Let’s conclude our coverage of motivation by moving down a level of analysis. We’ve just seen how mental contents—needs, goals, and related beliefs—can energize and direct behavior. Let’s now examine brain systems that make it possible for us to experience motivational states. We’ll consider three topics: (1) brain systems that are active during approach and avoidance motivation; (2) cases in which people are too motivated, namely, addictions; and (3) neural systems that enable people to set goals that guide their behavior.

We’ve said throughout this chapter that motivational forces are diverse. Yet there is a simple distinction—between approach and avoidance motivation—that simplifies the diversity.

Approach motivation refers to a broad class of motives that concern the growth and enhancement of an organism (Harmon-Jones, 2011). Efforts to obtain food or attain a higher social status are both cases of approach motivation. Avoidance motivation is a drive to protect the self against threats and dangers. Staying away from physical threats (e.g., a dark alley that looks dangerous) and from social threats (e.g., a party where you might embarrass yourself socially) are both cases of avoidance motivation. A number of the specific motives and motivational orientations we encountered earlier in the chapter (e.g., needs to achieve and to avoid failure; or motivational orientations involving promotion or prevention) can be seen as relating to one of the two motivations, approach or avoidance.

The approach/avoidance distinction is psychological; it claims that approach and avoidance are psychologically distinct states. Are they also biologically distinct? In other words, are there distinct systems in the brain that correspond to these distinct types of motivation?

Much theory and research suggests that there are. A theoretical framework developed by British scientist Jeffrey Gray (reviewed in Smillie, Pickering, & Jackson, 2006) is useful for thinking about motivation and the brain. Gray conducted research on animals. In laboratory studies, they were exposed to stimuli that signaled the later occurrence of either rewards (which the animal would be inclined to approach) or punishments (which the animal would want to avoid). Gray then explored the brain systems when the two types of signals were presented. Based on this research, he distinguished between a behavioral approach system and a behavioral inhibition system. Both systems can be understood in terms of two types of biological mechanisms—the neurotransmitters that activate the systems, and the exact brain anatomy that is activated, as we’ll see now.

BEHAVIORAL APPROACH SYSTEM. Stimuli that signal the future presence of rewards activate a behavioral approach system. The behavioral approach system is a neural system that arouses an organism, energizing it to seek out rewarding stimuli (e.g., food).

The neurotransmittiter dopamine is the biochemical key to this reward system. Although there is some disagreement on its precise functions, dopamine is known to be released when an organism encounters reward signals, and to activate brain regions needed for pursuing those rewards (Pickering & Corr, 2008).

Regarding the anatomy of this system—that is, the exact neural structures within the brain that are involved—the key mechanisms are in lower regions of the brain: the brain stem and limbic system. Dopamine travels along a bundle of nerve fibers, the medial forebrain bundle, to a set of neurons that is central to the pursuit of rewards, the nucleus accumbens (Wise, 1998; Figure 11.10). Many see this overall system of biochemistry and neural anatomy as a reward system in the brain (e.g., Makris et al., 2008), that is, a system dedicated to producing the pleasurable and motivating states that drive organisms to pursue rewarding stimuli.

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BEHAVIORAL INHIBITION SYSTEM. Signals of punishment activate a behavioral inhibition system. The behavioral inhibition system is a neural system within the brain that increases levels of arousal and feelings of anxiety. Activation of this system causes organisms to stop pursuing rewards and to attend, instead, to environmental threats. The behavioral inhibition system is activated by stimuli that signal punishment, by novel stimuli that could be threatening, and by stimuli that innately trigger fear.

Both the biochemistry and the anatomy of the behavioral inhibition system differ from those of the approach system. In terms of the biochemistry, the most important neurotransmitter is not dopamine but serotonin (Graeff, 2004). Anatomically, the key neural systems are located in the hippocampus and the amygdala (Barrós-Loscertales et al., 2006; Gray & McNaughton, 2000).

The biological differences between the systems are consistent with the psychological distinctions you learned earlier. Time and again, psychologists proposed that motives to attain positive outcomes and to avoid harms and threats were psychologically distinct. Brain research reveals that they are distinct biologically, too.

