Yet the enormous contrast between this ordinary-looking piece of meat and the complexity within it is deeply moving. It is awe-inspiring, marvelous, to realize that everything about a human being can be contained in my hands.
This brain governed a person who was alive less than a day ago. That much I’m sure of. But what else can I know about the brain that I hold? Did it come from a woman or a man? Did this person suffer from mental illness? Did this person kill him- or herself? The likelihood of that is high, given where we get these brains. But it’s also entirely possible that the brain came from an elderly woman who died of pneumonia or a young man who was killed by a gunshot wound to his chest. The person might have suffered from schizophrenia or depression, but he also might have had a clean bill of mental health. There is no way to know from looking at it with the naked eye. The brain does not reveal its secrets easily.
A whole brain is shaped somewhat like a football and is divided by a deep groove down the middle into a left and right hemisphere. Each hemisphere has four lobes: the frontal, temporal, parietal, and occipital.
As I hold this brain in my hands, I stare at the frontal lobes, the largest of the lobes. These regions of the cerebral cortex, the outer covering of the brain, determine much of our species’ conscious existence, from our perceptions of the world to our most private thoughts and imaginings. They are the parts that fascinate me the most and that preoccupy the overwhelming majority of neuroscientists.
The major regions of the human brain.
The frontal lobes—one on the left, one on the right—extend from the bottom of the forehead, right above the eyes, all the way back to the top of the skull. Like the other lobes, they’re wrapped around the more primitive parts located farther inside the brain.
I linger over the frontal cortex, the front top part of the frontal lobe, situated roughly where the hairline is. Large and full of folds and crevices, it is both the youngest and the most evolved part of the human brain. It determines who humans are—thinking, remembering, problem-solving creatures capable of judgment and informed decision-making.
The prefrontal cortex, the foremost part of the frontal cortex, sits just behind the forehead. This relatively small part of the cortex is perhaps the most crucial to our sanity because the prefrontal cortex controls what is known as executive function—the most complex cognitive tasks, such as the ability to differentiate between right and wrong, inhibit inappropriate or impulsive behavior, and predict the future consequences of things that happen in the present. Extensive research into the neuroscience of mental illness leaves little doubt that problems of the prefrontal cortex are central to mental illness. But we don’t know what kinds of problems they are, and just by looking at this brain’s frontal cortex, I certainly can’t tell.
Behind the frontal lobe, separated by a deep sulcus, or groove, I spot the parietal lobe, another large chunk of convoluted cortex. The parietal lobe coordinates sensory information sent to the brain from the rest of the body, allowing us to feel, taste, move, and touch. It places us in space, tells us where we are in relation to things around us, and where our bodies start and end. It also enables us to read and do math.
I turn the brain on its side and peek at the temporal lobe, which lies behind the temple, roughly above where the ear is. This part of the cortex is responsible for high-level auditory processing, for hearing and understanding speech. Beneath it, deep inside the brain, hidden from my eyes and surrounded by layers of cortical tissue, sits the hippocampus, named from the Greek word for “seahorse” because of its unusual curved shape. An evolutionarily primitive part of the brain, the hippocampus stores long-term memories. It also works like a GPS, enabling spatial navigation so we know where we are.
Hidden at the back of the brain is the exquisitely ribbed cerebellum, made of densely packed neurons. It coordinates voluntary movements: how we sit, walk, and speak. Just above it, where one would tie a ponytail, is the fourth and final lobe, the occipital lobe, the structure that processes information from the eyes and enables us to see.
All of the brain structures are enormously important to everyday functioning. If you injure the brain stem at the back of your brain—the part that regulates breathing, heart rate, and other basic functions—you could be paralyzed, or die. But the frontal cortex is perhaps the most precious brain region of all. While a person won’t die without a frontal cortex, it is the part that makes us human. Damage to this region of the brain results in a large number of adverse symptoms, from memory loss to the inability to plan and organize actions, from problems with language and speaking to inappropriate behavior and poor judgment.
I would be happy to linger longer in admiration of this brain, the first I’ve ever held, but Dr. Herman and I must work quickly to preserve the specimens for our studies.
I carefully place the brain on a large board that sits atop a bed of ice and pick up the dissecting knife, which is very long with a razor-sharp edge.
“Pretend you’re slicing bread or steak,” Dr. Herman instructs me. “Keep the knife’s edge perpendicular to the top surface of the brain, and try to make each cut parallel to the previous one.”
Holding the brain with my left hand, I lift the knife and then begin to slice. The cold storage has made the tissue firm, and the knife slides
