86 billion neurons weave constellations of meaning. Our brains are much more than this mass accumulation of neuronal activity, though—rather, they’re breathing, evolving systems that learn to create sensory reality from mere information. The same organ that enables you to pick up subliminal social cues on a date allows amputees to operate robotic arms with relative ease. Neuroscientists are only just beginning to explore these remarkable capabilities of the constantly shifting human brain. Renowned writer and neuroscientist David Eagleman brings readers to the cusp of new research in the realm of brain plasticity, connecting the dots of our neural portraits and sparking an internal realization: We are much more than we think.

What were you doing this time last year? Who were you with? What were you thinking about? Your answers might reflect those of a person entirely different from who you are now. According to the author, each of us is a product of a constantly shifting brain. William James, a famed psychologist of the late 19th century, called this aspect of the evolving brain its “plasticity.” Though brain plasticity is an accurate and proven scientific fact, the author prefers a different descriptor that’s better suited to the way the brain behaves within its environment: Our brains are “livewired.” The brain isn’t playdough, a pink putty that holds shape after we mold it to our liking; rather, the brain is a house under constant reconstruction, eluding our awareness with its perpetually morphing form.

The brain’s highly flexible and incomplete shape makes it amenable to adapt to whatever environment it finds itself within. Infants don’t stumble into this world with a brain that can already make sense of its surroundings, and know the meaning of its mother’s smile or the solutions to differential equations. The brain must learn about and use the world in order to survive. Our 20,000 genes provide our 200 trillion networking neurons a canvas upon which to paint a world and an experience. This is what makes the formative years, also called the sensitive period, of infancy and early childhood so potent—the environment of your 2-year-old self influences the wellness of your 52-year-old self.

Cases in which the nurture part of the “nature vs. nurture” argument were neglected are harrowing. In 2005, police in Florida uncovered one such instance of child abuse after receiving calls from neighbors who had spotted a small girl they’d never seen before in a window of a nearby home. The girl’s name is Danielle Crockett. She was just a tiny, nearly 7-year-old child at the time she was found, covered in her own excrement and bugs, locked in a closet for her entire life. Danielle failed to receive adequate nutrition, love, and input during those early years, so despite her rescue, it was unfortunately too late for her brain. 

Danielle, a feral child, lives with no discernible mental disabilities but still can’t use the restroom on her own or complete seemingly simple tasks. Her brain failed to receive the necessary input during a highly crucial stage of her development. Both the external world and interactions with people are integral to the brain’s growth, and this requirement is most critical in childhood when the brain is just forming to know itself, its environment, and the body it will learn to lead.

The layout of our bodies influences the outline of our brains. The neurosurgeon Wilder Penfield uncovered this hardly realistic aspect of the brain in 1951, calling his blueprint the “homunculus” which means “little man.” Penfield found that the section of the brain in charge of receiving inputs—the somatosensory cortex—and the part of the brain in charge of dictating outputs—the motor cortex—both embodied the human body. For instance, sensations felt along the spaces of one’s leg to one’s toes were stimulated by similarly close areas in the brain. Body parts that are near each other in human anatomy trigger places in the brain that parallel their closeness.

Later (ethically dubious) experiments on Silver Spring monkeys headed by neuroscientist Edward Taub in the 1990s proved that these little mental maps weren’t formed at birth. Rather, just like the brain itself, the homunculus modifies itself based on bodily inputs. The author notes that as neurons fire, they send electrical pulses called spikes. These spikes network with 10,000 other neurons. When one neuron’s spike is followed by another neuron’s spike, a bond is forged. Soon, much like a newly-married couple, the neurons settle down together, inhabiting a similar area of the brain, and deepening their relationship through the mutual giving and receiving of neurotransmitters.

Just like our homunculus replicates the spacing of our typically standard bodies due to neuronal spikes, our homunculus also changes to reflect a less conventional body. Our neurons rush to rearrange our cranial rooms at the slightest hint of a change, to best reflect our environment and suit our senses to derive information from such. Researcher of neurology Alvaro Pascual-Leone conducted a study to chart the speed with which the brain responded to these changing inputs, blindfolding participants for 5 days in order to simulate blindness. These blindfolded people were then trained in Braille alongside a control group of people who were not blindfolded. 

