In “Welcome to Your Brain,” two neuroscientists offer interesting facts and dispel myths about the mind. An excerpt.
Why can’t you tickle yourself?When doctors examine a ticklish patient, they place the patient’s hand over theirs during the exam to prevent the tickling sensation. Why does this work? Because no matter how ticklish you may be, you can’t tickle yourself. Go ahead. Try it. The reason is that with every move you make, part of your brain is busy predicting the sensory consequences of that movement. This system keeps your senses focused on what’s happening in the world so important signals aren’t drowned out in the endless buzz of sensations caused by your own actions.
For instance, as we write, we are unaware of the feel of the chair and the texture of our socks. Yet we’d immediately notice a tap on the shoulder. If the only information your brain received was pure touch sensation, you wouldn’t be able to tell whether someone was punching your shoulder or whether you’d just bumped into a wall. Since you’d want to react very differently to those two situations, it’s important for your brain to be able to tell them apart effortlessly.
How does your brain accomplish this goal? To study this, scientists in London developed, of all things, a tickling machine. When a person presses a button, a robot arm brushes a piece of foam across the person’s own hand. If the robot arm brushes the hand as soon as she presses the button to activate it, the person feels the sensation but it doesn’t tickle. However, the effect can be enhanced by introducing a delay between the button press and the touch. A delay of one-fifth of a second is enough to fool the brain into thinking the robot’s touch has been delivered by someone else — and then it tickles.
Even better, if the robot’s touch is delivered in a different direction than the one in which the person pulls the lever, then a delay as short as one tenth of a second is enough to generate a tickling sensation. This experiment shows that, at least for tickling, your brain is best at predicting the sensory outcome of a movement on the time scale of a fraction of a second.
Should you cram for an exam?
We’ve all done our share of cramming. Nearly everyone gets into a situation at some point where they’ve fallen behind in class and there’s not enough time to catch up before the test. Studying intensively at the last minute may allow you to pass the exam, which certainly has some value, but it’s not the best use of your time. Why? Psychologists have known for more than a century that your brain retains many kinds of information longer if it has an opportunity to process what you’ve learned between training sessions.
How can you protect your brain as you get older?
The most effective approach to keeping your brain healthy with age turns out to be something you probably wouldn’t expect: physical exercise. Neurons need a lot of support to do their jobs correctly, and problems with an aging circulatory system can reduce the blood supply that brings oxygen and glucose to your brain. Regular exercise, of the type that elevates your heart rate, is the single most useful thing you can do to maintain your cognitive abilities later in life.
Elderly people who have been athletic all their lives are much better at executive-function tasks than sedentary people of the same age. This relationship could occur because people who are healthier tend to be more active, but that’s not it. When inactive people get more exercise, even in their seventies, their executive function improves in just a few months. To be effective, exercise needs to last more than thirty minutes per session and occur several times a week, but it doesn’t need to be extremely strenuous. (Fast walking works fine.) The benefits of exercise seem to be strongest for women, though men also show significant gains.
How does exercise help the brain? There are several possibilities, all of which could contribute to the effect. In people, fitness training slows the decline in cortical volume with age. In laboratory animals, exercise increases the number of small blood vessels (capillaries) in the brain, which would improve the availability of oxygen and glucose to neurons. Exercise also causes the release of growth factors, proteins that support the growth of dendrites and synapses, increase synaptic plasticity, and increase the birth of new neurons in the hippocampus. Any of these effects might improve cognitive performance, though it’s not known which ones are most important.
Beyond normal aging, exercise is also strongly associated with reduced risk of dementia late in life. People who exercise regularly in middle age are one-third as likely to get Alzheimer’s disease in their seventies as those who do not exercise. Even people who begin exercising in their sixties can reduce their risk by as much as half. See you at the gym!
Excerpted from “Welcome to Your Brain” by Sandra Aamodt and Sam Wang. Copyright (c) 2009, reprinted with permission from Bloomsbury USA.