6.1 General Principles of Motivation

To motivate, in the most general sense of the term, is to set in motion. In psychology, the term motivation is often used to refer to the entire constellation of factors, some inside the organism and some outside, that cause an individual to behave in a particular way at a particular time. Defined this way, motivation is a very broad concept—almost as broad as all of psychology. Every chapter in this book deals with one facet of motivation or another. Genes, learning, physiological variables, perceptual and thought processes, developmental variables, social experiences, and personality characteristics can all play a part in motivation.

© The New Yorker Collection, 2004, Glen LeLievre, from cartoonbank.com. All Rights Reserved.

A more precise label for the specific topic of our present discussion is motivational state, or drive. These terms are used interchangeably to denote an internal condition that orients an individual toward a specific category of goals and that can change over time in a reversible way (the drive can increase and then decrease). Different drives direct a person toward different goals. Hunger orients one toward food, sex toward sexual gratification, curiosity toward novel stimuli, and so on.

Drives in psychology are generally thought of as hypothetical constructs. The psychologist does not observe a state of hunger, thirst, or curiosity inside the animal but infers the existence of that state from the animal’s behavior. An animal is said to be hungry if it behaves in ways that bring it closer to food, to be sexually motivated if it behaves in ways that bring it into contact with a sexual partner, and to be curious if it seeks out and explores new environments. To say that the drive varies over time is to say that the animal will work harder, or accept more discomfort, to attain the goal at some times than at others. The assumption is that something inside the animal changes, causing it to behave differently, at different times in the same environment.

But the inside interacts constantly with the outside. Motivated behavior is directed toward incentives, the sought-after objects or ends that exist in the external environment. Incentives are also called reinforcers (the term used in Chapter 4), rewards, or goals. The motivational state that leads you to stand in line at the cafeteria is presumably hunger, but the incentive for doing so is the hamburger you intend to purchase. Drives and incentives complement one another in the control of behavior; if one is weak, the other must be strong to motivate the goal-directed action. Thus, if you know that the cafeteria’s hamburger tastes like cardboard (weak incentive), you are likely to wait in line for it only if your hunger drive is strong; but if the cafeteria serves a really great hamburger (strong incentive), you are likely to wait even if your hunger drive is weak.

Drives and incentives not only complement each other but also influence each other’s strength. A strong drive can enhance the attractiveness (incentive value) of a particular object: If you are very hungry, even a hamburger that tastes like cardboard might seem quite attractive. Conversely, a strong incentive can strengthen a drive: The savory aroma of a broiling hamburger wafting your way as you wait in line might increase your hunger drive, which might in turn induce you to eat something that previously wouldn’t have interested you if, by the time you get to the grill, all the hamburgers are gone.

Varieties of Drives

In general, drives motivate us toward goals that promote our survival and reproduction. Some drives promote survival by helping us maintain the internal bodily conditions that are essential for life.

Drives That Help Preserve Homeostasis

In a now classic book entitled The Wisdom of the Body (1932/1963), the physiologist Walter B. Cannon described simply and elegantly the requirements of the tissues of the human body. For life to be sustained, certain substances and characteristics within the body must be kept within a restricted range, going neither above nor below certain levels. These include body temperature, oxygen, minerals, water, and energy-producing food molecules. Physiological processes, such as digestion and respiration, must continually work toward achieving what Cannon termed homeostasis [ho'-me-o-sta′-sos], the constancy of internal conditions that the body must actively maintain. Most relevant for psychology, Cannon pointed out that maintaining homeostasis involves the organism’s outward behavior as well as its internal processes. To stay alive, individuals must find and consume foods, salts, and water and must maintain their body temperature through such means as finding shelter. Cannon theorized that the basic physiological underpinning for some drives is a loss of homeostasis, which acts on the nervous system to induce behavior designed to correct the imbalance.

Following Cannon, psychologists and physiologists performed experiments showing that animals indeed do behave in accordance with the needs of their bodily tissues (Woods & Stricker, 2012). For example, if the caloric (energy) content of its food is increased or decreased, an animal will compensate by eating less or more of it, keeping the daily intake of calories relatively constant. As another example, removal of the adrenal glands causes an animal to lose too much salt in its urine (because one of the adrenal hormones is essential for conserving salt). This loss of salt dramatically increases the animal’s drive to seek out and eat extra salt, which keeps the animal alive as long as salt is available (Stricker, 1973; Stricker & Verbalis, 2012).

