Boost Your Brain (3 page)

I had started medical school with a deeper well of medical knowledge than the average student—at least when it came to brain-related matters—having taken the unusual route of completing my Ph.D. in neuroscience at Johns Hopkins University before I started medical school. I was actually in the M.D. program at Harvard by way of a teaching scholarship offered through Harvard-MIT Division of Health Sciences and Technology, which put me in the unlikely position of teaching neuroanatomy to my medical school classmates while I was a student myself. I knew neuroscience. But for medical conditions below the neck, I was in much the same position as my classmates: nervous, but also eager to learn everything I could about the human body.

So, it was with equal parts uncertainty and excitement that I greeted my obstetrics professor as she sauntered over to me in the delivery room that day. Motioning to a nineteen-year-old woman who was nearing the final stages of labor, she said, “You’ll deliver this one,” turning an ordinary day into one I will never forget.

In the delivery room, I was gowned and gloved and, I’ll admit, sweating profusely as the baby began her trip down the birth canal. A new life was entering the world and I didn’t want to mess it up. Thankfully, everything went according to plan, and after the mother-to-be gave a few final pushes, I eased the baby into my hands. Now, this is an incredible moment even after you’ve experienced it a few times, but I’ll never forget the feeling I had sitting there, amid the happy tears of the new mom and her family (and even a few of my own), holding that baby girl, who would soon be named Sara.

Nine months ago she was a microscopic bundle of rapidly dividing cells—first two, then four, then eight, sixteen, and on (into the trillions!). How could she have grown into this bawling, squirming, perfectly formed human? Along the way, a million things could have gone wrong. And yet, here she was. With eyes that one day would be able to distinguish several thousand shades of color, a complex auditory system capable of transforming vibration in the air into sound (and turning those sounds into intelligible thoughts and concepts), and a heart that would beat some hundred thousand times a day, every day.

One year later, having spent time training in the pediatrics, psychiatry, cardiology, and medicine wards, I was doing another rotation in my life as a medical student, this time in neuropathology, an elective whose choice reflected my fascination with the human brain. Neuropathology, the study of diseases of the central nervous system, involves performing autopsies to detect disease in the brain (both by examining it first with the naked eye and later under the microscope), and I was as eager to jump in as I had been on my obstetrics rotation. I was grateful, too, to finally spend weeks focused on exploring the brains of patients who had Parkinson’s disease, multiple sclerosis, head trauma, and Alzheimer’s disease. By comparing their brains to those of otherwise healthy elderly people who had died of natural causes, I knew I would gain a new understanding of the workings of the brain and how it changes with aging and disease.

Just as I had for the OB rotation, I progressed in steps, first watching someone else perform a brain autopsy, then inspecting an already-prepared brain, and finally, handling the delicate procedure of removing the brain from the skull. But unlike in obstetrics, neuropathology takes place in a morgue, a cold, sterile room—think bare walls, metal tables, and concrete floors—inevitably tucked away in the bowels of the hospital building. There’s another big difference: in neuropathology, patients don’t cry or squirm or come to harm if you make a wrong move.

Still, the brain can’t be properly studied if it’s handled roughly or, God forbid, dropped. And you only get one shot at successfully removing it from the skull.

My moment to perform a brain autopsy finally came one weekend morning with a call from the morgue. “If you want to do this one, come on in now,” the professor I was working with said. I hopped on my bicycle, pedaled to another Harvard teaching hospital, Massachusetts General Hospital, and quickly changed into hospital scrubs. Awaiting me in the basement morgue was the body of an eighty-five-year-old woman who had died of aspiration pneumonia and had suffered from dementia. Her name was Mrs. Grey.

By this point, I had seen enough cadavers and exposed brains that I was quite comfortable entering the morgue and preparing for the autopsy. Still, as I donned my protective gown, face mask, and hood, I felt a nervous anticipation that wasn’t too unlike those days in the delivery room.

