Sam Kean

No one knows quite the reason, but surgically severing the corpus callosum can reduce the rate and intensity of seizures. So in the early 1960s, a few patients with severe epilepsy had their corpus callosums cut, turning them into split-brain people.

Brain surgery couldn't happen without the patient's own active voice to guide the work. The patient is part of the surgical team here, perhaps the most important part, and above all, that's what makes neurosurgery different.

Brains, you see, vary a lot from person to person - they vary as much as faces do.

Although it's the hub of the nervous system and the ultimate terminus of every nerve, the brain itself lacks enervation and therefore cannot feel pain.

As a child in the early 1980s, I tended to talk with things in my mouth - food, dentist's tubes, balloons that would fly away, whatever - and if no one else was around, I'd talk anyway.

Our evolution could have gone in different directions a lot of times. We could have gone extinct at some points. We might not have gotten our big brains, or Neanderthals might have made it while we did not.

I'm kind of a sucker for the retro-diagnoses.

The more that I looked at DNA, the more I realized it was nature and nurture. It's how genes and your environment work together to produce the person you are.

Genes work with probabilities; they don't work with certainties. So most things that you're looking at with these genetic tests, it's not like you're condemned to automatically get the disease or the syndrome. There's a lot of factors in play there.

Cancer is really a DNA disease... We have these certain genes that prevent our cells from growing out of control at the expense of the body. And it's a pretty good, robust system. But if a couple of these genes fail, then that's when cancer starts, and cells start growing out of control.

X-rays revealed that some people were born without a corpus callosum, and they seemed just fine.

Things look especially bleak for common killers such as diabetes and heart disease. Those ailments clearly have a genetic component. But when scientists survey genes looking for which mutations patients have in common, they come up empty.

What I find fascinating is the idea that we all have a physical brain, but we also have this mental part, and we have to figure out how they work together.

In a vague way, I always knew neurosurgery was different - more delicate, more difficult, more demanding. After all, we say things like, 'I'm no brain surgeon,' for a reason.

Medieval alchemists, despite their lust for gold, considered mercury the most potent and poetic substance in the universe. As a child, I would have agreed with them.

Everywhere in the universe, the periodic table has the same basic structure. Even if an alien civilization's table weren't plotted out in the castle-with-turrets shape we humans favor, their spiral or pyramidal or whatever-shaped periodic table would naturally pause after 118 elements.

I didn't mind staying home from school and medicating myself with vanilla ice cream and chocolate sauce. Being sick always gave me another chance to break an old-fashioned mercury thermometer, too.

Carbon's eastern neighbor on the table, nitrogen, dresses up diamonds in pinks, yellows, oranges, and brownish tints known romantically as 'champagne.'

When first presented with the jumble of the periodic table, I scanned for mercury and couldn't find it. It is there - between gold, which is also dense and soft, and thallium, which is also poisonous. But the symbol for mercury, Hg, consists of two letters that don't even appear in its name.

All human beings are, in fact, born with dozens of mutations their parents lacked, and a few of those mutations could well be lethal if we didn't have two copies of every gene, so one can pick up the slack if the other malfunctions.

In 'The Violinist's Thumb,' I talk about the poignancy of cells leaking across the placenta into both the mother and the child.

The density of space junk peaks around 620 miles up, in the middle of so-called low-Earth orbit. That's bad, because many weather, scientific, and reconnaissance satellites circle in various low-Earth orbits.

Genes are like the story, and DNA is the language that the story is written in.

Those of us raised in modern cities tend to notice horizontal and vertical lines more quickly than lines at other orientations. In contrast, people raised in nomadic tribes do a better job noticing lines skewed at intermediate angles, since Mother Nature tends to work with a wider array of lines than most architects.

Most organisms have loads of junk DNA - less pejoratively, noncoding DNA - cluttering their cells.

The humped bladderwort has yellow, snapdragon-like flowers, and it's actually carnivorous, capable of trapping and eating not just insects but even tadpoles and tiny fish.

The hippocampus helps record both types of memories initially, and it helps retain them for the medium term. The hippocampus also helps us access old personal memories in long-term storage in other parts of the brain.

Without a functioning hippocampus, names, dates, and other information falls straight through the mind like a sieve.

We really should be grateful to the people who participate in research and allow certain details to be published about themselves. Because if they didn't, we wouldn't have nearly the understanding of the brain that we do.

I think it's a natural human tendency, when you read something, you tend to read a lot of your prejudices into it. And neuroscience is like a lot of disciplines - it has fashions; things change.

A long iron rod rocketed straight through the very forefront of Phineas Gage's brain. It's kind of an unusual part of the brain: you can suffer pretty severe injuries to it and often walk away from the injury. It's not a part of the brain that's necessarily vital for your biological self. But it is very important for personality.

We human beings are humane in part because we can look beyond our biology.

DNA is a 'thing' - a chemical that sticks to your fingers.

I was reading this story about these people who suffered from brain injuries, and then their behavior changed kind of drastically afterward, and I just said to myself, 'There's no way that that can possibly be true.'

To be sure, ASPM isn't the gene responsible for building big brains - there's no such single gene. But it's critical to the process, and the primate line has almost certainly benefited from distinct changes in ASPM.

If stem cells divide equally, so both daughter cells look more or less the same, each one becomes another stem cell. If the split is unequal, neurons form prematurely.

Microchimeric sharing means that, even if the mother loses a child, she'll have a small memento of him or her secreted away inside her. Similarly, a bit of our mothers live on in all of us no matter how long ago Mom died.

Most people, even most doctors, learn that the placenta is a nice, tight seal that prevents anything in the mother's body from invading the fetus, and vice-versa. That's mostly true. But the placenta doesn't seal off the baby perfectly, and every so often, something slips across.

The amygdala is indeed crucial for monitoring our environment and deciding what's worth getting worked up over. Once the amygdala determines this, however, it merely trips another circuit to actually produce the panic.

The amygdala is one of those brain structures that a lot of people know a little bit about, and there's a definite tendency to conflate the amygdala and the fear response itself - as if the amygdala, and the amygdala alone, 'causes' fear.

Despite what you might guess, when monitoring your breathing, your body doesn't care whether you're inhaling enough oxygen. It cares only whether you're expelling enough carbon dioxide - that's the gas that sets off the panic button when you're suffocating.

The amygdala plays a crucial role in processing fear, and minus her two amygdalae, S.M. became unflappable. Studies of her are actually a hoot to read, since they basically consist of scientists concocting ever-more-elaborate ways of trying to scare her.

Animal vision - including human vision - is so biased toward movement that we don't technically see stationary objects at all.

Guinea pigs are practically synonymous with experiments. Lab rats have become the workhorses of modern medicine. Genetics owes a huge debt to the humble fruit fly. There's almost no branch of the life sciences, in fact, that hasn't leaned heavily on one animal or another.

The idea of critical windows extends beyond just vision, of course: almost every system in the brain has a critical window when it needs to experience certain stimuli, or it won't get wired up properly. The most obvious example is language: if you don't learn a language early on, it's nigh impossible to become truly fluent.

The brain, which is plastic when young, must be exposed to certain sights early in life, or it will remain blind to those sights forever.

Even fictional characters sometimes receive unwarranted medical opinions. Doctors have diagnosed Ebenezer Scrooge with OCD, Sherlock Holmes with autism, and Darth Vader with borderline personality disorder.

Despite its obscurity, probably no element on the periodic table has as colorful a history as antimony. Money, madness, poison, linguistics, charlatanism, sex - pretty much every theme that runs through the periodic table can be found in Element 51.