While watching late-night television, you come across an infomercial for all-natural BrainGro. “It’s a well-known fact that most people use only 10 percent of their brain,” the spokesman promises, “but with BrainGro you can increase that number from 10 percent to 99 percent!” Why should you be skeptical of the claim that we use only 10 percent of our brains? What would happen if a drug actually increased neuronal activity by ten-fold?

Your friend has been feeling depressed and has gone to a psychiatrist for help. “He prescribed a medication that’s supposed to increase serotonin in my brain. But my feelings depend on me, not on a bunch of chemicals in my head,” she said. What examples could you give your friend to convince her that hormones and neurotransmitters really do influence our cognition, mood, and behaviour?

A classmate has read the section in this chapter about the evolution of the central nervous system. “Evolution is just a theory,” he says. “Not everyone believes in it. And, even if it’s true that we’re all descended from monkeys, that doesn’t have anything to do with the psychology of humans alive today.” What is your friend misunderstanding about evolution? How would you explain to him the relevance of evolution to modern psychology?

A news program reports on a study (Hölzel et al., 2011) in which people who practised meditation for about 30 minutes a day for 8 weeks showed changes in their brains, including increases in the size of the hippocampus and the amygdala. You tell a friend, who is skeptical. Your friend says “The brain doesn’t change like that. Basically, the brain you’re born with is the brain you’re stuck with for the rest of your life.” Why is your friend’s statement wrong? What are several specific ways in which the brain does change over time?

A friend of yours announces that he has figured out why he is bad at math. “I read it in a book,” he says. “Left-brained people are analytical and logical, but right-brained people are creative and artistic. I’m an art major, so I must be right-brained, and that’s why I’m not good at math.” Why is your friend’s view too simplistic?