It took only 5 days for the brain to respond in crucial ways. The researchers studied the brains of the blindfolded participants and saw that their occipital cortex, the section of the brain involved in sight, was actually repurposed when they touched the Braille letters. Meanwhile, those without blindfolds employed their somatosensory cortex only and were less successful at reading Braille. Due to the participants’ temporary loss of sight, the brain rewove and redeemed itself to make sense of the stimuli it received—loss sharpened what remained.

This is why blind musicians are more likely to have perfect pitch than musicians with normal sight, and why in one study, they even scored higher on a memory test. Their occipital cortex is used to enhance the senses they still have. Nothing lost is ever really lost—not to the human brain at least.

Dreams are realms of ambiguity—being chased by monsters, failing an exam, showing up to a party without clothes—science has little understanding of why we conjure these vivid depictions during the dark hours of the night. The author may have an answer, and it brings us back to the functioning of our occipital cortex. When a body part isn’t used or receives no stimuli, its space within the brain atrophies and rearranges itself to support incoming information. Here’s where dreaming might save us from dying.

A majority of human history lived in an average of twelve hours of darkness per planetary cycle. Now we have lamps, lights, and modern electricity, but before, our brains had to fight the destruction of the occipital lobe every night. The author postulates that the brain avoided the loss of its visual function through contriving those elaborate, colorful dreams of REM sleep. Neurons in the part of the brainstem called the pons activate REM sleep, locking the body into paralysis and shooting neuron spikes to the occipital cortex. Think of it as a personal, internal movie theater—one where you have no clue what film might play and no ability to stand up and walk out if it’s a bust.

To preserve one’s ability to see, the brain stages these nightly movies of electrical circuitry to the lateral geniculate nucleus. The action doesn’t happen anywhere else, either—a factor the author views as strong evidence of its particular and integral function. Similarly, the experience of REM sleep in other organisms, both “immature” and “mature” species, solidifies this fact. “Immature” organisms like humans and ferrets are birthed into an unknown world and must learn and adapt to their environments in order to survive. “Mature” animals like giraffes arrive ready to handle what their environment may throw at them. Immature animals need about 8 times more REM sleep due to what the author argues is the formability of the early brain, which must work to maintain itself. This might also be why babies spend half of their rest in REM sleep, while adults only require 10-20% of REM. Less moldability—less dreaming.

Still, we all dream to a certain extent—our brains haven’t shed the restful necessity of REM. This is true even for those who are born blind. Instead of visual information displayed within their occipital cortex, they receive other dreamlike experiences, such as that of walking through a room. Dreams may seem like odd conglomerations of your worst fears, forgotten memories, or distant hopes, but these electric medleys may serve a purpose—even if you can’t remember them.

What does the color red sound like? Or how might electromagnetic waves feel on the tips of your fingers? The answers to those questions might always be a mystery, but that doesn’t mean the brain couldn’t figure them out if given the proper equipment. The experience of a painting or the sun on our shoulders consists of electrochemical pulses that arrive at various organs that relay information to the brain. Our experiences are dictated by our genetics, which comprise the layout of our bodily senses. The author’s Potato Head hypothesis for this phenomenon states that it doesn’t matter what organ transmits the signal to the brain; the brain will always employ bodily organs to create meaning out of mere electrochemical sparks.

The neuroscientist Paul Bach-y-Rita hailed what the author terms the advent of “sensory substitution,” with his groundbreaking research. Bach-y-Rita’s experiments concluded that the brain could employ input arriving from the skin to produce something similar to sight. Contemporary developments in sensory substitution operate within the same principle: The brain’s cortex is “pluripotent,” which means that its use can manifest in many ways depending on the available resources. The contemporary Neosensory Buzz wristband employs electrochemical pulses to replicate sound through vibrations for deaf people, translating their environments and bringing them to life.

Besides this widely useful method of sensory substitution, experiments in human sensory experience also have given way to “sensory enhancement” and “sensory addition.” Both methods use the relationship between the formable brain and senses to provide more vivid or wholly novel experiences of the world. Tapping into the pliable brain unleashes a world of seemingly fictional human abilities. The biohacker Todd Huffman placed a tiny neodymium magnet beneath his skin in order to sense the magnetic waves that constantly surround us but fly below the level of our sensory perception. Huffman says that his new ability feels as if he’s tapping a bubble—a slightly frustrating occurrence when you’re trying to fry an egg on your stove.

