Prologue
modern psychology accepts a mechanistic conception of mental life, one that is materialist (seeing the mind as a physical thing), evolutionary (seeing our psychologies as the product of biological evolution, shaped to a large extent by natural selection), and causal (seeing our thoughts and actions as the product of the forces of genes, culture, and individual experience). (Page 3)
My own view is that we can find a middle ground here. I think the scientific perspective at the core of modern psychology is fully compatible with the existence of choice and morality and responsibility. Yes, we are, in the end, soft machines—but not just soft machines. (Page 4)
1 “Brain Makes Thought”
Phineas Gage, Greg F., and so many others illustrate what the Nobel Prize-winning biologist Francis Crick calls the Astonishing Hypothesis: You, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules. 3 There’s a shorter version of this idea in one of Charles Darwin’s notebooks: “Brain makes thought.” (Page 10)
The philosophical term for the position of Darwin and Crick is “materialism” (there is another meaning of this word that has to do with money; ignore this). For the materialist, there is nothing but physical stuff. There are no immaterial souls. (Page 10)
People are more attracted to the doctrine of “dualism,” which is that the mind (or the soul) is a fundamentally different kind of thing than the body. We are not one; we are two—bodies and souls. This is an idea that’s present in most religions and most philosophical systems (Plato, for instance, was very much a dualist), but the most thoughtful and articulate defender of dualism was the philosopher René Descartes. In his honor, the idea that minds and bodies are distinct is often described as “Cartesian dualism.” (Page 10)
Descartes notes there’s one thing that cannot be doubted—our own existence as thinking beings. The famous line is Cogito ergo sum—I think, therefore I am. You might not be sure you have a body, but you can be sure that there is a you who is asking the question. (Page 12)
As for what Descartes could and could not imagine, many philosophers have pointed out that he was too quick to assume that such a conceptual exercise could tell us about how things really are. Yes, you can doubt that you have a body and can imagine yourself without one. But this doesn’t mean that this is possible. After all, I can imagine a spaceship moving faster than light—there are many in science fiction. Descartes’ method reflects how we think about minds, not what’s true about minds. (Page 13)
To be fair, the other option, that brains make thoughts, can be equally hard to stomach. Here’s Gottfried Leibniz in 1712: “In imagining that there is a machine whose structure would enable it to think, feel, and have perception, one could think of it as enlarged yet preserving its same proportions, so that one could enter into it as one does a mill. If we did this, we should find nothing within but parts which push upon each another, we should never see anything which would explain a perception.” (Page 14)
The brain is a mere one fiftieth of our body weight but consumes about a quarter of the calories we burn off when we are at rest—it’s an energy hog. The human brain is also humongous. Baby heads are bowling balls, which is one reason why human females, relative to females of other species, have such a prolonged and painful childbirth. (Page 16)
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One of the great scientific disputes of the last century was over how the message got across this passage. This was known as the War of the Soups and the Sparks; the options were chemical (soup) or electrical (spark). 22 Long story short, the Soups won. As Cajal discovered, when neurons fire, axons release chemicals that we now call neurotransmitters; these cross the synapses to act on the dendrites of other neurons. (Page 19)
One physicist, Emerson M. Pugh, wrote, “If the human brain were so simple that we could understand it, we would be so simple that we couldn’t.” (Page 21)
Neuroscience can be said to have properly begun when scholars started to put this strategy into practice, by looking at those sad cases where natural causes did the dismantling. In 1861, a French physician named Paul Broca discovered a patient who was intelligent and could fully understand what was said to him, but who could only produce one word, “tan,” which he said no matter what was said to him, usually twice in a row—“ tan, tan.” After he died an autopsy found brain damage in part of his frontal lobe, now known as Broca’s area. (Page 24)
A pretty metaphor I’ve heard envisions the brain as a peach—the skin is the cortex, and the subcortical structures are parts of the stone. (The flesh of the peach is the white matter, largely composed of glial cells.) (Page 25)
The first thing you notice when you look at a brain is that it’s all wrinkly. This is because it’s crumpled up. If you were to take a brain, pull out the cortex, and smooth it out, it’s about two feet square. (Page 26)