The force of homeostasis in human behavior was dramatically and poignantly illustrated by the clinical case of a boy, referred to as D. W., who when 1 year old developed a great craving for salt (Wilkins & Richter, 1940). His favorite foods were salted crackers, pretzels, potato chips, olives, and pickles; he would also take salt directly from the shaker. When salt was denied him, he would cry until his parents gave in, and when he learned to speak, salt was one of his first and favorite words. D. W. survived until the age of 3½, when he was hospitalized for other symptoms and placed on a standard hospital diet. The hospital staff would not yield to his demands for salt, and he died within a few days. An autopsy revealed that his adrenal glands were deficient; only then did D. W.’s doctors realize that his salt craving came from physiological need. His strong drive for salt and his ability to manipulate his parents into supplying it, even though they were unaware that he needed it, had kept D. W. alive for more than 2 years after the onset of the adrenal deficiency—powerful evidence for “the wisdom of the body.”

Limitations of Homeostasis: Regulatory and Nonregulatory Drives

Homeostasis is a useful concept for understanding hunger, thirst, and the drives for salt, oxygen, and an appropriate body temperature, but not for understanding many other drives. Consider sex, for example. People are highly motivated to engage in sex, and sex serves an obvious evolutionary function, but there is no tissue need for it. No vital bodily substance is affected by engaging in sexual behavior; nobody can die from lack of sex (despite what an overly amorous admirer may have told you). Psychologists therefore find it useful to distinguish between two general classes of drives—regulatory and nonregulatory. A regulatory drive is one, like hunger, that helps preserve homeostasis, and a nonregulatory drive is one, like sex, that serves some other purpose.

A Functional Classification of Mammalian Drives

One way to think about the whole set of drives that we share with other mammals is to categorize them in accordance with their evolutionary functions—their roles in promoting survival and reproduction. From an evolutionary perspective, it is useful to distinguish among the following five categories of mammalian drives:

1. Regulatory drives. As already noted, these are drives that promote survival by helping to maintain the body’s homeostasis. Hunger and thirst are prime examples.
2. Safety drives. These are drives that motivate an animal to avoid, escape, or fend off dangers such as precipices, predators, or enemies. The most obvious safety drive is fear, which motivates individuals to flee from danger. Another is anger, which is manifested when fighting (or threatening to fight) rather than flight is needed to ensure one’s safety. We will argue later in this chapter that sleep is also a safety drive. It evolved at least partly as a means of keeping animals tucked quietly away during that part of each 24-hour day when they would be most in danger if they were moving about.
3. Reproductive drives. The most obvious of these are the sexual drive and the drive to care for young once they are born. When they are at a peak, these drives can be extraordinarily powerful. Animals (including people) will risk their lives to mate and to protect their offspring. As discussed in Chapter 3, sexual jealousy, including the anger associated with it, also serves the function of reproduction to the degree that it promotes the fidelity of one’s sexual partner.
4. Social drives. Many mammals, and especially humans, require the cooperation of others to survive. The social drives include the drives for friendship and for acceptance and approval by the social groups of which one is a part. In humans, these drives can be as powerful as the regulatory, safety, and reproductive drives. People will risk their lives for friendship and for social approval.
5. Educative drives. These consist primarily of the drives to play and to explore (curiosity). As discussed in Chapter 4, the young of nearly all social mammals practice life-sustaining skills through play, and mammals of all ages acquire useful information about their environment by exploring novel objects and territories. When other drives are not too pressing, the drives for play and exploration come to the fore.

Human Drives That Seem Not to Promote Survival or Reproduction

Not all of human motivation is easily understood in terms of survival and reproduction. For instance, humans everywhere like to produce and experience art, music, and literature (including oral stories and poetry). What motivates these activities? Have we evolved special aesthetic drives? If so, what adaptive functions prompted the natural selection of such drives?

Early art We have no idea whether or not the person who produced this drawing—about 18,000 years ago in one of the Lascaux Caves, in France—had a concept of art or a word for it. To the modern eye, however, this is a work of art. It may represent a universal human proclivity.

