Quickhoney for Reader's Digest
Every human being enters the world with a remarkably unfinished brain. Dolphins are born swimming; giraffes learn to stand within hours. But we humans? We’re helpless for years.
However, this seeming limitation actually signals our greatest advantage. Baby animals develop quickly because their brains wire up according to a preprogrammed routine. But that preparedness trades off with flexibility. Imagine if some hapless rhinoceros found itself on the Arctic tundra or on top of a mountain in the Himalayas or in the middle of urban Tokyo. It would have no capacity to adapt—or thrive.
In contrast, humans have thrived in all these environments. Instead of arriving with everything hardwired, a human brain is shaped by life experience. It’s “livewired.”
Our brains’ flexibility derives not from the growth of new cells but from how those cells are connected. A baby’s neurons form two million new connections every second as they take in information. By age two, a child has over 100 trillion synapses—double the number an adult has.
This peak represents far more connections than the brain will need. The incredible blooming is then supplanted by neural “pruning.” As you mature through the teen years and into your 20s, 50 percent of your synapses will be pared back.
Which synapses stay, and which go? When a synapse successfully participates in a circuit, it is strengthened; synapses that aren’t used are weakened and eventually eliminated. Just as with paths in a forest, you lose the connections that you don’t use.
By age 25, our brains appear to be fully developed. But even in adulthood, the brain can form new connections. London’s cabdrivers show just how impressive this can be. They undergo intensive training to pass the “Knowledge of London,” a memorization test of London’s extensive roadways: 320 routes, 25,000 individual streets, and 20,000 landmarks. A group of neuroscientists from University College London scanned the brains of several cabdrivers. Each driver’s posterior hippocampus— an area vital for memory, in particular spatial memory—had grown physically larger than the hippocampi of the control group. The longer a cabbie had been doing the job, the bigger the change.
Similarly, everything you’ve experienced thus far has altered the physical structure of your brain. 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. As you age, too, your brain’s flexibility, and what you choose to expose it to, matters deeply.
This was revealed by the Religious Orders Study, a research project following more than 1,100 clergy members across the United States. Since 1994, this group has undergone regular psychological and medical tests. So far, David Bennett, MD, and his team at Rush University in Chicago have collected and examined tissue from over 350 brains.
The team expected to find a clear-cut link between cognitive decline and the three most common causes of dementia: Alzheimer’s, stroke, and Parkinson’s. Instead, here’s what they found: Some people were dying with a full-blown Alzheimer’s pathology—brain tissue ravaged by the disease—without having cognitive loss. What was going on?
The team went back to its data for clues. Dr. Bennett found that cognitive exercise (keeping the brain active through doing crosswords, reading, driving, learning new skills, and having responsibilities) was protective. So were social activity, social networks, and physical activity.
The participants with diseased neural tissue but no cognitive symptoms had built up what is known as cognitive reserve. As areas degenerated, other well-exercised areas took over those functions. The study demonstrates that it’s possible to protect our brains and slow the aging process.
We’re at an unprecedented moment in history, one in which brain science and technology are coevolving. We can now hack our own hardware, and as a result, our brains don’t need to remain as we’ve inherited them. We’re now just discovering the tools to shape our own destiny. Who we become is up to us.