Fish don’t have any cerebral cortex, reptiles and birds have a little bit, mammals have more, and primates, including humans, have a (Page 27)
The difference between the sides is often exaggerated in popular articles. There is no such thing as “right-brain” people and “left-brain” people. Most of the functions of the brain are on both sides of the brain. Still, there are differences. The left side of the brain is usually more involved with language and with the capacity for reason and logic, while the right side of the brain is more involved with social processes, imagination, and music. Some of these right-left differences are inborn; others are produced by experience. (Page 28)
The halves of the brain connect to the world in accord with a principle of contralateral organization, which means that due to a quirk of evolutionary history that’s not entirely understood, your right brain sees the left side of the world and your left brain sees the right side of the world; your right hemisphere controls the left side of the body and your left hemisphere controls the right side of the body. (Page 28)
Some scientists and philosophers draw a disturbing conclusion from the split-brain cases. They argue that for all of us, including those with intact corpus callosa, each half of our brain can be seen as a separate person. There is the language-using you, the one who is mostly in charge, and this is who is reading these words. But there is another you, a silent partner, also conscious, sitting next to the language-using self. When you split the brain, you liberate this silent self from the dominant “you,” and the two selves may fight it out for control. But this radical conclusion is controversial, and there’s no consensus as to what’s really going on in the mind (or minds) of someone with a split brain. (Page 29)
Occasionally you bump into a neuroscientist who says that theirs is the real science. Sure, you can talk about ideas, emotions, short-term memory, and so on, but when you really get down to it, the serious theories will be about brain areas, neurons, and neurotransmitters. This is what matters. Neuroscience makes psychology irrelevant. This attack on psychology is based on a confusion about how scientific explanation works. Just because we know about molecular biology doesn’t mean that we stopped talking about hearts, kidneys, respiration, and the like. The sciences of anatomy and physiology did not disappear. Cars are made of atoms but understanding how a car works requires appealing to higher-level structures such as engines, transmissions, and brakes, which is why physics will never replace auto mechanics. (Page 30)
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I think part of the enthusiasm about brains reflects the commonsense dualism we talked about earlier. Occasionally when boasting about the effects of some sort of therapeutic or educational intervention, people claim, “It changes the brain!” But everything changes the brain. Reading this sentence just changed your brain, because you’re thinking about it and thinking takes place in the brain. Indeed, reading this sentence creates long-lasting changes in your brain, because you’re going to remember a bit of it tomorrow (I promise you), and this means that the structure of your brain has been modified by this experience. If there was some mental activity that didn’t change the brain, it would prove Cartesian dualism and would be one of the most amazing discoveries of our time. But this will never happen because Cartesian dualism is mistaken. (Page 31)
“A map—and at their best that is what fMRI data are—does not tell you how something works. Where is not how. The next time you read a claim that a particular ability, or emotion, or concept has been localized to a particular region of the human brain using fMRI, ask yourself, ‘So what?’” (Page 32)
2 Consciousness
We’ll see that behaviorists like B. F. Skinner believed that an adequate science of psychology would say nothing about conscious experience. After all, we don’t discuss consciousness when talking about rats, and we’re no different from rats. The cognitive psychologists who followed Skinner rejected just about all his views—except for that one. After all, we don’t discuss consciousness when talking about computers, and we’re no different from computers. (Page 35)
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Times have changed since my graduate student days. Consciousness is now front and center in the science of the mind, as it should be. Regardless of whether it’s essential for intelligence, no theory of psychology could be complete without it. (Page 36)
Questions of consciousness are also of moral importance. I’m comfortable swinging an ax against a tree because I am confident that it doesn’t feel anything. If I were to discover otherwise, I would probably stop. As the philosopher Jeremy Bentham put it, when it comes to moral issues, the relevant question isn’t whether something can reason or speak; it is whether it can suffer. 2 And suffering requires consciousness. (Page 37)