Define physiological psychology

Define physiological psychology

artin/Images.com/Corbis Learning Objectives After completing this chapter, you should be able to: Define physiological psychology and explain what this field studies. Discuss the difference between cardiocentric and encephalocentric views of behavior and identify ancient scholars associated with each viewpoint. Describe the difference between holism and localization and explain why most brain scientists favor localization. Define the word multidisciplinary and explain why neuroscience is a multidisciplinary field. Contrast the ways behavioral neuroscientists and cognitive neuroscientists study the brain and behavior. Create a table showing the various brain lesioning and stimulation methods and the instrumentation needed to perform these techniques. Evaluate the advantages and disadvantages of each of the brain imaging and brain recording methods. Explain the difference between correlation and causation and generate examples of each. Distinguish biological explanations from other explanations of behavior. Tyrone was riding in the front passenger seat of his roommate’s car when the driver lost control of the car on an icy road. The car slid off the shoulder of the road and collided with a guardrail. Because he was not wearing a seat belt, Tyrone was thrown forward in the impact, and his head struck the dashboard with intense force. For several minutes, Tyrone was unconscious, although he was able to respond to rescue workers when they arrived to transport him to the hospital. He was released from the hospital in seemingly good health, but he began to develop some troubling symptoms within a couple of days. For example, he began to accuse his roommate of stealing his clothes and money. Then he became convinced that his girlfriend was cheating on him. When he attacked a stranger at a local shopping center because the stranger nodded and smiled at Tyrone’s girlfriend, Tyrone was placed in the care of a neurologist (a physician who specializes in the treatment of brain disorders). The neurologist ordered scans of Tyrone’s brain, which indicated an accumulation of fluid within his brain, a condition known as hydrocephalus. In rare cases like Tyrone’s, hydrocephalus can produce paranoia, delusions, and violent behavior (Bloom & Kraft, 1998). He was referred to a neurosurgeon, who inserted a very thin tube into Tyrone’s brain to allow the excess fluid to drain out of the brain. The reduction in fluid within his brain eliminated Tyrone’s symptoms, and he was able to go back to a normal life. An accidental bump to his head caused fluid to build up within Tyrone’s brain, changing his behavior in a disturbing manner. Modern brain imaging and surgical techniques helped restore Tyrone to health. An impressive body of research involving the brain and behavior has enabled scientists and practitioners to develop techniques that permit diagnosis and treatment of a wide variety of disorders that affect the brain. However, since the dawn of humankind, people have sustained head injuries or developed brain diseases, and there is amazing evidence that the earliest humans tried to treat those unfortunate victims of accident and disease. An image of an ancient Peruvian skull with a surgical hole in the top. Kjell B. Sandved/Science Source Photo 1.1 Although it is clear that craniotomies were the first form of brain surgery, we are unsure exactly why they were performed. What do you speculate the ancient peoples were trying to do? Take a close look at Photo 1.1 below. This is a skull of one of the native people from South America, estimated to be thousands of years old. You will notice a large hole where the skull has been punctured by sharpened stones in a procedure called a craniotomy. What’s more, there is evidence that many of the “patients” who received this crude, prehistoric surgery lived weeks, months, or even years following the craniotomy, or skull incision. It is not known why craniotomies were performed, since these crude surgeries were conducted before the advent of written history, so the story behind them has disappeared. Anthropologists have speculated that craniotomies were performed to permit the escape of evil spirits. Perhaps the person was depressed, psychotic, or physically ill, and the local medical practitioner performed the craniotomy in a ritual meant to draw out the evil spirit that was causing the distress (Stewart, 1958). Practitioners of Western medicine no longer believe that evil spirits produce disordered behavior. As a result of careful research and observation, our understanding of the biological foundations of behavior has become quite sophisticated. In Chapter 1 we will examine how knowledge of the workings of the brain developed. We will review modern techniques for studying the brain, and we will conclude the chapter with a consideration of biological explanations of behavior. 1.1 Ancient Explanations of Behavior The concept of a brain did not figure prominently in the recorded histories of most early societies. In ancient China, more than 40 centuries ago, medical personnel such as Shun Nung (circa 3000 BCE) and Huang Ti (circa 2700 BCE) treated mental afflictions with acupuncture and herbal remedies aimed at balancing the yin and yang and freeing the life energy known as chi. The distinguished scholars Hua T’o (100 CE) and Chang Chung-Ching (200 CE), who perfected the art of Chinese medicine, prescribed treatment for the 12 major organs, which did not include the brain. Heart-Centered Explanations for Behavior Cardiocentric explanations, or heart-centered explanations, of behavior were popular in the great ancient civilizations of Western history, including those in Egypt and Greece. According to cardiocentric explanations, the heart produces and regulates all behaviors, including thoughts and emotions (cardio means “heart” in Latin). The brain was not considered a vital organ by the early Egyptians and was removed through the nose and discarded before mummification of a corpse, whereas the heart was preserved for use by the departed in the afterlife. Aristotle (384–322 BCE) considered the heart to be the organ of intelligence (Spillane, 1981). In his own observations, Aristotle noticed that poking the brain of an injured person did not induce pain (see “For Further Thought: Why Doesn’t Poking the Brain Produce Pain?”). Aristotle reasoned that the brain is not involved in pain perception nor, he concluded, in any other type of perception. The function of the brain, according to Aristotle, was to cool the heart. For Further Thought: Why Doesn’t Poking the Brain Produce Pain? A doctor performing brain surgery on a conscious patient. Burger/Phanie/SuperStock Photo 1.2 Why do you think patients need to be conscious during brain surgery? As you will learn later in this chapter, brain surgery is sometimes performed on people who are conscious and can respond to questions during the surgery. A local anesthetic (an- means “without” and -esthesia means “feeling” in Latin), similar to the drug that your dentist uses to numb a tooth, is injected into the scalp (see Photo 1.2) and the connective tissue covering the skull to eliminate the sensation of pain as the surgeon cuts through the scalp and skull to reach the brain. Once inside the skull, however, no painkillers are necessary. In order to feel pain, special nerve cells called pain receptors are needed. Pain receptors are located throughout the skin, muscles, and bones in the body. When these pain receptors are stimulated, messages about pain are sent to the brain, and pain is experienced. The brain contains no pain receptors. Thus, no anesthesia is required as the surgeon cuts through tissue in the brain. Aristotle studied all kinds of animals, from tiny rodents to elephants. He observed that the body grows cold when the heart stops beating, which led him to believe that the heart produces the body’s heat. It occurred to Aristotle that a mechanism was needed to cool the incessant heart, and he assigned this function to the brain. In addition, scholars in Aristotle’s time knew that the human voice is produced by air exhaled from the lungs. Aristotle reasoned that the words are supplied by the heart and, therefore, that the words and voice roll out of the chest cavity together. Aristotle’s cardiocentric view survived into the Middle Ages. As late as the 16th century, medical students and students of anatomy were taught that nerves, like all veins and arteries, originate from the heart. Anatomical dissection studies demonstrated that arteries, veins, and nerves course through the body bundled together in sheaves. Tracing the veins and arteries back to the heart led to the obvious, but erroneous, conclusion that the nerves also come from the heart. 