nerve cells in the body that are not part of the central nervous system. The PNS includes the
The nervous system is an amazing network, responsible for everything we think, feel, or do. It is divided into two functional units: the central nervous system (CNS), which consists of the spinal cord and brain, and the peripheral nervous system (PNS), which consists of all the other nerve cells in the body.The two systems are anatom-ically separate, but their functions are highly interdependent. The PNS transmits a variety of information to the CNS, which organizes and evaluates that informa-tion and then directs the PNS to perform specific behaviours or make bodily adjustments. The discussion below first considers the CNS, focusing on the rela-tion between the brain and psychological funcrela-tion.
Consider the human brain’s complexity.The first animals’ nervous systems were probably little more than a few specialized cells with the capacity for electrical sig-naling. An adult human brain today weighs approximately 1.4 kilograms and has the consistency of a soft-boiled egg.The brain is best viewed as a collection of inter-acting neural circuits that have accumulated and developed throughout human
M E A S U R I N G U P
1. Neurons communicate by firing. Put the following steps in the correct order so they describe this process.
a. The presynaptic neuron “reuptakes” the neurotransmitter from the synapse.
b. If the receptors allow a sufficient excess of excitatory neurotransmitters into the cell, the postsynaptic neuron will respond by opening its sodium and potassium gates.
c. Neurotransmitters bind with receptors on the postsynaptic neuron’s dendrites.
d. Excitatory and inhibitory messages are compared in the cell body of the postsynaptic neuron.
e. Neurotransmitters are released into the synapse by a presynaptic neuron.
f. The charge inside the cell goes from negative to positive.
g. The gates open in succession as the information is passed along the axon away from the cell body and toward the terminal buttons.
h. The sodium and potassium gates close, and the neuron returns to its resting potential.
2. Match each major neurotransmitter with its major functions.
The major functions are
evolution. Through the process of adapting to the environment, the brain has evolved specialized mechanisms to regulate breathing, food intake, sexual behav-iour, and bodily fluids, as well as sensory systems to aid in navigation and assist in recognizing friends and foes. Everything we are and do is accomplished by the brain and, for more rudimentary actions, the spinal cord. Early in life, overabundant con-nections form among the brain’s neurons; subsequently, life experiences help
“prune” some of these connections to strengthen the rest.
The brain’s basic structures and their functions enable us to accomplish feats such as seeing, hearing, remembering, and interacting with others. Understanding these relationships also helps us understand psychological disorders. As we learn more about the brain, however, we must avoid jumping to conclusions about brain/behaviour relationships that are not warranted by the data.
THE BRAIN: A BRIEF HISTORY OF UNDERSTANDING ITS FUNCTIONS Psychological scientists have learned a great deal of what they know about the functioning of different brain regions through the careful study of people whose brains have been damaged by disease or injury. Perhaps the most famous historical example of brain damage is the case of Phineas Gage. In 1848, Gage was a 25-year-old foreman on the construction of Vermont’s Rutland and Burlington Railroad. One day, he dropped his tamping iron on a rock, igniting some blasting powder. The resulting explosion drove the iron rod—about a metre long and two and a half centimetres in diameter—into his cheek, through his frontal lobes, and clear out through the top of his head (FIGURE 3.21). Gage was still conscious as he was hurried back to town on a cart. Able to walk, with assistance, upstairs to his hotel bed, he wryly remarked to the awaiting physician,
“Doctor, here is business enough for you,” and said he expected to return to work in a few days. In fact, Gage lapsed into unconsciousness and remained unconscious for two weeks. Afterward, his condition steadily improved, and he recovered remarkably well, at least physically.
Unfortunately, Gage’s accident led to major personality changes. Whereas the old Gage had been regarded by his employers as “the most efficient and capable”
of workers, the new Gage was not. As one of his doctors later wrote, “The equi-librium or balance, so to speak, between his intellectual faculties and animal
FIGURE 3.21 Phineas Gage As discussed below, analysis of Gage’s damaged skull pro-vided the basis for the first modern theories of the prefrontal cortex’s role in both personality and self-control. (a) This photo shows Gage’s death mask next to his skull. (b) This computer-generated image reconstructs the rod’s probable path into the skull.
(b) (a)
propensities seems to have been destroyed. He is fitful, irreverent, indulging at times in the grossest profanity, . . . impatient of restraint or advice when it conflicts with his desires. . . . A child in his intellectual capacity and manifestations, he has the animal passions of a strong man.” In summary, Gage was “no longer Gage.”
Unable to get his foreman’s job back, Gage exhibited himself in various New England towns and at the New York Museum (owned by P. T. Barnum), worked at the stables of the Hanover Inn at Dartmouth College, and drove coaches and tended horses in Chile. After a decade, his health began to decline, and in 1860 he started having epileptic seizures and died within a few months. Gage’s recovery was initially used to argue that the entire brain works uniformly and that the healthy parts of Gage’s brain had taken over the damaged parts’ work. However, the med-ical community eventually recognized that Gage’s psychologmed-ical impairments had been severe and that some areas of the brain in fact have specific functions. Gage’s case provided the basis for the first modern theories of the role of a part of the brain called the prefrontal cortex in personality and self-control. Reconstruction of Gage’s injury through examination of his skull has made it clear that the pre-frontal cortex was the area most damaged by the tamping rod (Damasio, Grabowski, Frank, Galaburda, & Damasio, 1994). Recent studies of patients with similar injuries reveal that this brain region is particularly concerned with social phenomena, such as following social norms, understanding what other people are thinking, and feel-ing emotionally connected to others. People with damage to this region do not typically have problems with memory or general knowledge, but they often have profound disturbances in their ability to get along with others.