These seemingly utopian fantasies prove that the brain is a scavenger—it takes whatever it can get to manifest an experience. Our bodies aren’t able to soak in all the electrochemical signals that stitch our lives together, but if they could, our brains would surely use them.

At three years old, Alice seemed like an ordinary little girl, but after she started experiencing seizures, her parents sought medical help. The results of a brain scan showed a terrifying realization, one that would shake even the bravest of parents: Alice was missing half her brain. Her entire right hemisphere was completely gone. Though this looked like a dire prognosis, the reality wasn’t as grim; in fact, it was scientifically enlightening. In a usual brain with two hemispheres, visual stimuli from fibers of the right half of the retina are funneled to the right hemisphere. Because Alice was missing the right half of her brain, it actually learned to welcome the information from the fibers of both the left and right parts of the retina into the left hemisphere. This was an astonishing feat of brain self-modification, upon which the author bases his hypothesis: Changes in the brain are driven by neurons’ desire for space.

In your brain, neurons aren’t speaking to each other in a cordial and cooperative manner—rather, those neurons are negotiating, fiercely and violently for neuronal territory. Neurobiologists David Hubel and Torsten Wiesel were the first to demonstrate this aspect of the brain, gaining a Nobel Prize in 1981 for their study of mammalian eyes. Another insight, this one by Rita Levi-Montalcini, garnered yet another Nobel Prize in 1986. Levi-Montalcini discovered what are now known as neurotrophins, the protein trophies that give neurons life and inspire competition. Neurotrophins give neurons a reason to fight—they’re the lifeblood of neuronal activity, and without them, neurons perish.

Additionally, the author notes that within the brain, neurons fall into one of two categories: excitatory and inhibitory. As the names suggest, excitatory neurons get their neighbors all riled up when they send messages to others, while inhibitory neurons simply shut others down. The “livewired” brain is caught in this fluctuating pendulum. Inhibitory neurons lay down deep routes, dissuading otherwise possible connections from occurring. For instance, Alice’s brain had the capability to reshape itself into a less conventional form, but this was only realized when the quieter connections in her brain were given a chance to perform, subsequently breeding axons for different connections. In a usual brain, those secret routes are overrun by the strength of other neurons. Rivalry both inhibits and instigates changes within the brain.

For Alice, previous neural tension actually fostered peace, proving that just like the rest of us, neurons need their space.

As we age, our neural circuits fall into usual routines. Just as we wear the same brands of clothes, take the same walks around our neighborhoods, and talk to the same close friends, our neurons harden into place as we age. Our brains are wired for this—using gathered information, they develop accurate predictions in order to preserve energy. Novelty usually isn’t in the picture. Though our brains do harden with time, the author argues that plasticity differs by location. One part of the brain may be more or less welcoming to change, depending upon the information it processes. For instance, if a particular kind of information is relatively predictable in your world, such as language, the part of the brain responsible for its plasticity will be more difficult to change. But that’s only half the story.

There’s so much information swirling within our world that it’s possible for a brain to maintain a high degree of plasticity despite its age. If a brain sees change as necessary and if it’s constantly exposed to foreign experiences and new ways of thinking, then it can preserve its elastic youth. In a research experiment called the Nun Study, hundreds of Catholic nuns agreed to partake in cognitive testing and a brain scan upon death. Despite their age, the nuns remained intellectually bright, attending social events and completing their chores with no mental difficulties. Brain autopsies revealed that though one-third of those nuns maintained the neural damage indicative of Alzheimer’s disease, they didn’t display any hints of mental lapse. Their brains were always at the ready, soaking in new experiences, frustrations, and life—with constant activity, their ability prolonged. Even in spite of itself, the brain prevails.

We may have a difficult time learning Mandarin as we get older, but we can still meet new people, travel to foreign places, or at least take a new route to work. Stimulating our brains with the new enables lifelong plasticity. Our brains are powerful organs steeped in a world of constantly growing information vying to assimilate into our realities. There’s so much left to discover within the dark space between our ears and the bright atmosphere of the world around us. It’s time to get started: Pick up an interesting hobby or replace an old habit with something new. It may just change your life—and your brain, too.