1.2 Brain-Centered Explanations of Behavior Many ancient Greeks did not agree with Aristotle’s cardiocentric view, however. Encephalocentric explanations, or brain-centered explanations, of behavior came about as a result of dissection studies of human and other animal cadavers (encephalon means “brain” in Greek). Known as the father of medicine, Hippocrates (460–377 BCE) supervised dissections of human bodies on the island of Cos in ancient Greece. These dissections led to the discovery of nerves and nerve function. Galen (130–200 CE), often called the father of experimental physiology, also disagreed with Aristotle’s cardiocentric view. He reasoned that, if indeed the function of the brain is to cool the heart, it would be located closer to the heart. His own work indicated that the brain is of paramount importance. In one experiment, Galen cut through the medulla, right above the spinal cord in the brain, and observed that breathing ceased. This led him to conclude that the brain controls respiration (Spillane, 1981). Galen firmly established the brain’s central role in human behavior. Since Galen’s time, over many centuries, scientists studied the anatomy of the brain, cataloguing its many structures, cavities, fissures, and bulges. But descriptions of the brain’s functioning were pure fantasy until the 19th century, when formal study of the brain began. Controlled experiments involving the brain were rare until the 19th century. Before 1800 most knowledge about the brain came from observations of people who suffered head injuries, such as a kick in the head from a horse or a gunshot wound to the head. It was observed that people who received injuries to the back of the head invariably had visual or motor impairments afterward. Those who incurred head wounds to the front of the brain often showed memory or personality disturbances. However, there was much disagreement over the extent to which specific behaviors could be localized to discrete brain areas (Poldrack, 2010). Holism Versus Localization Vicious scientific debates ensued over whether the brain divides its labors. Those who supported the concept of holism claimed that every area of the brain is equally capable of controlling all human functions. The proponents of localization argued that human functions are regulated by distinct, specific areas of the brain. Most of the credit for popularizing the concept of localization goes to a highly regarded neuroanatomist, Franz Gall, who is best remembered today for developing the field of phrenology (Goodrich, 2013). Image of a bust with the head divided into different sections, each section labeled differently. Science Source Photo 1.3 This sketch depicts Franz Gall’s localization of brain functions. His findings changed the ways in which scientists and medical professionals thought about the organization of the brain. From an early age, Gall was fascinated by the shapes of people’s heads. Young Franz, at age 9, was quite impressed by his observation that his classmates with bulging eyes had excellent verbal memories—or memory for words and language. As an adult he studied hundreds of human skulls. Gall scoured hospitals, prisons, asylums, and schools, looking for odd-shaped heads and people with notable talents or dispositions (Spillane, 1981). Gall was convinced that lumps on the outside surface of the brain correspond to human capacities such as thrift, courage, love, or jealousy (see Photo 1.3). Furthermore, he theorized that the shape of the skull reflects the shape of the lumpy, bumpy brain beneath and that a person’s psychic endowments could be measured by examination of the skull’s shape. So popular was Gall’s phrenology by the beginning of the 19th century that the ancient Egyptian practice of head shaping, or applying pressure to the supple skulls of babies with cloth wrappings, returned. Whereas the Egyptians used head shaping to produce a more flattened, elongated skull, which was considered quite beautiful and desirable in their time, 19th-century Europeans used head shaping to encourage the development of qualities such as intelligence and moral character in their children (Fishman, 1988). Head shaping aside, Gall’s theory of localization, although not based on experimental evidence, changed the way many scientists began to think about the organization of the human brain. It appeared that the brain divides its labor, one part specializing in vision, for example, and another part specializing in speech. Scientific investigations conducted in the 19th century provided evidence to support the notion of localization. 1.3 The Development of Brain Science Julien Jean Cesar Legallois is credited with providing the first evidence in support of localization of function in 1812 (Nanda, 2012). He was able to demonstrate that a specific area of the medulla controls breathing. In 1861 the French physician Paul Broca reported the results of a postmortem examination of the brain of a man nicknamed “Tan” by other patients. Tan had suffered a stroke 2 decades earlier and had been able to utter only one syllable, “tan,” since the stroke. The autopsy that Broca performed on Tan’s brain revealed damage to a distinct area in the front portion of the left half of the brain (Figure 1.1). This area, today called Broca’s area after the French doctor who discovered it, is known to control the production of speech. Figure 1.1: Broca’s area Damage to Broca’s area typically results in disordered speech production. A head showing the location of Broca’s area in the brain, which is set behind the eyes. The Motor Cortex Two German investigators, Gustav Fritsch and Eduard Hitzig, demonstrated in 1870 that specific areas of the motor cortex control particular movements of the body. When the investigators electrically stimulated the motor cortex near the top of the brain, a dog’s hind legs would wiggle. Stimulation of the motor cortex toward the bottom of the brain produced jaw movements. A Scottish physician, David Ferrier, documented the same findings in monkeys in 1876. In 1874 an American physician, Roberts Bartholow from Cincinnati, Ohio, stimulated the cortex of a female patient who had an extensive skull fracture following an accident. Bartholow was able to produce movements of specific muscles, depending on the placement of the stimulating probe on the woman’s exposed motor cortex (Valenstein, 1973). This precise mapping of the body onto an area of the brain is called topographical organization. Figure 1.2 illustrates the topographical organization of the motor cortex in humans: this odd-shaped creature is called the motor homuculus. The motor cortex is organized in such a way that specific cells in the motor cortex control certain muscles in the body. Areas of the motor cortex near the top of the head command muscles in the feet and legs, whereas lower areas of the motor cortex command muscles in upper regions of the body. Ferrier’s research also showed that the somatosensory cortex, which is located next to the motor cortex, is topographically organized. Stimulation of different parts of the somatosensory cortex produces sensations in specific areas of the body (Figure 1.3). You will discover as you read this book that several areas of the brain display topographical organization. Figure 1.2: Topographical organization of the human motor cortex Specific regions of the motor cortex of the human brain control particular muscles in the body. A detailed version of parts of the motor cortex and the parts of the body it controls: toes, ankle, knee, hip, trunk, shoulder, elbow, wrist, hand, little finger, ring finger, middle finger, index finger, thumb, neck, brow, eyelid and eyeball, face, lips, jaw, tongue, and swallowing. On the right is a brain, showing the motor cortex positioned next to the sensory cortex. Figure 1.3: Topographical organization of the somatosensory cortex Stimulation of specific regions of the sensory cortex of the human brain produces sensations in particular areas of the body. An enlarged depiction of the sensory cortex and its location in the brain. A detailed version of parts of the sensory cortex and the parts of the body it produces sensations in: genitals; toes; foot; leg; hip; trunk; neck; head; shoulder; arm; elbow; forearm; wrist; hand; little finger; ring finger; middle finger; index finger; thumb; eye; nose; face; upper lips; lower lips; teeth, gums, and jaw; tongue; pharynx; and inter-abdominal. On the right is a brain, showing the motor cortex positioned next to the sensory cortex. Soon after Ferrier reported his research on monkeys, scientific journals began to publish dozens of papers linking particular brain areas to specific behaviors. Despite the mounting evidence in support of localization, a number of highly regarded scholars refused to view the brain as anything more than an undifferentiated mass. As late as the 20th century, a prominent American psychologist, Karl Lashley, conducted a number of experiments on rat learning and intelligence that he claimed demonstrated support for the concept of holism (Lashley, 1929). Wilder Penfield’s Experiments Four images of a brain, each with a different area lit up. WDCN/Univ. College London/Science Source Photo 1.4 In the upper left, sight activates the visual area in the occipital cortex. In the upper right, hearing activates the auditory area in the temporal cortex. In the lower left, touching Braille script activates the tactile area in the parietal cortex and an area of cognition. In the lower right, activation of the frontal cortex occurs during word generation while speaking. Wilder Penfield, a Canadian neurosurgeon, conducted experiments in the 1940s and 1950s on the exposed brains of awake but sedated patients while their skulls were open during surgery (Penfield, 1977). Using a 3-volt battery, he stimulated different areas of the cortex with a probe. Memories were elicited when some areas of the brain were stimulated. For example, patients would describe a childhood sweetheart or a room in an old home when areas toward the back of the cortex were excited. Stimulation in the somatosensory cortex produced sensations in various parts of the body, depending on the location of the electrical probe. In fact, it was this research by Penfield that inspired the drawings of the homunculi in Figures 1.2 and 1.3. Penfield’s work left no doubt that the brain is composed of many discrete regions that have specialized functions. Modern brain imaging techniques permit investigators to pinpoint active regions of the brain associated with particular behaviors (Photo 1.4). (You will learn more about these techniques later in this chapter.) Brain imaging studies have fueled the imaginations of scientists, journalists, and dreamers alike. Current imaging studies attempt to conclude whether or not the same neural circuits are activated by pleasurable, stressful, and normal sensations such as sexual arousal, car accidents, or doing laundry (Lang & Bradley, 2010). 