Brain research with humans provides further evidence of these distinctions, while also widening the scope of brain mechanisms involved. In addition to the lower-level brain regions that we share with animals, higher-level regions that are uniquely human are involved. These include biological matter in the front of the brain, that is, the frontal cortex. Findings indicate that different sides of the frontal cortex—the left and right hemispheres of the brain (see Chapter 3)—play different roles. The left side is more strongly involved in approach motivation, whereas the right side is more strongly involved in avoidance (Harmon-Jones, 2011).

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Sometimes people are too motivated. They incessantly seek out substances or behaviors that are attractive, but ultimately harmful. These are people who suffer from addictions. Addictions are psychological disorders in which people use a drug or engage in an activity repeatedly and uncontrollably (Goldman, Oroszi, & Ducci, 2005).

Addictions are costly to individuals and to society as a whole. At a personal level, substance abuse can ruin friendships, romantic relationships, and family life. In economic terms, the cost of addictions is staggering: an estimated $600 billion a year in the United States in health-, crime-, and productivity-related costs (National Institute on Drug Abuse, 2012). Addictions also are costly to society’s cultural life. The careers of numerous great musicians and artists have been cut short by drug abuse.

Why are so many people so prone to develop addictions? Addictive substances tap into a neural system found in everyone’s brain: the reward system (behavioral approach system) described in the preceding section. A wide variety of addictive substances activate the brain circuitry that normally becomes active during rewarding, pleasurable experiences (Wise, 1998).

Addictive substances affect the reward system by increasing dopamine activity. Different substances increase dopamine in different ways. For example, nicotine increases the amount of dopamine released into the spaces between neurons (Stahl, 2002). Cocaine blocks a molecular process in which previously released dopamine is taken back into brain cells (Nestler, 2006; Figure 11.11). Either way, activity in the reward center of the brain increases.

Furthermore, addictive substances create two long-lasting changes in the brain that make it particularly difficult for people to break an addictive habit (Koob & Le Moal, 2005). First, they reduce the normal functioning of the brain’s reward system. As a result, naturally occurring events become less rewarding and people lose motivation for everyday activities. Second, they increase the activity of brain systems that produce emotionally negative withdrawal states when a person’s levels of an addictive substance are low.

Evidence indicates that the addictive behaviors have an effect on the brain that is similar to that of addictive substances. For instance, gambling—a behavior that becomes addictive for millions of people—has been shown to activate the same reward center that is activated by addictive drugs (Holden, 2001). When researchers study the brains of pathological gamblers and addictive drug users, they find similar patterns of response; regions of the brain involved in the processing of reward are particularly active in response to both drugs and monetary cues (Clark et al., 2013).

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Goals shape motivation. This simple sentence captures a main theme of research on motivation and the mind. Research on motivation and the brain is beginning to shed light on the biological mechanisms that make it possible for people to formulate personal goals.

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Psychologically, goals have two key features: (1) thoughts about the future and (2) thoughts that a person cares about. Goals, then, are not simple statements of fact (e.g., “Someday my hair will be gray”). They represent future states that one values (e.g., “Someday I will earn a college degree”). Because goals have more than one aspect psychologically, you might expect that more than one brain region will be involved in goal processing.

To study the neural basis of people’s thoughts about goals, researchers (D’Argembeau et al., 2010) first asked participants to think of some future possibilities that were personal goals for them, and some other possible future events that they might experience but that were not personal goals. Later, they used a brain scanner to create images of regions of the brain that were highly active while participants were thinking about their personal goals, future activities that were not personal goals, and also some routine activities such as taking a shower.

Consistent with what one would expect from a psychological analysis of goals, two different brain regions—not just one region—were active during goal processing (D’Argembeau et al., 2010; Figure 11.12). One region, the posterior cingulate cortex, is known to be active when people contemplate future events. The other, the ventral medial prefrontal cortex, is involved in computing value, that is, the degree to which a piece of information is valuable to oneself. Input from these two neural systems—a future events system and a personal value system—combines to produce the representation of personal goals. Future research on goal setting and the brain is sure to provide more insight into the biological mechanisms that enable people to motivate themselves (Figure 11.13).