To remove the brain from the skull, the coroner and I first had to cut away the top of the skull, just above the eyebrow, with the help of an electric saw. There is some delicacy needed: slice too deeply and I’d destroy the delicate grey matter within. Once the skull was cut, I set the bowl-like top piece aside and gently pulled the brain outward, making space to slice away its attachment to the spinal cord. I then eased Mrs. Grey’s brain out and let it fall gently into my cupped hands.

A brain has the consistency of Jell-O and, like a baby, it is fragile—and a little slippery. In a moment, I would weigh it, examine it visually, and then place it in a formalin-filled bucket to preserve and harden it so that it could be dissected and observed under a microscope. Even without a microscope, though, I could see the ravages of time—instead of the plump peaks and minimal valleys of a young, lush brain, Mrs. Grey’s had deep ridges separated by wide spaces.

As I cradled Mrs. Grey’s brain in my hands, I remember marveling in much the same way I had on the day Sara was born. In my hands were three pounds of cells that had powered an entire life. It was the very essence of that life: the neurons and connections that spurred Mrs. Grey to volunteer at the library on weekends, smile when she saw her grandson’s face, or get grumpy when she was stuck in traffic.

In between the moment she’d first seen those bright delivery-room lights and the moment her last neuron had fired, every experience her brain had encountered shaped the person she became. And yet, no one at the time would have suggested that how she lived her life as an adult had substantially altered the size and structure of her brain. At the time, in the mid-1990s, the human brain was widely believed to finish its development and become fixed in structure by childhood. After that, there would be only one inevitable possibility for structural change: the brain would shrink with age. That’s what everyone thought. But, as you’ll soon learn, “everyone” was undeniably wrong.

Your Brain, Baby

What happened to Mrs. Grey’s brain in those eighty-five years between birth and death? And how did changes inside her brain affect her cognitive abilities throughout life? How might she have steered those changes in one direction or another—and to what end?

Mrs. Grey’s story started the same way that Sara’s had: with a tiny clump of cells. I’ll stick with the simple version of brain development and aging, but even simplified it’s an incredible tale. Human life, after all, begins as one cell and ends with some hundred billion in the brain alone.

We can start the story of Sara’s brain by taking a peek inside her mom’s uterus at about the third week of gestation. Remember those dividing cells? At about this time, some will form a column of cells the shape of a tiny tube. At one end of the tube, cells will develop into the spinal cord, while at the other end cells will develop to form the brain’s two hemispheres. Most of these cells become neurons and at one end will have extensive branches—tens of thousands of them—called dendrites, which will act as antennae to receive input from other neurons. At its other end, each neuron will sprout a single long extension called an axon, which in turn will sprout at its tips tens of thousands of swellings called axon terminals.
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Within Sara’s brain, these neurons will begin to send messages to each other via electrical signals that “leap” from the axon terminal of one neuron to a special docking site on the dendrite of another neuron, crossing a gap called a synaptic cleft. Eventually the brain will contain more than one hundred trillion such synaptic connections.

As Sara grows in her mother’s uterus, her brain will continue to form as a sheet of cells called the cortex, which develops rapidly and extensively, so much so that it folds in on itself hundreds of times, giving the outer portion of the brain its cauliflower-like appearance. Other brain structures will develop beneath the cortex, but it is in the cortex that all of Sara’s higher cognition will take place. This is ground zero for her future memory, attention, perceptual awareness, thought, language, and ability to make decisions. Sara’s cortex in either hemisphere will further develop into five symmetrical lobes, which are recognized by landmarks on the surface of the brain and form in roughly the same place from one person to the next. Each lobe (roughly the size of an orange) will contain several billion neurons, which will exchange trillions of messages with each other, with neurons in the other hemisphere, and with deeper brain structures.

The cortex in the
frontal lobes,
just above and behind Sara’s eyes, will develop to handle planning, execution, and control of movements. In the right hemisphere, her frontal lobe will be particularly tied to art and music appreciation as well as intonation in speech. In the left, it will be tied to logical thinking, concentration, and understanding symbols in reading and writing.