1.4 Studying the Brain and Behavior The history of brain science is relevant to a variety of fields of study, including neuroscience, behavioral neuroscience, cognitive neuroscience, and physiological psychology. Let’s take a brief look at each of these fields. Behavioral and Cognitive Neuroscience Neuroscience is a multidisciplinary approach to studying the brain. Multidisciplinary means that many different fields or disciplines contribute to this science (multi means “many” in Latin). Biologists, chemists, physicists, anatomists, physiologists, psychologists, mathematicians, and engineers work together to unlock the mysteries of the brain. Undergraduate or graduate students majoring in neuroscience are expected to have a strong background in the natural sciences and mathematics. Behavioral neuroscience and cognitive neuroscience are specialized branches of both neuroscience and psychology. In general, psychologists who study the brain and behavior are usually classified as behavioral neuroscientists or cognitive neuroscientists, depending on their method of study. Behavioral neuroscience involves bottom-up research strategies in which brain function is manipulated and the effect on behavior measured. Bottom-up research strategies begin by studying the main cell of the brain, called the neuron, and its interactions with other neurons. Behavioral neuroscientists strive to learn about the basic levels of brain function in order to understand higher level functions like thought, attention, and emotion. In contrast, cognitive neuroscience is characterized as a top-down approach in which the highest levels of functioning, cognitive events like thinking or problem solving, are manipulated in order to observe the effect on neurons (Johnson, 2011). Top-down research strategies involve studying high-level cognitive functions in order to draw conclusions about functions at the cellular levels. Physiological Psychology The foundation text on physiological psychology was published in 1904 by Wilhelm Wendt. Like behavioral neuroscience, physiological psychology uses a bottom-up approach to studying the brain and behavior. The term physiological psychology can be used interchangeably with the term behavioral neuroscience. In this textbook, we will look at emotions and cognitive functions, which are typically studied in top-down experiments with human subjects. We will also look at movement, sensory processes, motivation, and homeostatic regulation, behavioral processes that have traditionally been examined using bottom-up approaches and laboratory animal subjects. Both bottom-up and top-down approaches have generated a wealth of knowledge that has added to our understanding of the brain and behavior. Animals as Research Subjects Photo of a woman holding a megaphone and two women holding a banner that says “Abolish Vivisection.” There are policemen in riot gear standing to the right of the protesters. Peter Marshall/Demotix/Corbis Photo 1.5 Much debate surrounds animal testing, such as whether it is ethical and if its findings are accurate. You might be thinking, “Why in the world would anyone want to experiment with animals? That sounds cruel.” If you feel this way, you are not alone (Photo 1.5). Many people, including some scientists, are opposed to the use of animals as research subjects (Farnaud, 2009). A number of experts believe that the usefulness of animal models is especially limited when studying behavior, particularly higher functions like thinking and language. But these objections to animal research are not new. David Ferrier, whose historic experiments with monkey brains are described earlier in this chapter, was arrested under the Cruelty to Animals Act of 1876 in Great Britain. (He was later acquitted of these charges.) Some authors argue that not only is experimentation on animal subjects cruel, it also produces misleading findings (Farnaud, 2009). There is no denying that all species are unique in some respects and that the unnatural environment of the laboratory can bias results. However, the judicious use of nonhuman subjects can provide important findings that can be used to improve the lives of humans and other animals and to add to our understanding of brain organization and function (Nestler & Hyman, 2010). Examples of important medical developments that required animal research are listed in Table 1.1. Although species might differ in some aspects of their physiology, cellular and biochemical mechanisms are generally the same for all animals. For that reason, we can generalize from the activity in a squid neuron to that in a human brain cell. Table 1.1: Benefits of animal research: Medical advances that required animal research for their development Benefits to Humans •Immunization against polio, diphtheria, mumps, measles, rubella, and smallpox •Antibiotics •Anesthetics and other painkillers •Blood transfusions •Radiation and chemotherapy for cancer treatment •Open-heart surgery for coronary bypass and correction of birth defects •Insulin treatment for diabetes •Asthma medication •Medication for epileptic seizures •Organ transplantation and drugs to prevent organ rejection •Medications to treat depression, anxiety, and psychosis •Microsurgery to reattach severed limbs •Rehabilitation of stroke and brain-damaged accident victims Benefits to Animals •Vaccination against rabies, distemper, tetanus, and other infections •Corrective surgery for hip dysplasia in dogs •Orthopedic surgery and rehabilitation for horses •Treatment for leukemia and other cancers in pets •Improved nutrition for pets Source: Foundation for Biomedical Research. (1988). The use of animals in biomedical research and testing. Washington, DC: Foundation for Biomedical Research. Regulation of Use of Animals in Research All research involving animals is strictly regulated by the U.S. government under the Animal Welfare Act of 1966 and by the institution in which the research is conducted. Today close monitoring and regulation of research involving vertebrate animals go on in all research institutions. The Animal Welfare Act requires that all experiments with nonhuman subjects be approved by a committee composed of scientists and nonscientists, called an institutional animal care and use committee (IACUC), before they are conducted. An IACUC is also charged with the responsibility of regularly inspecting the animal living quarters and other research areas. When designing an experiment, the behavioral scientist must decide which species is going to be used as subjects. There is now widespread recognition that nonhuman subjects are never as good a choice as human subjects in studies of human behavior. Since the 1970s, the decreased number of laboratory experiments on animals can be attributed to both scientific community reconsiderations and the 1976 Animal Welfare Act in the United States (Adams & Larson, 2012). All scientists who use nonhuman subjects in their laboratory experiments must balance the need for valid scientific data with the demand for the humane treatment of animals. However, when a bottom-up approach is used to study brain processes, nonhuman subjects are the best and sometimes the only choice (Gill, Smith, Wissler, & Kunz, 1989). The American Psychological Association (APA) has also established guidelines for psychologists working with nonhuman animals, which can be found at the APA website. 1.5 Modern Neuroscientific Research Methods Early investigators used two techniques to study the brain: lesioning and stimulation. Lesioning involves damaging or disrupting the function of a particular area of the brain. If a region of the brain is destroyed, then it cannot perform its usual function. The investigator would typically produce a lesion in an area of interest in the brain of an anesthetized animal. When the experimental subject recovered from the surgery, the investigators observed its behavior for any signs of impairment. Lesioning, then, demonstrates what happens when a brain structure is not functioning normally. Most of the earliest lesioning studies involved ablation, or removal of a part of the brain. In the first studies, the brain region to be removed was merely ladled out with a sharp spoon. However, this rather crude procedure created a bruised area in the brain that became scarred and prone to produce epileptic seizures. Karl Lashley, the American psychologist you learned about earlier in this chapter, used a technique called hot wire thermocautery. After preparing his subject for the procedure, which involved anesthetizing it and opening its skull, Lashley placed the tip of a red-hot wire in the brain to burn away the area to be lesioned. This technique produced a neat lesion with little bleeding, but it did not eliminate scarring, which caused uncontrollable seizures. Wilder Penfield perfected a suctioning technique to lesion the brains. He used a pipette, which looks like a medicine dropper, to draw out the brain tissue. This technique was superior to Lashley’s because it produced minimal, if any, scarring. All brain cells that did not have a good blood supply were easily removed, which meant that no dead tissue was left in the brain after surgery. Penfield’s suctioning technique is still used today by neurosurgeons and neuroscience investigators to remove brain matter. Subcortical Lesions Ablation techniques work fine when a cortical area of the brain is under investigation. However, an entirely different technique is needed when lesioning a structure beneath the cortex, called a subcortical brain structure. Think about the problems that would be encountered in lesioning a subcortical structure. First of all, the subcortical structure is not visible when the skull is opened, and it has to be located underneath the overlying cortex. In addition, care must be taken to lesion the subcortical structure without damaging the overlying brain. How is it possible to locate and lesion subcortical structures? Think about how you might get to a city that you have never visited before. For starters, you might ask a friend how to get there, or you could pick up a road atlas and locate the city. And that’s exactly how brain investigators find unfamiliar brain structures: They consult with a colleague or read a published paper that describes another scientist’s research on that structure, or they use a stereotaxic brain atlas. A stereotaxic brain atlas contains dozens of maps of the brain, each map representing a slice through a particular region of the brain. There are atlases for human brains, dog brains, cat brains, rat brains, monkey brains, and even several species of bird brains. An apparatus called the stereotaxic instrument was developed in 1908 by Victor A. H. Horsley and Robert H. Clarke to enable investigators to locate brain structures with precision. Because subcortical structures can be quite small, they are easy to miss if measurements are not precise. The stereotaxic instrument consists of a platform on which the subject’s head is held securely in place and a measuring device that allows precise measurements to a tenth of a millimeter. Figure 1.4 illustrates a stereotaxic instrument used for human patients. Figure 1.4: Human stereotaxic instrument The stereotaxic intrument helps neurosurgeons locate structures before operating on them. Localization would take place earlier, via imaging. Drawing of human stereotaxic instrument being used on a person. Source: From Lars Leksell, Stereotaxic and Radiosurgery: An Operative System. 