Serge de Sazo/Photo Researchers, Inc.

At present, these questions are much debated, and there is no firm answer. Our own view is that the pursuits of art, music, and literature are natural extensions of our drives for play and exploration. These pursuits can exercise perceptual and motor skills, imagination, and creative thinking in ways that may be useful in future real-life situations and can also provide us with ideas for governing our own lives. Like other playful and exploratory activities, these pursuits help our minds to grow during periods when there are no more pressing survival needs that must be fulfilled. Developing skills in art, music, and storytelling may also enhance one’s status in a social group and impress members of the opposite sex, which would have had survival value for our ancestors.

A somewhat different (but not incompatible) view, presented by Steven Pinker (1997), is that art, music, and literature appeal to us not because we have special drives for them but because they tap into many of our already existing drives and proclivities, which evolved for other purposes. For example, in describing the appeal of fiction, Pinker (1997) writes: “When we are absorbed in a book or movie, we get to see breathtaking landscapes, hobnob with important people, fall in love with ravishing men and women, protect loved ones, attain impossible goals, and defeat wicked enemies” (p. 539). In this example, a book or movie appeals to our drives for sex, love, social esteem, parenting, achievement, and aggression. To suggest that art, music, and literature may be vicarious means of satisfying other drives rather than drives in and of themselves is not to diminish them. These pursuits enrich our lives immensely; they extend us beyond evolution’s narrow dictates of mere survival and reproduction.

Of course, some things that people become motivated for are truly harmful. Drug addictions and compulsive gambling are artificial drives, created by human inventions, which can ruin people’s lives. How these tap artificially into our natural drive mechanisms is a topic to which we shall return soon.

Drives as States of the Brain

We said that drives are normally considered to be hypothetical entities, inferred from observed behavior. Yet, essentially all psychologists would agree that drives are products of physical processes within the body, particularly within the brain. In theory, at least, every drive that we experience corresponds with some state of the brain.

According to the central-state theory of drives, which will guide much of the discussion in this chapter, different drives correspond to neural activity in different sets of neurons in the brain. A set of neurons in which activity constitutes a drive is called a central drive system. Although the central drive systems for different drives must be at least partly different from one another, they may have overlapping components. For example, because hunger and sex are different drives, the neural circuits for them cannot be identical. If they were, hunger and sex would always occur in tandem; the drives would always rise and fall together. Their respective circuits may, however, share components that produce behavioral effects common to both drives, such as increased alertness.

What characteristics must a set of neurons have to serve as a central drive system? First, it must receive and integrate the various signals that can raise or lower the drive state. For hunger, these signals include chemicals in the blood, the presence or absence of food in the stomach, and the sight and smell of food in the environment. Second, a central drive system must act on all the neural processes that would be involved in carrying out the motivated behavior. It must direct perceptual mechanisms toward stimuli related to the goal, cognitive mechanisms toward working out strategies to achieve the goal, and motor mechanisms toward producing the appropriate movements. Refer back to Figure 5.24 (p. 176), which depicts a hierarchical model of the control of action, with mechanisms involved in motivation and planning at the top. The central drive systems are part of that top level of the hierarchy. To affect behavior (for example, to cause a hungry person to cross a room for some fresh cherries), they must influence the activity of motor systems at lower levels of the hierarchy.

Researchers have sound reasons to believe that the hypothalamus is the hub of many central drive systems. Anatomically, this brain structure is ideally located to play such a role (see Figure 6.1). It is centered at the base of the brain, just above the brainstem, and is strongly interconnected with higher areas of the brain. It also has direct connections to nerves that carry input from, and autonomic motor output to, the body’s internal organs. It has many capillaries and is more sensitive to hormones and other substances carried by the blood than are other brain areas. Finally, through its connections to the pituitary gland, it controls the release of many hormones (as described in Chapter 5). Thus, the hypothalamus has all the inputs and outputs that central drive systems would be expected to have. And, as you will see later in the chapter, small disruptions in particular parts of the hypothalamus can have dramatic effects on an animal’s drives.

Figure 6.1: Location of the hypothalamus The hypothalamus is ideally situated to serve as a hub for central drive systems. It has strong connections to the brainstem below, the limbic system and cerebral cortex above, and the endocrine system (by way of its tie to the pituitary gland).