Fred Linge emerged profoundly changed from his journey of learning to live with traumatic brain injury (TBI). The purpose of this book is to take you on a journey toward understanding the link between brain and behavior: how the brain is organized to produce behavior. Evidence comes from studying three sources: (1) the evolution of brain and behavior in diverse animal species, (2) how the brain is related to behavior in typical people, and (3) how the brain changes in people with brain damage or other brain dysfunction. The knowledge emerging from these three lines of study is changing how we think about ourselves, how we structure education and our social interactions, and how we aid those with brain injury, disease, and disorder.

We will marvel at the potential for future discoveries. We will begin to understand how genes influence the brain’s structure and activity. We will learn how our experience in turn changes our genes. We will review developments in brain imaging techniques that allow us to watch our own brain in action as we think and solve problems or sleep. We will consider the goals of brain–behavior research in arresting the progress of brain disease and finding cures for brain disease and injury. We will marvel at the injured brain interacting with machines that serve as prosthetics. We will consider the possibility of repairing and even replacing malfunctioning brains. We will also consider the possibility of interacting with artificial brains—brains of our making that can, in principle, match our intelligence or perhaps even surpass it. Our journey will broaden your understanding of what makes us human.

3

The brain is a physical object, a living tissue, a body organ. Behavior is action, momentarily observable but fleeting. Brain and behavior differ greatly but are linked. They have evolved together: one is responsible for the other, which is responsible for the other, and so on. There are three reasons for linking the study of the brain to the study of behavior:

None of us can predict how the knowledge we gain about the brain and behavior may prove useful. A former psychology major wrote to tell us that she took our course because she was unable to register in a preferred course. She felt that, although our course was interesting, it was “biology, not psychology.” After graduating and getting a job in a social service agency, she has found to her delight that understanding the links between brain and behavior is in fact a source of insight into many of her clients’ disorders and the treatment options available for them.

Brain, the Anglo-Saxon word for the tissue found within the skull, is but a part of the human nervous system (Figure 1-1). Most connections between the brain and the rest of the body are made through the spinal cord, which descends from the brainstem through a canal in the backbone.

Together, the brain and spinal cord make up the central nervous system (CNS). The CNS is encased in bone, the brain by the skull and the spinal cord by the backbone, or vertebrae. The CNS is called central both because it is physically the nervous system’s core and is as well the core structure mediating behavior. All of the processes radiating out beyond the brain and spinal cord constitute the peripheral nervous system (PNS).

The human nervous system is composed of cells, as is the rest of the body, and these nerve cells, or neurons, control behavior most directly. Neurons in the brain communicate with one another, with sensory receptors in the skin, with muscles, and with internal body organs. As shown in Figure 1-2, the human brain comprises two major sets of structures. The cerebrum (forebrain), shown in Figure 1-2A, has two nearly symmetrical halves, called hemispheres, one on the left and one on the right. The cerebrum is responsible for most of our conscious behaviors. It enfolds the brainstem (Figure 1-2B), a set of structures responsible for most of our unconscious behaviors. The second major brainstem structure, the cerebellum, is specialized for learning and coordinating our movements. Its conjoint evolution with the cerebrum suggests that it assists the cerebrum in generating many behaviors.

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For his postgraduate research, our friend Harvey chose to study the electrical activity given off by the brain. He had decided that he wanted to live on as a brain in a bottle after his body died. He expected that his research would allow his bottled brain to communicate with others who could read its electrical signals. Harvey mastered the techniques used to study the brain’s electrical activity but failed in his objective, not only because the goal was technically impossible but also because he lacked a full understanding of what brain means.

Harvey clearly wanted to preserve not just his brain but his self—his consciousness, his language, and his memory. This meaning of brain refers to something other than the organ found inside the skull. It refers to the brain as the body organ that exerts control over behavior. It is what we intend when we talk of someone smart being a brain or speak of the computer that guides a spacecraft as being the vessel’s brain. The term brain, then, signifies both the organ itself and the fact that this organ produces behavior.

To return to Harvey’s experiment, the effect of placing even the entire CNS in a bottle would be to separate it from the PNS and thus from the sensations and movements the PNS mediates. Could the brain function without sensory information and without the ability to move? Some evidence suggests that it could not.

One line of research and philosophical argument, called embodied behavior, proposes that the movements we make and the movements we perceive in others are central to our behavior (Prinz, 2008). That is, we understand one another not only by listening to words but also by observing gestures and other body language. We think not only with silent language but also with overt gestures and body language. Thus, the brain as an intelligent entity cannot be divorced from the body’s activities.