1971. Courtesy of Charles C. Thomas Publisher, Ltd., Springfield, Illinois. Equipped with a brain atlas and stereotaxic instrument, a neuroscientist is able to locate subcortical structures and lesion them. To produce a subcortical lesion, an insulated conducting wire, called an electrode, is inserted into the brain. An electrode is completely insulated except at its tip, which permits an electrical current to flow into the brain. Some of the earliest electrodes were merely sewing needles insulated with melted glass (Valenstein, 1973). In small animals, lesions are made with direct current (DC) electricity. Radio-frequency (RF) waves are used to produce a lesion in a larger animal, including humans. Because the brain has the consistency of thick pudding, passing a wire down through it does not cause noticeable damage to brain structures in the wire’s path. Only those structures surrounding the uninsulated tip of the electrode are destroyed during lesioning. Today neurosurgeons use sophisticated imaging techniques. Imaging techniques provide accurate localization of structures buried deep within the brain. Modern imaging systems allow minimal invasion of the brain and provide instant and continual navigational information during surgery. “For Further Thought: Neuronavigation, Navigating the Brain” describes one modern brain navigation technique. We will discuss additional imaging techniques later in this chapter. For Further Thought: Neuronavigation, Navigating the Brain A woman lying on an operating table while a surgeon operates on her brain. Her head is surrounded by plastic and wires, and she is looking off to the side James King-Holmes/Science Source Photo 1.6 Which technology do you think the doctor is using while this woman undergoes an awake craniotomy brain surgery? For many neurosurgeons today, brain surgery involves using technologically advanced systems that enable surgeons to localize and work in specific regions of the brain. In the past, stereotaxic instruments were the only apparatus available to locate targets in the brain. Today’s neurosurgeon has an array of neuronavigational devices that permit faster, more accurate, and less invasive surgeries. In Photo 1.6, you can see a typical modern surgery room, with computers and computer monitors providing a visual image of the patient’s brain as the surgeon moves a handheld localization device about the surgical site. The localization device is an interactive tool that links movement of the surgeon’s hand with the view of the brain presented on the computer screen. This localization device can help the surgeon visualize the position of major blood vessels and other brain structures that the surgeon will want to avoid during surgery. It also permits the surgeon to assess how much tumor remains hidden during surgery to remove a brain tumor. The main benefit of neuronavigational systems is that their use reduces the size of the craniotomy and the amount of brain tissue disturbed during surgery. The most modern subcortical lesioning techniques employ converging beams of ionizing radiation in procedures involving the gamma knife, the cyclotron, or linear accelerators (Figure 1.5). The area to be lesioned is located stereotaxically, and the lesioning rays are focused on that precise area of the brain. This noninvasive technique is preferred for producing lesions in human brains because the overlying and surrounding brain tissues are unaffected by the penetrating radiation. Tissue destruction only occurs at the point where the rays come together. Figure 1.5: The gamma knife hemisphere In the gamma knife procedure, the patient’s head is placed into a fixed helmet, which delivers 201 converging beams of gamma radiation. Each individual beam is very weak and cannot damage brain tissue. Tissue destruction occurs where the beams converge and meet. This is the preferred method of surgical intervention for patients with pineal gland tumors. Labeled parts of the gamma knife hemisphere, including the couch, shielding door, collimator helmet, upper hemispherical shield, collimator, beam sources, and the case shield. Brain Stimulation Brain stimulation is another method for determining the function of a specific area of the brain. The stimulation method causes a part of the brain to become active. This can be accomplished either by excitatory chemicals injected into the brain or alternating current (AC) electricity, which is delivered through electrodes. The earliest investigators (like Gustav Fritsch and Eduard Hitzig, who stimulated the brains of dogs) studied the effects of stimulation in anesthetized subjects. While a dog was unconscious, they opened its skull and touched electrodes to the surface of the motor cortex, passing a stimulating electrical current into the brain and noting contractions of the dog’s muscles. Obviously, the amount of information to be gained from the stimulation of brains of immobile, unconscious subjects is quite limited. In 1896 another German investigator, Paul Peter Ewald, developed a technique in which electrodes were permanently attached to the skull. The electrodes were implanted during a surgical procedure in which the subject was anesthetized; electricity was passed through the electrodes after the subject had fully recovered from the surgery. This new development permitted Ewald to stimulate the brains of fully awake dogs that were restrained only by a leash (Valenstein, 1973). Subcortical brain stimulation became possible following the invention of the stereotaxic instrument. Electrodes were implanted stereotaxically in anesthetized subjects and anchored to their skulls, and electrical stimulation was performed after the subjects regained consciousness. Stimulation of deep brain structures produced behaviors that were strikingly different from those produced by stimulation of the cortex. In the United States much of the pioneering brain stimulation research was conducted in fully awake human subjects in the 1940s and 1950s. Electrical stimulation of subcortical structures was studied in patients with epilepsy, chronic schizophrenia, or movement disorders such as tics and spasticity (Ramey & O’Doherty, 1960). A new stimulation technique, called transcranial magnetic stimulation, is a noninvasive treatment for depression that does not require surgery. With this procedure, magnetic impulses are delivered to the brain via coils that do not touch the head. Transcranial magnetic stimulation permits the investigator to directly stimulate neurons in the cerebral cortex (Wassermann & Zimmermann, 2012). Thus far, it has been used to map functions such as movement, attention, speech, and vision on the cortex. Recording Brain Activity Brain lesioning and stimulation experiments have provided much information about the localization of function in the brain. Another technique, brain recording, has enabled investigators to pinpoint active brain regions in a normally functioning human brain. The earliest brain recordings were conducted by Richard Caton, who was David Ferrier’s classmate in medical school in Scotland (Spillane, 1981). Using a galvanometer, which measures small electrical currents, Caton measured the electrical activity in the brains of rabbits and monkeys while these subjects were exposed to flashing lights, sounds, smells, and tactile stimulation. He noted that the brain’s response varied depending on whether the subject was awake or asleep and that the electrical activity ceased at death. Electroencephalography A 27-year-old woman undergoing an EEG, or electroencephalogram, to monitor the electrical activity of her brain. AJPhoto/Science Source Photo 1.7 Scalp electrodes are the most common items used by EEG investigators. The Austrian psychiatrist Hans Berger is usually credited with the development of electroencephalography (EEG). In 1924, using his young son as his subject, he pasted two pieces of silver foil on his son’s scalp, attached wires to the foil, and connected the wires to a galvanometer. Berger recorded the galvanometer’s response on a roll of paper and observed that his son’s brain emitted a rhythmic electrical signal, which he termed the “alpha rhythm.” The alpha rhythm disappeared whenever his son concentrated on arithmetic problems, demonstrating that these rhythms reflected underlying brain processes. At first, scientists and the general public alike believed that electroencephalography would enable scientists to “read minds.” However, even with great technological advances in the second half of the 20th century, these electrical brain records have not unlocked the secrets of the billions of cells located beneath the skull. First, the electrical signal coming from the brain is very weak, measured in hundred thousandths of volts. Second, most EEG investigators use scalp electrodes (Photo 1.7), which are disks of precious metal, usually gold or platinum, that are positioned on the subject’s scalp. These scalp electrodes pick up signals from millions of brain