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What do we know about the brain that our grandparents did not? A hundred years ago we thought the brain was this undifferentiated gelatinous mass of stuff. We used to get our ideas about what parts did what by looking at strokes, gunshot wounds, brain tumors-the eliminated parts. It was useful but crude, like trying to understand how a computer works by putting a bullet through different parts of your PC.
How do we gain our better understanding today? I can put you into a scanner and see what parts of your brain are functionally active. For instance, I can see what brain areas are overactive when a schizophrenic is hallucinating. We can map the parts of brain involved in fear and courage when you’re arachnophobic and you see a spider approaching. When you listen to Mozart versus Shostakovich. We can now examine not only which parts are active, but what’s wired to what-the connectivity. Your brain isn’t just a series of spots of activity, it’s like a society. There are 100 billion neurons, yet each neuron communicates with only about 10,000 others. Not so different from our society, really-six billion people, but on average we each only have about 150 friends. As your brain grows, these neurons are refining and sculpting their connections. The brain cells are in competition at the same time that they’re cooperating with each other. And now we have the ability to see that connectivity in real time, in living people.
What has the Human Genome Project taught us about the brain? A gene is just a piece of DNA that’s going to make a protein some day. The Human Genome has found there are about 20,000 human genes. Fewer than we thought-we have about the same number as rice does, though we may be smarter at organizing them. Probably two-thirds of those 20,000 genes are used to either grow your brain or operate it. So it takes more genetic horsepower to make and run your brain than to make all the rest of your body combined. I joke with my geneticist friends, “You’re working for us now.” Most of genetics, it turns out, is really neuroscience.
Even genetic illness? Molecular neurobiology is a huge revolution. Mutations and/or minor alterations in brain genes either directly cause or predispose to all kinds of diseases. Some minor variations strongly increase the risk of Alzheimer’s. Mutations in other genes predispose to Parkinson’s. There was an interesting study led out of Toronto recently in which they did gene sequencing on autistic children and they identified several dozen mutations that lead to autism.
And what about brain injury from physical trauma? Concussions have become rampant in sports. It’s true, we’re seeing an epidemic of neurotrauma, and not just in sports. It’s also become the signature war injury. Over 20 percent of soldiers who return from Iraq or Afghanistan have had some sort of brain injury. There are short-term consequences of these injuries, and luckily battlefield surgery has improved dramatically so more lives are saved. But the evidence has become quite overwhelming that brain damage predisposes you to later dementia. People who’ve had a stroke, or who have been concussed-their chances of developing Alzheimer’s roughly double.
Norman Doidge’s book, The Brain That Changes Itself, recounts remarkable tales of neuroplasticity. Can you really change the composition of your brain with exercise, physiotherapy, positive thinking? If you remember this conversation, it will be because of changes in your brain. Your brain is constantly changing. I’ve actually done a lot of work in neuroplasticity myself-my work has focused on the neuroplasticity of early life. We found that if you don’t use one of your eyes early in life, say I put a patch over it for as little as a few days, it will be outcompeted by the other eye. If the two eyes begin to send dissimilar information, or one sends useless information, the stronger eye stakes out more cortical territory at the expense of the other. Use it or lose it-that’s neuroplasticity. Another classic example is Henry Kissinger and his brother. Henry arrived in the States when he was 11 and his brother was eight. The brother speaks perfect, unaccented English. Henry does not. There you have the age dependence of language plasticity.
When an Arizona congresswoman gets shot through the head, is her 40-year-old brain likely to adapt and accommodate? It’s on the left side, and that’s not good: if you’re right-handed, the left side of your brain has the speech areas and tends to be the dominant hemisphere. I don’t know the exact trajectory of the bullet, but if it went through the parts of Gabrielle Giffords’s brain involved in understanding speech or articulation, she may not be able to understand, may not be able to speak-it all depends. If the bullet went through the back of her head, she may have visual difficulties. If it went through her frontal lobe, she may have personality changes, become impulsive, find it difficult to plan ahead.
And can the brain be regenerated at her age? She was apparently very smart and articulate. It may be that she had good plasticity to start with, and that’s what got her to where she was. But a big reorganization is required. Functions have to be replaced, reallocated. After an injury, the brain goes through a period when a lot of synaptic space is created. In this sense, in disaster there is opportunity. The rehabilitation process she’s involved in now is going to push the limits of her brain plasticity. But generally, the adult brain is not great at regenerating itself.
Is that why old people tend to forget things? In general, yes, memory gets worse because neuroplasticity declines. Old brains make fewer new brain cells. The part of your brain that makes new cells-the hippocampus-shrinks by about five percent each decade after you turn 40. Working out at the gym helps with that and so does cognitive stimulation, leading an active, interesting life-that’s why I plan on being carried out of this office in a box.
What role does diet play? Diet is important, obviously. Your brain weighs just 1.3 kilograms, yet it consumes a quarter of your blood supply and of your body’s glucose. It also contains the highest concentration of fats of any organ in the body. So keep eating those fatty fish, like salmon.
Do herbs like ginkgo biloba and ginseng improve mental functioning? There’s no scientific evidence that they do. I ate my blueberries last night, but I don’t favour the view that there’s magic food for the brain. What you want is a balanced, healthy diet. You want to preserve your circulation, keep your cardiovascular system in good shape. So stay fit. Eat foods of different colours-put a rainbow on your plate. And eat less. There’s a lot of evidence that eating less is good for the system. It cleans out the body. Eating less also biochemically affects the brain in a way that improves longevity.
What the heck, let’s go have a nice dinner. Who wants to live to 90? People who are 89!