The brain was not always recognized as the mind’s home.The ancient Egyptians, for example, viewed the heart as more important; they elaborately embalmed each dead person’s heart, which was to be weighed in the afterlife to determine the deceased’s fate.The person’s brain, however, they simply threw away. But in the fol-lowing centuries, especially among the Greeks and Romans, recognition grew that the brain was essential for normal mental functioning. Much of this change came from observing people with brain injuries. At least since the time of the Roman gladiators, it was clear that a blow to the head often produced disturbances in men-tal activity, such as unconsciousness or the loss of speech.
By the beginning of the nineteenth century, anatomists understood the brain’s basic structure reasonably well. But debates raged over how the brain produced mental activity. Did different parts do different things? Or were all areas of the brain equally important in cognitive activities such as problem solving and memory (an idea called equipotentiality)? In Germany in the early nineteenth century, the neu-roscientist Franz Gall and his assistant, the physician Johann Spurzheim, proposed their theory of phrenology, based on the idea that the brain operates through func-tional localization. Phrenology is the practice of assessing personality traits and men-tal abilities by measuring bumps on the human skull. The theory of phrenology was so popular that in the 1930s an enterprising company manufactured 33 Psychographs. Psychographs were devices used to tell about participants’ person-alities based on the locations and sizes of bumps on their heads.That these machines were popular at state fairs and amusement parks suggests few people, if any, took the personality readings seriously (FIGURE 3.22).
Although phrenology was an influential theory in its day because it was based on the seemingly scientific principle that brain functions were localized, its validity could not be tested scientifically. Taking this general idea of localization, the American behavioural psychologist Karl Lashley set out to identify the places in the brain where learning occurred. Lashley believed that specific brain regions (namely, parts of the cortex—discussed below) were involved in motor control and
FIGURE 3.22 Phrenology and the Psychograph (a) In the early nineteenth cen-tury, Johann Spurzheim created phrenological maps of the skull, including this one, where each numbered region corresponds to a differ-ent characteristic. (b) Psychographs, such as the one depicted here, were marketed as being able to “do the work of a psychoanalyst” by showing “your talents, abilities, strong and weak traits, without prejudice or flattery.”
(b) (a)
sensory experiences, but that all other parts of the brain contributed equally to men-tal abilities.Today, Lashley’s theory has been largely discredited, and we now know that the brain consists of a patchwork of highly specialized areas.
The first strong evidence that the brain regions perform specialized functions came from the work of the French physician and anatomist Paul Broca (Finger, 1994). In 1861, Broca performed an autopsy on his patient Monsieur Leborgne.
Before his death, Leborgne had lost the ability to say anything other than the word tan but could still understand language.When he examined Leborgne’s brain, Broca found substantial damage to the front left side, caused by a large lesion.This obser-vation led him to conclude that this particular region was important for speech.
Broca’s theory has survived the test of time.This left frontal region became known as Broca’s area,and it has since been repeatedly confirmed to be crucial for the pro-duction of language (FIGURE 3.23). In 1934,Wilder Penfield, of McGill University, became the first director of the world-renowned Montreal Neurological Institute, which remains at the forefront of neuroscience research. Penfield’s studies helped develop cures for epilepsy and also mapped out the sensory and motor responses that occurred when specific brain regions were stimulated (discussed further in Chapter 5,“Sensation and Perception”). Penfield’s mapping work showed the clear specificity of psychological functioning for distinct brain regions.
The debate over whether psychological processes are located in specific parts of the brain or distributed throughout the brain continued so long, in part, because until fairly recently researchers have not had methods for studying ongoing men-tal activity in the working brain. The invention of brain imaging methods in the late 1980s changed that situation swiftly and dramatically. Since then, research has exploded, cutting across various levels of analysis, linking specific brain areas with particular behaviours and mental processes. The new imaging techniques have advanced our understanding of the human brain the way the development of tel-escopes advanced our understanding of astronomy—and the brain’s structures and functions may be as complex as distant galaxies. Although philosophers have long debated what it means to be conscious of something, psychological scientists now examine, even measure, consciousness and other mental states that were previously viewed as too subjective to be studied.
Broca’s area The left frontal region of the brain, crucial for the production of language.
Broca’s area
(a) (b)
FIGURE 3.23 Broca’s Area (a) Paul Broca studied Monsieur Leborgne’s brain and identified the lesioned area as crucial for speech production. (b) This illustration shows the location of Broca’s area.
Brain region Related function also explore how the mind is adaptive, one of this text’s seven major themes.