cells, which makes interpretation of function difficult. Modern EEGs Computer technology has been coupled with electroencephalography to make EEGs more useful to investigators. The computer permits high-speed processing of the recorded electrical activity, which enables investigators to measure brain responses in milliseconds, or thousandths of seconds. In the event-related potential (ERP) procedure, EEG responses are recorded by a computer while a subject performs the same task repeatedly. For example, the subject might be shown patterns of flashing lights and asked to identify the pattern. The computer analysis of the EEGs indicates the timing and location of the brain’s response to the flashing pattern and also the timing and location of brain activity when the subject identifies the pattern. Some brain scientists have used microelectrodes (very tiny electrodes that can be inserted into individual neurons) to record from one neuron at a time. Single-cell recording with microelectrodes has provided investigators with precise information about the function of particular neurons in specific areas of the brain. For example, some cells deep in the brain fire rapidly when cocaine is administered, and others in the same region suppress their activity when cocaine is administered (Pawlak, Tang, Pederson, Wolske, & West, 2009). Magnetoencephalography A woman undergoing a brain scan with a neuromagnetometer, a machine that measures normal electrical brain activity. Hank Morgan/Science Source Photo 1.8 The magnetoencephalography (MEG) technique is used to measure normal electrical brain activity. Magnetoencephalography (MEG) is a relatively new technique, developed by David Cohen in 1968, that enables investigators to measure the magnetic fields generated by active brain cells. Just as an electric current flowing through a wire produces a magnetic field, so do the incredibly small electrical currents generated by neurons also produce tiny magnetic fields. These magnetic fields are measured using a special “captor,” which is lowered over the subject’s head (Photo 1.8). At first, there were great hopes for the applicability of the MEG technique in research and in the clinic. Investigators hailed MEG as much better at localization of brain activity than EEG (Hari & Lounasmaa, 1989). Research by Cohen, the father of MEG, however, demonstrated that MEG is no better at localization than is EEG (Cohen et al., 1990). Like the EEG technique, MEG accurately records brain activity within milliseconds. It is superior to EEG because magnetic fields can pass easily through bone and skin without distortion, and electrical currents cannot. However, like EEG, MEG does not allow precise localization of brain activity. While EEG is capable of measuring electrical signals from the cortex and from the stem regions while MEG cannot pick up signals from deep within the brain, the two imaging techniques provide similar information. One primary difference in the techniques, however, is cost: MEG is very expensive and requires more costly instrumentation (Wendel et al., 2009). Microdialysis Tools of Discovery Experts discuss the technological evolution of studying how the brain functions. What new discoveries have we made with these advances? Neuroscientists employing bottom-up research strategies use specialized recording techniques. One of the most widely used of these techniques is microdialysis, introduced in 1966 (Bito, Davson, Levin, Murray, & Snider, 1966), which involves the sampling of brain chemicals in live, active subjects. Microdialysis, then, is an in vivo technique in which a tube-shaped probe is inserted, with the aid of a stereotaxic instrument, into the region of the brain under investigation. At the tip of the probe is a membrane that allows brain fluid to be drawn up into the tube while a tiny amount of a neutral solution is pumped into the brain. The brain fluid collected by microdialysis is chemically analyzed to determine which substances are present in the brain fluid. Investigators using microdialysis have been able to study chemical activity in the brains of active, freely moving subjects (Rocchitta et al., 2012). One example of an important finding obtained with microdialysis is that reported by Hayley Leitz-Nelson, Juan Dominguez, and Gregory Ball (2010), who studied sex drive in sexually experienced Japanese quails. Dopamine is an important signaling chemical in the brain and is associated with pleasure and motivation. Leitz-Nelson and her colleagues used the microdialysis technique to measure dopamine levels in the brains of male Japanese quails exposed to a sexually receptive female quail that was separated from them by a wire barrier. These investigators found that the male quails that showed an increase in dopamine release in the sexual center of their brains readily copulated with the female when the barrier was removed. However, male quails with low levels of dopamine did not copulate with the sexually receptive female. Thus, the microdialysis technique enabled investigators to demonstrate that dopamine release in the sexual center of the brain is associated with increased sex drive (Leitz-Nelson, Dominguez, & Ball, 2010). 1.6 Brain Imaging Techniques Modern imaging technologies have been developed to enable scientists to measure brain activity. These include single photon emission computed tomography (SPECT), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI). Table 1.2 summarizes the strengths and weaknesses of each brain recording and neuroimaging technique. Computed Tomography CT scan of a patient with Alzheimer’s disease. BSIP/Science Source Photo 1.9 This CT scan of a patient with Alzheimer’s disease shows that the spaces in the center of the brain, called ventricles, are enlarged, and the cerebral cortex has deteriorated. Also known as computerized axial tomography or computer-assisted tomography (CAT), the computed tomography (CT) scan provides three-dimensional images of the brain. Tomography involves passing X-rays through the head at various angles and obtaining a large number of two-dimensional X-ray images or slices, which are then converted into a three-dimensional image by the computer. First introduced in 1973 by South African physicist Allan Cormack and British engineer Sir Godfrey Hounsfield, this method is used to establish links between behavior and specific brain regions (Filler, 2010). If a person is having visual difficulties, for example, and a lesion near the back of the head is detected on the CT scan, we infer that this region of the brain is involved with visual processes. Photo 1.9 is a CT scan of a patient who has Alzheimer’s disease. CT, like all X-ray images, works best for hard tissue, such as bone. The brain is soft tissue and, hence, does not image well with this method. A dye that is radiopaque (that is, a dye that does not allow X-rays to pass through it) is injected into the vein of an individual before a CT scan. The dye is pumped through the blood vessels throughout the entire body and coats the walls of these blood vessels. A CT scan of the brain, then, shows the distribution of blood vessels in the brain. A tumor or other abnormality appears as a disruption in the normal pattern of blood vessels. Single Photon Emission Computed Tomography A brain scan of a patient with Alzheimer’s. Department of Nuclear Medicine, Charing Cross Hospital/Science Source Photo 1.10 This SPECT image from an elderly patient with Alzheimer’s disease shows areas of the cortex as blue or black, indicating areas of reduced brain activity. Single photon emission computed tomography (SPECT) is an extension of the CT technique. In the SPECT technique, the subject is injected with a radioactive isotope that emits single photons, such as an isotope of iodine. The radioisotope is then transported in the bloodstream to the subject’s brain. Because blood flow is increased in active parts of the brain, active regions will contain the highest concentration of photon-emitting isotopes. The location of these emitted photons is detected with a scanner, enabling investigators to measure blood flow in the brain (Photo 1.10). SPECT is useful for localizing brain activity and has, in some cases, been shown to reveal additional statistical significance in contrast to EEGs (Zimmerman, Golla, Paciora, Epstein, & Konopka, 2011). But it has a time lag of more than 20 seconds, much slower than EEG or MEG, and is therefore not very useful for processing cognitive activities, which take fractions of a second to occur. Positron Emission Tomography Many investigators use positron emission tomography (PET) scans in their studies of brain function because the images produced by PET are much more detailed and, hence, provide more information than do SPECT scans. In the PET technique, the subject is injected with a radioactive isotope. A number of radioisotopes, including oxygen and carbon, are used in PET scans, but fluorine is often the most clinically relevant (Lee et al., 2011). Remember that blood flow in the brain is increased in those regions that are most active. This means that active regions contain the most radioactive isotopes and release the most radiation. A detection device is placed around the subject’s head while the subject is performing a task, such as looking at a word or pointing to a stimulus. As the subject participates in the task, certain brain areas become active, and blood flow increases in those areas. Positrons that are emitted from the radioactive isotopes collide with electrons and are annihilated, producing two photons (or gamma rays) that go off in opposite directions and are measured by the detection device. The gamma ray detection device sends the information to a computer, which produces detailed images of the areas of activity in the brain. Studies that use PET technology are producing a wealth of information about how the brain works. More recently, the PET technique has been modified to allow for the study of specific chemicals in the brain (Torigian et al., 2013). We will examine many more