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In the 1920s, Edmond Jacobson wondered what would happen if our muscles completely stopped moving, a question relevant to Harvey’s experiment. Jacobson believed that, even when we think we are entirely motionless, we still make subliminal movements related to our thoughts. The muscles of the larynx subliminally move when we think in words, for instance, and we make subliminal eye movements when we imagine or visualize some action or a person, place, or thing. In Jacobson’s experiment, then, people practiced “total” relaxation and were later asked what the experience was like. They reported a condition of mental emptiness, as if the brain had gone blank (Jacobson, 1932).

In 1957, Woodburn Heron investigated another question related to Harvey’s experiment: How would the brain cope without sensory input? He examined the effects of sensory deprivation, including feedback from movement, by having participants each lie on a bed in a bare, soundproof room and remain completely still. Padded tubes covered their arms so that they had no sense of touch, and translucent goggles cut off their vision. The participants reported that the experience was extremely unpleasant, not just because of the social isolation but also because they lost their focus. Some even hallucinated, as if their brain was somehow trying to create the sensory experiences that they suddenly lacked. Most asked to be released from the study before it ended.

Findings from these lines of research suggest that (1) the CNS needs ongoing sensory stimulation from the environment and from its own body’s movement and (2) the brain communicates by producing movement and observing others’ movements. Thus, when we use the term brain to mean an intelligent, functioning organ, we are referring to an active brain that is connected to the rest of the nervous system and producing behavior.

Yet other evidence suggests that the brain can produce levels of consciousness with greatly reduced sensory and motor stimulation. When Martin Pistorius was 12 years old, his health began to deteriorate. Eventually, he lapsed into a coma. His parents placed Martin in a nursing home, where over a number of years he became conscious of his condition, locked-in syndrome, although he remained completely paralyzed and unable to communicate.

Martin’s condition persisted until, when he was 25, a nurse noticed him making some small facial movements. He seemed to be trying to communicate. With rehabilitation, he made excellent progress toward recovering movement, including using a voice synthesizer. Pistorius has since married. His book Ghost Boy describes his frustration and helplessness during years of enduring locked-in syndrome. We return to this idea of the nature of consciousness in Section 1-2.

Patients such as Martin Pistorius reveal that the brain can be conscious to a great extent in the absence of overt behavior. Whether it can maintain consciousness in the absence of all movement and sensory experience, the goal of Harvey’s brain in a bottle experiment, remains unknown.

Irenäus Eibl-Eibesfeldt began his textbook Ethology: The Biology of Behavior, published in 1970, with the following definition: “Behavior consists of patterns in time.” These patterns can be made up of movements, vocalizations, or changes in appearance, such as the facial movements associated with smiling. The expression patterns in time includes thinking. We cannot directly observe someone’s thoughts. The changes in the brain’s electrical and biochemical activity that are associated with thought show, however, that thinking, too, is a behavior that forms patterns in time.

The behavioral patterns of animals vary enormously. Animals produce behaviors that consist of inherited responses, and they also produce learned behaviors. Most behaviors consist of a mix of inherited and learned actions. Figure 1-3 illustrates the contributions of mainly inherited and mainly learned behavior in the eating behavior of two animal species, crossbills and roof rats.

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A crossbill beak seems awkwardly crossed at the tip, yet it is exquisitely evolved to eat pine cones. If its shape is changed even slightly, the bird is unable to eat the pine cones it prefers until its beak grows back. For crossbills, eating is largely a fixed behavioral pattern: it is inherited and does not require much modification through learning. Roof rats, in contrast, are rodents with sharp incisor teeth that appear to have evolved to cut into anything. Pine cones are an unusual food for the rats, although they have been found to eat them. But roof rats can eat pine cones efficiently only if an experienced mother teaches them to do so. This eating is not only learned, it is cultural in that parents teach it to offspring. We expand on the concept of culture in Section 1-5.

The mixture of inherited and learned constraints on behavior varies considerably from species to species. Generally, animals with smaller, simpler nervous systems exhibit a narrow range of behaviors that depend mainly on heredity. Animals with complex nervous systems have more behavioral options that depend on learning. We humans believe that we are the animal species with the most complex nervous system and the greatest capacity for learning new responses. Most of our most complex behaviors, including reading, writing, mathematics, and using smartphones, were learned long after our brain evolved its present form.

But most human behaviors retain some mixture of inheritance and learning, because we humans have not thrown away our simpler nervous systems. Like other animals, we retain many inherited ways of responding. The sucking response of a newborn human infant, for example, is an inherited eating pattern, but later in life eating is strongly influenced by learning and by culture.

Neuroscience in the Twenty-First Century

Before you continue, check your understanding.

Question 1

Question 2

Question 3

Question 4

Question 5

Answers appear in the Self Test section of the book.