Near the ears, Sara’s
temporal lobes
will develop to handle her sense of hearing and understanding language, among other things. Deep within each temporal lobe the hippocampus will form. It will be key to all aspects of memory.

Between her frontal and temporal lobes, the
parietal lobes
will develop to handle various sensory inputs from the skin. They will take charge of Sara’s sense of touch, her ability to feel weight or motion, proprioception (the sense of knowing where parts of the body are at a given time, without having to look), and self-orientation. The parietal lobe on the right will help her with navigation, while the parietal lobe on the left will deal with calculation.

At the back of her brain, the
occipital lobes
will form. They will handle vision and will be integral to recognizing a familiar face or detecting a constellation of stars at night. Sara’s occipital lobes will enable her to both see and make sense of what she sees.

Sara’s forming brain will also include a
limbic lobe,
a collection of cortical areas in the frontal and temporal lobes, plus some deeper brain structures. One is the amygdala, an almond-shaped structure (actually there are two—one in each hemisphere), which is tied to emotions. Another component of the limbic lobe is the hypothalamus, which regulates hormones involved in a person’s fight-or-flight response, eating, and metabolism, and is closely connected to the amygdala. Both the amygdala and hypothalamus are closely linked to the hippocampus.

The various parts of Sara’s cortex will communicate with each other and with a dozen deep brain structures as well as the spinal cord via nerve bundles, which act as highways within the brain.

As Sara’s brain develops, it is the conversation between neurons—those electrical signals passed and received—that keep them alive and connected. When they fire a signal across the synaptic gap, they strengthen each other, “wiring” them together and increasing their chances of survival. “Neurons that fire together, wire together,” as neuroscientists like to say.

Neurons that don’t fire and wire see their connections culled and shrivel away—which happens later in life through a phenomenon called disuse atrophy, or the “use it or lose it” principle. This process is critical during the initial stages of brain development but persists throughout life—a fact that is critical in our quest to grow the brain, as you’ll soon read.

In the weeks before she’s born, Sara’s brain will continue to rapidly develop, so that by the time she enters the world it will be about 90 percent complete. Important areas needed for survival will have developed fully in order to ensure that she breathes, sleeps, and sucks when presented with anything that resembles a nipple.

And yet, she’s ready for survival in only the most basic sense. If a predator were to walk through the delivery room door, Sara couldn’t get up and run to safety. She couldn’t yet make the decisions—to gather food, work, protect herself from the elements—that would preserve her life as an adult.

Newborn Sara couldn’t do any of these things, in part because her cerebellum—responsible for balance, coordination, and eye movement—hasn’t fully developed, and in part because the connections between the neurons elsewhere in her brain have not yet fully formed, making it impossible for messages to be smoothly passed or functions to be fully coordinated. Her brain, at this point, is a little like a city under construction. And understanding how that city is built can shed light on how it can crumble—or grow—later in life.

The Phenomenal Hippocampus

You’ll hear about the hippocampus over and over again in this book. And for good reason. The hippocampus, after all, is the gateway for new memories and essential for learning; as such, it is a major player in the quest for a bigger, stronger brain. Not only that, but the hippocampus is also the most malleable of brain regions. It is the first region to shrink with aging but also the quickest to grow in adulthood. And changes in its size bring noticeable changes in a person’s memory and cognitive function.

That’s not to say that your hippocampus works alone. The hippocampus is most instrumental in making new memories, but many other parts of your brain are also involved in creating and storing memory.

In simplistic terms, it might help to think of the hippocampus as a librarian. It processes all new information and decides what to keep and what to discard—tossing out those free advertising mailers, for example, while storing a copy of a front-page article of the
New York Times
. The good stuff—that which the hippocampus deems storage-worthy—is sent to various parts of the cortex for long-term storage. Information dubbed forgettable—like a phone number you’re repeating in your head until you’re able to type it into your phone—may be held for a short time but is then quickly tossed.