applications of PET imaging in behavioral research in later chapters of this book. The information to be gained from PET studies is important, but unfortunately it is an extremely costly technique. For example, the radioactive isotopes used in PET are very expensive to produce. Very few radioactive isotopes release positrons; most release photons, which makes SPECT a cheaper technique to use. Also, using these isotopes puts the subject and experimenter at considerable health risk, and their use is limited by federal guidelines, which does not make repeated trials on the same subject feasible. PET scans are better at localizing brain functions than are SPECT scans because two photons are produced with each positron emitted, making localization more precise. However, like SPECT, PET cannot accurately record the time course of many cognitive activities. It takes minutes to make a PET image, and most cognitive functions occur in less than a second. Functional Magnetic Resonance Imaging Developed in 1990 by Seiji Ogawa and his colleagues at Bell Laboratories, functional magnetic resonance imaging (fMRI) is a measurement technique that is based on conventional magnetic resonance imaging (MRI) technology (Song, 2012). Whereas MRI is used to produce detailed, static images of the brain, fMRI permits measurement of blood flow through a brain region, which is an indicator of activity in that region. The fMRI technique is designed to detect the differences between oxygenated and deoxygenated blood, based on the fact that hemoglobin carrying oxygen has different magnetic properties than deoxygenated hemoglobin. The strange thing about neurons is that they increase their glucose consumption when active, but not their oxygen consumption. This means that when blood flow through an active brain region increases, oxygenated hemoglobin builds up in the blood vessels. Functional MRI detects this increase in blood oxygen and thus is able to pinpoint active brain regions. A brain scan of a 32-year-old woman who had a stroke. Areas are in different colors to show brain damage. Simon Fraser/Science Source Photo 1.11 This is the brain scan of a 32- year-old woman after she had a stroke. The green and blue areas are receiving normal blood flow, while yellow, red, and black are receiving abnormal blood flow. Photo 1.11 is an fMRI image of the brain of a 32-year-old woman after a massive stroke; the image shows the amount of blood flow received by areas of the brain. As you can see, the images produced by fMRI are as detailed as PET scans, and fMRI has many advantages over PET. For example, the fMRI technique is noninvasive and does not require administration of radioactive chemicals, which means that subjects can be tested repeatedly without risk of exposing the subjects to radiation. Functional MRI is also a less expensive technique to use than PET. Moreover, fMRI has a time lag of about 1 second (Stehling, Turner, & Mansfield, 1991), which is far superior to that of PET. EEG and MEG are capable of recording brain activity within milliseconds of its occurrence and, hence, provide a more accurate measure of the time course of brain activity than does fMRI. However, fMRI is much better for localizing a specific function in the brain than are EEG or MEG. One concern when performing fMRI studies is whether or not to compare scanners of different strength levels (Glover et al., 2012). For fMRI experiments, the subject’s entire body must be placed into the scanner, which is shaped like a narrow tube. As a result, some subjects become claustrophobic and uncomfortable during fMRI studies. Any movement by the subject destroys the image being produced, so the subject must lie very still, which increases the subject’s discomfort and renders impossible the study of behaviors involving movement of the head, such as speaking. The type of study conducted in the fMRI scanner is also limited by the high magnetic field in the scanner. For example, the instruments used to present stimuli to subjects in PET studies cannot be used in the magnetic environment of the fMRI scanner. Table 1.2: Comparison of brain recording and brain imaging techniques Technique Benefits Drawbacks EEG Noninvasive; relatively low cost of equipment; accurately records brain activity within milliseconds Difficult to localize exact source of electrical activity; some distortion as electrical currents pass through skull MEG Noninvasive, no distortion as magnetic fields pass through bone; accurately records brain activity within milliseconds Expensive equipment; does not allow precise localization of brain activity; cannot pick up deep signals in the brain SPECT Better than EEG or MEG in localizing brain activity; cheaper than PET imaging Requires administration of a radioisotope; time lag > 20 seconds; cannot be used in studies of cognition PET Better localization of brain activity than SPECT; can be used to localize specific neurotransmitter receptors in the brain Extremely expensive radioisotopes required; some health risk associated with radioisotopes; time lag > 1 min fMRI Noninvasive; precise localization of brain activity; less expensive than PET; time lag < 1 second, better than PET Time lag does not permit study of cognitive processes, subject must remain very still during imaging 1.7 Interpreting the Results of Brain Research When psychologists conduct research, they study qualities or characteristics of organisms that vary. Variable is the name that psychologists give to an element of behavior that is not constant. That is, psychologists study variables associated with behavior, such as age, intelligence, education, or personality. Physiological psychologists study biological variables associated with behavior, such as brain function or brain chemistry. They begin with a hypothesis, or a testable prediction about the relationship between two or more variables, and design a research project that permits them to test whether the predicted relationship between the two variables really exists. For example, in the microdialysis study of sexual behavior in quails (described in the previous section), the investigators examined the relationship between the brain chemical dopamine and sex drive in male quails. Psychological research can be grouped into two categories: experimental research and nonexperimental research. Experimental research involves conducting experiments in which behavior is measured while one or more variables are manipulated and all other variables are held constant or controlled. A variable that is manipulated in an experiment is called an independent variable. In an experiment, the concept of control is most important. All environmental and individual variables (such as room temperature, time of day, or medication level) are strictly controlled in an experiment, and only the independent variables are allowed to vary. One way that psychologists do that is to randomly assign participants to groups. One group, called the experimental group, receives the independent variable, and the other group, called the control group, does not receive the independent variable. By holding the other variables constant while the independent variable is manipulated, we can be certain that only the independent variable is causing any change in the behavior that is observed. Sometimes psychologists cannot control the variables they want to study. For example, if a psychologist was interested in studying the effect of being orphaned on performance in school, that researcher could not randomly assign children to an experimental group and then kill their parents, which would be required in an experiment. Children come to the psychology lab with or without a history of parental loss, and their parental status cannot be controlled. In these situations where variables cannot be controlled, psychologists have to use another research strategy, called nonexperimental research. Correlational Research Nonexperimental research involves collecting data on particular variables without controlling any of the variables. One form of nonexperimental research is called correlational research. Correlational research involves studying the relationship between two or more variables. When conducting correlational research, the psychologist measures one or more variables of interest (for example, age, sex, and a behavioral measure of interest) without trying to control any of the variables. The variables studied in correlational studies already exist and are not manipulated by the researcher. Thus, correlational research cannot tell us about the cause of a behavior but can inform us about the co-occurrence of the variables. Physiological psychologists conduct experiments using brain lesioning and brain stimulation techniques. The investigators manipulate the brain by lesioning or stimulating it in order to study the effects of the manipulation on behavior, while holding all other variables constant. In a brain lesioning experiment, the psychologist will hold other variables (such as age, sex, physical health, body weight, and time of day) constant while performing a brain lesion in one group of rats and no brain lesion in the other group, to study the effect of the lesion on behavior. If the group with the brain lesion shows an impairment in behavior while the nonlesioned group does not, the physiological psychologist can conclude that the brain lesion caused the behavioral impairment. Research that uses brain imaging and brain recording is correlational in nature because the investigator cannot manipulate some variables while holding others constant. In a brain imaging or brain recording study, the investigator compares brain activity in particular groups of individuals (for example, orphaned and non-orphaned children) to determine if there is a difference between the groups. Any differences observed permit the investigator to conclude that a particular brain difference is associated with a particular behavior, but the investigator cannot conclude that the change in brain activity caused the behavior. Correlational studies