47

IN THE LINE OF FIRE It was November 9th, 2004, and U.S. Marine Brandon Burns was surrounded on all sides by gunfire. The enemy was everywhere, in the buildings, streets, and alleyways of Fallujah. “I was in the deepest part of the city [and] there was chaos,” remembers Brandon. At age 19, Brandon was on the front lines in the Iraq War, fighting in the battle of Fallujah.

“I was on top of the Humvee automatic grenade launcher shooting round after round,” Brandon recalls. Suddenly, there was darkness. A bullet from an enemy sniper had pierced Brandon’s helmet and skull, and ricocheted through the back left side of his brain. Bleeding and unconscious, Brandon was rushed from Fallujah to Baghdad. Medics had to resuscitate him on five separate occasions during that ambulance ride. Brandon explains, “Five times I died.”

From Baghdad, Brandon was transferred to a hospital in Germany. Doctors concluded that some parts of his brain were no longer viable. “They removed part of my skull and dug out the injured part of my brain,” and now, Brandon says, “one third of my brain is gone.”

Note: Quotations attributed to Brandon Burns, Laura Burns, and Christina Santhouse are personal communications.

48

Imagine that you lost a sizable chunk of your brain. How would it impact your life? Would you be the same person as before? Your brain houses your thoughts, emotions, and personality, and orchestrates your behavior. It files away all your memories and dark secrets, and is involved in your every move, from the beat of your heart to the blink of your eye.

However, the human brain is only one part of the most complex living entity known. The human nervous system is a communication network that conveys messages throughout your body, using electrical and chemical processes. The nervous system contains the brain, spinal cord, and other nerves and fibers, and includes some 100 billion (10¹¹) nerve cells. For a sense of what that number represents, consider that the population of the United States was approximately 320 million people in 2015; the number of nerve cells is approximately 313 times the number of people living in the United States. These cells are interlinked through some 100 quadrillion (10¹⁵) connections (Tang, Nyengaard, De Groot, & Gundersen, 2001). This intricate, ever-adapting web of connections gives us the power to think and feel in ways that are different from—and vastly more complex than—the thinking and feeling capacities of most other organisms.

Consider the many tasks your brain is juggling at this very moment. As you scan the words on this page, your brain helps control the tiny muscles moving your eyes back and forth as well as the larger muscles in your neck and torso that keep you sitting upright. Light-sensitive cells in the back of your eyes relay signals, using electricity and chemicals, to various brain regions that transform the black marks on this page into words, sentences, and ideas for you to remember. And all the while, your brain is processing nonvisual sensory input such as sounds and smells, and working with other nerve cells in your body to make sure your heart keeps pumping, your lungs keep breathing, and your glands and organs keep releasing hormones properly.

LO 1 Define neuroscience and biological psychology and explain their contributions to our understanding of behavior.

Brandon’s injury resulted in a significant loss of his brain tissue. Remarkably, not only did he survive, but he can still talk about what occurred, think about the events, and feel emotions regarding what happened to him. How exactly does his brain orchestrate all these complex functions, especially after severe trauma? And how does a noninjured brain carry out these complicated processes? Scientists have developed a decent understanding of how individual brain cells communicate with each other, but they have yet to provide definitive answers to “big questions” involving the brain and other parts of the nervous system such as: How do we think? What is consciousness? Why must we sleep? This is why the brain may be regarded as the last frontier of medicine. Neuroscience, the study of the brain and nervous system, actually extends far beyond the borders of medicine and into disciplines as diverse as engineering, computer science, and our personal favorite—psychology. The subfield of psychology concerned with understanding how the brain and other biological systems influence human behavior is called biological psychology, which brings us to the goal of this chapter: to examine how biology influences our behavior.

49

LO 2 Compare and contrast tools scientists use to study the brain.

Brandon underwent many brain scans before and after his surgeries, which allowed doctors to get a detailed look inside his head without lifting a scalpel. But had Brandon lived in a different era, brain scans would not have been an option.

Before there were technologies to study the brain, people could only speculate about what was going on beneath the skull of a living person. One theory was that bumps on a person’s skull could reveal characteristics about him. Judging the topography of a person’s head was a core part of phrenology, the now discredited brain “science” that achieved enormous popularity at the beginning of the 19th century through its founder Franz Joseph Gall (1757–1828). Another early (but more scientific) way of studying the brain was through ablation, a technique used by physiologist Pierre Flourens (1794 –1867) to determine the functions of different brain regions (Pearce, 2009). This technique involved destroying parts of a living animal’s brain and then determining whether some functioning was lost following this surgery. In spite of the limitations of their methodologies, Gall and Flourens advanced the idea that there might be areas of the brain with particular functions. In other words, there are locations in the brain that are responsible for specific brain activities: there is a localization of function.

Brain research has come a long way since the days of Gall and Flourens. The last century, and particularly the last few decades, has witnessed an explosion of technologies for studying the nervous system (see Infographic 2.1 below). Such advances have made it possible to observe the brain as it makes decisions, sleeps, and even tells lies (Dang-Vu et al., 2008; Hampton & O’Doherty, 2007; Kozel et al., 2009). See Table 2.1 for information on the scope and limitations of these technologies.

50

51

With that overview, we are now ready to begin our chapter-long “learning tour” of the nervous system. Our journey begins in the microscopic world of nerve cells, or neurons. Neurons are specialized cells that communicate with each other through both electrical and chemical signals. They are the building blocks of the brain, spinal cord, and nerves. When large numbers of these building blocks are lost or damaged, as occurred in Brandon’s injury, the consequences can be severe.

Question 1

1. consciousness

2. the human nervous system

3. a neuron

4. the skull

Question 2

Question 3