. However, your behavioral wiring is ingrained well before that. In Travis Bradberry’s book, The Personality Code, points out that personality is predominantly housed in the Right Orbitofrontal Cortex (ROC). “We tend not to see changes in personality in adulthood because the ROC has lost its malleability by that point. Personality forms like modeling clay. When we’re born, it lacks form, and takes shape as we enter adulthood (sometimes as early as the age of 12). Reaching adulthood is the equivalent of throwing your project in the kiln – that’s the shape it’s going to stay. The ROC gradually takes more and more of our thinking as it becomes hardwired. Some inclinations are reinforced and stabilized during its development, while others become increasingly difficult to access.”

Take the curious story of Phineas Gage.

In 1848, Gage, 25, was the foreman of a crew cutting a railroad bed in Cavendish, Vermont. On September 13, as he was using a tamping iron to pack explosive powder into a hole, the powder detonated. The tamping iron—43 inches long, 1.25 inches in diameter and weighing 13.25 pounds—shot skyward, penetrated Gage’s left cheek, ripped into his brain and exited through his skull, landing several dozen feet away. Astonishingly, he survived.

Gage’s initial survival would have ensured him a measure of celebrity, but his name was etched into history by observations made by John Martyn Harlow, the doctor who treated him for a few months afterward. Gage’s friends found him“no longer Gage,” Harlow wrote. The balance between his “intellectual faculties and animal propensities” seemed gone. He could not stick to plans, uttered “the grossest profanity” and showed “little deference for his fellows.” The railroad-construction company that employed him, which had thought him a model foreman, refused to take him back. His personality had changed completely.

The area of the brain the tamping iron affected – the Right Orbitofrontal Cortex.