cannot demonstrate causality because variables that are not controlled can possibly explain the differences observed in the brain recordings. This is demonstrated in the “Case Study” box that discusses the psychological disorder called schizophrenia. Case Study: Schizophrenia and Brain Imaging A PET scan of a normal brain (top) and schizophrenic brain (bottom) showing the increased activity in a schizophrenic brain. Wellcome/Science Source Photo 1.12 This PET scan shows the differences between a normal brain (top) and a schizophrenic brain (bottom). Different areas of the brain are activated when the patient speaks. When she was still in high school, Janelle would sometimes become overwhelmed with a wave of delirious excitement that was accompanied by a feeling that she couldn’t control her thoughts. Soon after that she began to hear voices that seemed to come from the television and radio even when these appliances were turned off. The voices were whispers at first, but they became louder and began to scare her with their intensity and messages. She would lock herself in her bedroom to try to get away from the voices, but she could hear them even with the door shut. Janelle tried to explain what was happening to her parents, but they looked worried when she talked about the voices. Then the voices told her that her parents were evil and planned to execute her. Frightened, Janelle locked herself in her room and refused to answer when her parents called her, instead drawing magical symbols on her bedroom wall that the voices told her would protect her from her parents. Janelle shows many of the classic symptoms of schizophrenia, a severe psychological disorder that will be discussed in detail in Chapter 12. Schizophrenia typically develops in adolescence or early adulthood and is accompanied by disordered thinking, inappropriate emotions, delusions, and hallucinations. Delusions are ideas about oneself that are not grounded in reality. Janelle’s belief that she was in grave danger and that she had magical powers that could protect her are examples of delusional thinking. Hallucinations are perceptions that are not based in realty, and the voices that Janelle was “hearing” were certainly not real. Approximately 7 million people worldwide have been diagnosed with schizophrenia (World Health Organization, 2013), and a great deal of research has been conducted in an attempt to understand this disabling psychological disorder. Unfortunately, researchers have not yet found the cause of schizophrenia, despite decades of intense research. The development of brain imaging technology has provided investigators with a new tool to study schizophrenia (see Photo 1.12). However, because of their correlational nature, brain imaging studies of schizophrenia have done little to move us toward finding the cause of this disorder. That is, brain images of individuals with schizophrenia are collected after the person has developed schizophrenia and cannot tell us how the brain has changed or what caused the change. When brain scans of individuals with schizophrenia are compared to those without schizophrenia, certain differences between their brains are evident. For example, more than 100 published papers have reported enlarged spaces (called ventricles) in the center of the brains of people with schizophrenia, compared to those without the disorder (Ebdrup et al., 2010). Brain images collected from a schizophrenic man and his identical twin who doesn’t have schizophrenia have clearly shown that the ventricles of the schizophrenic man are noticeably larger than those of his unaffected twin. The enlarged ventricles are not the cause of schizophrenia but are correlated with the disorder. Whatever is producing the enlarged ventricles may be causing schizophrenia. Brain imaging research can only give us clues to the relationship between the brain and schizophrenia. Biological Explanations of Behavior All psychologists are concerned with behavior. Some study behavior, and others treat disordered behavior. Some try to explain why particular behaviors occur, and others try to predict or control behavior. When it comes to explaining behavior, there are probably as many explanations as there are branches of psychology. Social, developmental, and personality psychologists may explain behaviors in terms of family history, societal influences, or unconscious conflicts. In this textbook we will focus on biological explanations of behavior. Biological explanations of behavior come in many varieties. Natural selection was one early biological explanation of behavior proposed by Charles Darwin in the late 19th century. According to Darwin’s theory of natural selection, specific traits (including behavioral traits) selectively develop because animals that survive to reproduce have those traits and pass them on to their offspring. For example, bats are animals that sleep during the day and hunt at night for food. Because vision is limited at night, bats have evolved with extremely sophisticated auditory systems that allow them to use echoes to locate prey in the dark. Darwin’s theory of natural selection predicts that those bats that are best able to survive and feed themselves are the individuals that will reproduce most successfully, producing offspring with their echolocation abilities. The American psychologist William James (1842–1910) was extremely influenced by Darwin’s writings. As a result, he introduced the concept of functionalism to explain behavior based on its selective advantage. A functionalist explanation of behavior attempts to identify the survival benefit of a specific behavior to a particular species. For example, investigators who study eating behavior are faced with the perplexing observation that we humans have a large number of neural controls that initiate eating but have few controls that make us stop eating, which encourages obesity. The functionalist explanation for obesity is that humans have survived in environmental niches in which starvation was a way of life (Tounian, 2011). To survive starvation, it is necessary to have controls in place to stimulate eating behaviors, but controls to stop eating are not needed. Therefore, controls to initiate eating developed, and controls to stop eating did not. Other biological explanations of behavior focus on biological properties of an individual, including the individual’s genetic background, structural damage in the brain, or the role of various chemicals in the nervous system. In later chapters we will examine the genetic bases of behavior and behavior disorders. For example, researchers have demonstrated that bipolar affective disorder (Chapter 12) is related to an abnormality on several different chromosomes. Alzheimer’s disease, a particularly devastating disorder that robs an older person of memory, intellect, and personality, has been linked to defects on several chromosomes, including 1, 14, 19, and 21. Another progressive disorder, Huntington’s disease (Chapter 5), which destroys motor and intellectual function, has been linked to an altered gene on chromosome 4. Other authors claim that a variety of widespread disorders, including alcoholism, gambling, drug abuse, binge eating, and attention-deficit disorder, may have a genetic basis (Robbins, Gillan, Smith, De Witt, & Ersche, 2012). In this textbook we will discuss how the organization of the nervous system is related to behavior. We will also look at the effects of physical damage to the nervous system, whether caused by trauma, disease processes, or environmental factors. One example of an environmental factor that affects the brain and, therefore, behavior is exposure to lead. There is ample experimental evidence that lead ingestion is associated with an increase in aggressiveness (Needleman, 2009). We will devote an entire chapter to the effects of brain damage and developmental disorders (Chapter 13). Most importantly, we will concern ourselves with biochemical bases of behavior. We will discuss the roles of many chemical substances in the brain, and we will consider what happens when a person has too much or too little of particular chemicals. These chemicals may be substances manufactured by neurons themselves, or they may be chemicals that a person consumes. For example, cigarette smoking has the effect of decreasing the brain’s supply of a particular enzyme. A decrease in this enzyme will produce an increase in the activity of another brain chemical, dopamine. However, increased dopamine activity is associated with addictive behaviors. This may mean that cigarette smoking becomes addictive because it indirectly increases dopamine activity in the brain (Domino et al., 2013). In this book you will discover that there are all sorts of biological explanations for particular behaviors. These biological factors no doubt interact with social factors, although we will give brief consideration to social factors in this textbook. Our understanding of the relationship between the brain and behavior is growing every day, thanks to the research of behavioral and cognitive neuroscientists. Even as you read this book, important discoveries that will alter the way we view biological influences on behavior in the future are being made. Let’s begin our study of the biological influences on behavior by examining the organization of the nervous system. In Chapter 2, we will examine the nature of neurons and glial cells, the building blocks of the nervous system. To appreciate how the nervous system controls behavior, you must first understand the functions of neurons and glial cells. 