The Brain: The Story of You

by David Eagleman

As many as two million new connections, or synapses, are formed every second in an infant’s brain. By age two, a child has over one hundred trillion synapses, double the number an adult has.

You become who you are not because of what grows in your brain, but because of what is removed.

The shape of the hills and valleys in the brain is largely conserved across people – but the finer details give a personal and unique reflection of where you’ve been and who you are now. Although most of the changes are too small to detect with the naked eye, everything you’ve experienced has altered the physical structure of your brain – from the expression of genes to the positions of molecules to the architecture of neurons. Your family of origin, your culture, your friends, your work, every movie you’ve watched, every conversation you’ve had – these have all left their footprints in your nervous system. These indelible, microscopic impressions accumulate to make you who you are, and to constrain who you can become.

You can’t help but have your present color your past. So a single event may be perceived somewhat differently by you at different stages in your life.

So not only was it possible to implant false new memories in the brain, but people embraced and embellished them, unknowingly weaving fantasy into the fabric of their identity.

Our past is not a faithful record. Instead it’s a reconstruction, and sometimes it can border on mythology. When we review our life memories, we should do so with the awareness that not all the details are accurate. Some came from stories that people told us about ourselves; others were filled in with what we thought must have happened. So if your answer to who you are is based simply on your memories, that makes your identity something of a strange, ongoing, mutable narrative.

When the team began their research, they expected to find a clear-cut link between cognitive decline and the three diseases that are the most common causes of dementia: Alzheimer’s, stroke and Parkinson’s. Instead, here’s what they found: having brain tissue that was being riddled with the ravages of Alzheimer’s disease didn’t necessarily mean a person would experience cognitive problems. Some people were dying with a full-blown Alzheimer’s pathology without having cognitive loss. What was going on? The team went back to their substantial data sets for clues. Bennett found that psychological and experiential factors determined whether there was loss of cognition. Specifically, cognitive exercise – that is, activity that keeps the brain active, like crosswords, reading, driving, learning new skills, and having responsibilities – was protective. So were social activity, social networks and interactions, and physical activity. On the flip side, they found that negative psychological factors like loneliness, anxiety, depression, and proneness to psychological distress were related to more rapid cognitive decline. Positive traits like conscientiousness, purpose in life, and keeping busy were protective.

The participants with diseased neural tissue – but no cognitive symptoms – have built up what is known as “cognitive reserve”. As areas of brain tissue have degenerated, other areas have been well exercised, and therefore have compensated or taken over those functions.

The more we keep our brains cognitively fit – typically by challenging them with difficult and novel tasks, including social interaction – the more the neural ne...

even if many pathways degenerate because of disease, the brain can retrieve other solutions.

We can’t stop the process of aging, but by practicing all the skills in our cognitive toolbox, we may be able to slow it down.

The idea of an immaterial soul is easy to imagine; however, it’s difficult to reconcile with neuroscientific evidence. Descartes never got to wander a neurology ward. If he had, he would have seen that when brains change, people’s personalities change. Some kinds of brain damage make people depressed. Other changes make them manic. Others adjust a person’s religiosity, sense of humor, or appetite for gambling. Others make a person indecisive, delusional, or aggressive. Hence the difficulty in the framework that the mental is separable from the physical.

You don’t perceive objects as they are. You perceive them as you are.

Everything you experience – every sight, sound, smell – rather than being a direct experience, is an electrochemical rendition in a dark theater.

But presumably, every creature assumes its slice of reality to be the entire objective world. Why would we ever stop to imagine there’s something beyond what we can perceive?

Consciousness gets involved when the unexpected happens, when we need to work out what to do next. Although the brain tries to tick along as long as possible on autopilot, it’s not always possible in a world that throws curveballs.

Most situations involve too many details to reach a decision purely through logic. To guide the process, we need abridged summaries: “I’m safe here” or “I’m in danger here.” The physiological state of the body maintains a constant two-way dialog with the brain.

But there’s a twist that often gets in the way of good decision making: options right in front of us tend to be valued higher than those we merely simulate.

The thing that trips up good decision making about the future is the present.

The key to the Ulysses contract is recognizing that we are different people in different contexts. To make better decisions, it’s important not only to know yourself but all of your selves.

self-control requires energy, which means we have less energy available for the next thing we need to do. And that’s why resisting temptation, making hard decisions, or taking initiative all seem to draw from the same well of energy. So willpower isn’t something that we just exercise – it’s something we deplete.