The Brain. David Eagleman

1966, to increase the population and the work force, Romanian president Nicolae Ceauşescu banned contraception and abortion. State gynecologists known as “menstrual police” examined women of childbearing age to ensure they were producing enough offspring. A “celibacy tax” was levied on families who had fewer than five children. The birth rate skyrocketed.

      Many poor families couldn’t afford to care for their children – and so they gave them over to state-run institutions. In turn, the state rolled out more institutions to meet the soaring numbers. By 1989, when Ceausescu was ousted, 170,000 abandoned children resided in institutions.

      Scientists soon revealed the consequences of an institutional upbringing on brain development. And those studies influenced government policy. Over the years, most of the Romanian orphans have been returned to their parents or removed to government foster care. By 2005, Romania made it illegal for children to be institutionalized before the age of two, unless severely disabled.

      Millions of orphans still live in institutionalized government care around the world. Given the necessity of a nurturing environment for an infant’s developing brain, it is imperative that governments find ways to get the children into conditions that allow proper brain development.

      Without an environment with emotional care and cognitive stimulation, the human brain cannot develop normally.

      Encouragingly, Nelson’s study also revealed an important flipside: the brain can often recover, to varying degrees, once the children are removed to a safe and loving environment. The younger a child is removed, the better his recovery. Children removed to foster homes before the age of two generally recovered well. After two, they made improvements – but depending on the age of the child they were left with differing levels of developmental problems.

      Nelson’s results highlight the critical role of a loving, nurturing environment for a developing child’s brain. And this illustrates the profound importance of the environment around us in shaping who we become. We are exquisitely sensitive to our surroundings. Because of the wire-on-the-fly strategy of the human brain, who we are depends heavily on where we’ve been.

       The teen years

      Only a couple of decades ago it was thought that brain development was mostly complete by the end of childhood. But we now know that the process of building a human brain takes up to twenty-five years. The teen years are a period of such important neural reorganization and change that it dramatically affects who we seem to be. Hormones coursing around our bodies cause obvious physical changes as we take on the appearance of adults – but out of sight our brains are undergoing equally monumental changes. These changes profoundly color how we behave and react to the world around us.

      One of these changes has to do with an emerging sense of self – and with it, self-consciousness.

      To get a sense of the teen brain at work, we ran a simple experiment. With the help of my graduate student Ricky Savjani, we asked volunteers to sit on a stool in a shop window display. We then pulled back the curtain to expose the volunteer looking out on the world – to be gawked at by passersby.

       Volunteers sat in a shop window, to be stared at by passersby. Teenagers have greater social anxiety than adults, reflecting the details of brain development during the adolescent years.

      Before sending them into this socially awkward situation, we rigged up each volunteer so we’d be able to measure their emotional response. We hooked them up with a device to measure the galvanic skin response (GSR), a useful proxy for anxiety: the more your sweat glands open, the higher your skin conductance will be. (This is, by the way, the same technology used in a lie detector, or polygraph test.)

      Both adults and teens participated in our experiment. In adults, we observed a stress response from being stared at by strangers, exactly as expected. But in teenagers, that same experience caused social emotions to go into overdrive: the teens were much more anxious – some to the point of trembling – while they were being watched.

      Why the difference between the adults and teens? The answer involves an area of the brain called the medial prefrontal cortex (mPFC). This region becomes active when you think about your self – and especially the emotional significance of a situation to your self. Dr. Leah Somerville and her colleagues at Harvard University found that as one grows from childhood to adolescence, the mPFC becomes more active in social situations, peaking at around fifteen years old. At this point, social situations carry a lot of emotional weight, resulting in a self-conscious stress response of high intensity. That is, in adolescence, thinking about one’s self – so-called “self evaluation” – is a high priority. In contrast, an adult brain has grown accustomed to a sense of self – like having broken in a new pair of shoes – and as a result an adult doesn’t care as much about sitting in the shop window.

       SCULPTING OF THE ADOLESCENT BRAIN

      After childhood, just before the onset of puberty, there is a second period of overproduction: the prefrontal cortex sprouts new cells and new connections (synapses), thereby creating new pathways for molding. This excess is followed by approximately a decade of pruning: all through our teenage years, weaker connections are trimmed back while stronger connections are reinforced. As a result of this thinning out, the volume of the prefrontal cortex reduces by about 1% per year during the teenage years. The shaping of circuits during the teen years sets us up for the lessons we learn on our paths to becoming adults.

      Because these massive changes take place in brain areas required for higher reasoning and the control of urges, adolescence is a time of steep cognitive change. The dorsolateral prefrontal cortex, important for controlling impulses, is among the most belated regions to mature, not reaching its adult state until the early twenties. Well before neuroscientists worked out the details, car insurance companies noticed the consequences of incomplete brain maturation – and they accordingly charge more for teen drivers. Likewise, the criminal justice system has long held this intuition, and thus juveniles are treated differently than adults.

      Beyond social awkwardness and emotional hypersensitivity, the teen brain is set up to take risks. Whether it’s driving fast or sexting naked photos, risky behaviors are more tempting to the teen brain than to the adult brain. Much of that has to do with the way we respond to rewards and incentives. As we move from childhood into adolescence, the brain shows an increasing response to rewards in areas related to pleasure seeking (one such area is called the nucleus accumbens). In teens, the activity here is as high as it is in adults. But here’s the important fact: activity in the orbitofrontal cortex – involved in executive decision making, attention, and simulating future consequences – is still about the same in teens as it is in children. A mature pleasure-seeking system coupled with an immature orbitofrontal cortex means that teens are not only emotionally hypersensitive, but also less able to control their emotions than adults.

      Moreover, Somerville and her team have an idea why peer pressure strongly compels behavior in teens: areas involved in social considerations (such as the mPFC) are more strongly coupled to other brain regions that translate motivations into actions (the striatum and its network of connections). This, they suggest, might explain why teens are more likely to take risks when their friends are around.

       Due to changes in many brain areas involved in reward, planning, and motivation, our sense of self undergoes major changes in our teenage years.

      How we see the world as a teenager is the consequence of a changing brain that’s right on schedule. These changes lead us to be more self-conscious, more risk-taking, and more prone to peer-motivated behavior. For frustrated parents the world over, there’s an important message: who we are as a teenager is not simply the result of a choice or an attitude; it is the product of a period of intense and inevitable neural change.