1.8 Chapter Summary The History of Brain Research Hippocrates and Galen proposed encephalocentric explanations of behavior that focused on the brain as the chief source of behaviors, thoughts, and feelings. Aristotle supported a cardiocentric theory that regarded the heart as the source of all behavior. In the Western world, cardiocentric theories did not give way to encephalocentric explanations of behavior until the time of Galen in the second century. The modern concept of the brain and brain function did not develop until controlled experiments were conducted in the early 19th century. The earliest investigators of the brain disagreed about whether specific behaviors could be localized to discrete brain structures (localization) or whether the entire brain contributes to any given behavior (holism). Research on the motor cortex in dogs, monkeys, and people supports the concept of localization by showing that the motor cortex is topographically organized in such a way that specific cells in the motor cortex control certain muscles in the body. Studying the Brain and Behavior Many fields of inquiry are concerned with studying the relationship between the brain and behavior, including behavioral and cognitive neuroscience and physiological psychology. Neuroscience is a multidisciplinary approach to studying the brain. Behavioral neuroscience involves bottom-up research strategies that begin by studying the neuron and its interaction with other neurons. Cognitive neuroscience involves top-down research strategies that manipulate cognitive events like problem solving to produce an effect on neural functioning. Physiological psychology is often used interchangeably with behavioral neuroscience. Bottom-up scientific approaches often require the use of nonhuman research subjects. Brain Lesions and Brain Stimulation The earliest techniques used to study the brain and behavior were brain lesioning and stimulation. Lesioning involves disrupting the function of a particular area of the brain. Ablations are typically performed to remove tissue from the cerebral cortex, whereas subcortical lesions are produced by direct current (DC) electricity, radio frequency current, or ionizing radiation. Brain stimulation involves causing a part of the brain to become active and can be accomplished using alternating current (AC) electricity, stimulating chemicals, or transcranial magnetic stimulation. Recording Brain Activity Brain activity can be recorded using electroencephalography (EEG), magnetoencephalography (MEG), single photon emission computed tomography (SPECT), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI). Electroencephalography (EEG) permits recording the electrical activity of the brain. In the event-related potential procedure, the timing and location of brain activity in response to a stimulus are identified. Magnetoencephalography (MEG) permits measuring the magnetic fields generated by active brain cells. Computed tomography (CT) provides three-dimensional images of the brain. Single photon emission computed tomography (SPECT) permits identification of active brain regions by detecting the emission of single photons from an injected radioisotope. Positron emission tomography (PET) provides detailed information about active brain areas, due to the release of positrons by the injected radioisotope used in PET imaging. Functional magnetic resonance imaging (fMRI) permits measurement of blood flow through a brain region, which is an indicator of brain activity in that region. Microdialysis involves sampling brain chemicals in live, active subjects. Biological Explanations of Behavior Natural selection was one early biological explanation of behavior proposed by Charles Darwin in the late 19th century. According to Darwin, specific traits selectively develop in individual species due to a process called natural selection, in which animals that survive to reproduce have traits that ensure survival and pass these traits on to their offspring. The American psychologist William James (1842–1910) introduced the concept of functionalism to explain behavior based on its selective advantage (that is, its survival benefit to a particular species). Other biological explanations of behavior focus on biological properties of an individual, including the individual’s genetic background, structural damage in the brain, or the role of various chemicals in the nervous system. Questions for Thought Name a behavior that might not be controlled by the brain. Design a top-down study and a bottom-up study that would help us understand the relationship between handedness and verbal ability. Under what circumstances should an investigator choose to use nonhuman participants in a study? What techniques might investigators use to study brain changes in Alzheimer’s disease? What is topographical organization, and how was it discovered? Who were the earliest proponents of localization and holism? How are subcortical brain lesions produced? What are the benefits and drawbacks of EEG, MEG, SPECT, PET, and fMRI? Chapter 1 Flashcards Web Links For more information on brain imaging and mapping, visit the Organization for Human Brain Mapping’s website. This professional organization provides numerous resources for learning about brain mapping techniques, the advantages and disadvantages of each, and safety tips when using certain imaging methods. http://www.brainmapping.org/ The American Psychological Association (APA) offers information on how to ethically and responsibly perform research, including the use and care of nonhuman subjects in laboratories. http://www.apa.org/ Key Terms Click on each key term to see the definition. ablation The removal of a part of the brain. behavioral neuroscience A specialized branch of both neuroscience and psychology that involves bottom-up research strategies in which brain function is manipulated and the effect on behavior measured. bottom-up research strategies Research strategies used by behavioral neuroscientists that begin by studying the basic levels of brain function in order to understand higher level functions like thought, attention, and emotion. brain recording A method of studying the brain that enables investigators to pinpoint active brain regions. brain stimulation A method of studying the brain that involves causing a part of the brain to become active. cardiocentric explanations Heart-centered explanations of behavior that posited that the heart produces and regulates all behaviors, including thoughts and emotions; such explanations were popular in ancient civilizations of Western society. cognitive neuroscience A specialized branch of both neuroscience and psychology that involves a top-down approach in which the highest levels of functioning, cognitive events like thinking or problem solving, are manipulated in order to observe the effect on neurons. computed tomography (CT) A recording technique that provides a three-dimensional image of the brain as a result of passing a series of X-rays through the head at various angles. control In an experiment, the concept of control means all environmental and individual variables (such as room temperature, time of day, or medication level) are strictly controlled, and only the independent variables are allowed to vary. correlational research Research that involves studying the relationship between two or more variables by measuring one or more variables of interest without trying to control any of them; such research can inform us about the co-occurrence of variables. craniotomy An incision in the skull. electrode An insulated wire that is used to conduct electricity in brain lesioning or brain stimulation. electroencephalography (EEG) A brain recording technique that measures the electrical activity of the brain. encephalocentric explanations Brain-centered explanations of behavior that came about as a result of dissection studies of human and other animal cadavers in ancient Greece, which led to the discovery of nerves and nerve function. event-related potential (ERP) A measured change in brain activity following the presentation of a stimulus. experiment A method of conducting research that involves measuring behavior while one or more variables are manipulated and all other variables are held constant or controlled. functional magnetic resonance imaging (fMRI) A recording technique that is based on MRI technology and permits localization of accumulation of oxygenated hemoglobin in the brain, which indicates areas of increased brain activity. functionalism A concept introduced by American psychologist William James to explain behavior based on its selective advantage (that is, its survival benefit to a particular species). holism A theory of how the brain divides its labors that holds that every area of the brain is equally capable of controlling all human functions. hypothesis A testable prediction about the relationship between two or more variables. independent variable A variable that is manipulated in an experiment. institutional animal care and use committee (IACUC) A committee composed of scientists and nonscientists that must give approval for all experiments with nonhuman subjects and is also responsible for regularly inspecting animal living quarters and other research areas. lesioning Destroying or disrupting the function of a specific brain structure. localization A theory of how the brain divides its labors that holds that human functions are regulated by distinct, specific areas of the brain. magnetoencephalography (MEG) A technique for studying the brain that enables investigators to measure the magnetic fields generated by active brain cells. microdialysis A technique for sampling chemicals in live, active subjects; it involves inserting a tube-shaped probe into the region of the brain under investigation and collecting brain fluid that is then chemically analyzed to determine which substances are present. microelectrodes Very tiny electrodes that can be inserted into individual neurons. multidisciplinary An approach to studying the brain that involves contributions from several different fields or disciplines, including biologists, chemists, physicists, anatomists, physiologists, psychologists, mathematicians, and engineers. natural selection An early biological explanation of behavior proposed by Charles Darwin in the late 19th century; the theory holds that specific traits, including behavioral traits, selectively develop because animals that survive to reproduce have those traits and pa