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Motivational States Influence Goal-Directed Behavior

ONE DAY A CHEETAH, TAKING REFUGE from the mid-day sun in the shade of a tree, views a distant antelope with apparent indifference. Later in the afternoon, the sighting of the antelope provokes immediate orienting and stalking behavior. The stimulus is the same, but the behavioral responses are very different. What has changed is the motivational state of the animal.

Motivational states influence attentiveness, goal selection, investment of effort in the pursuit of goals, and responsiveness to stimuli. They thus drive approach, avoidance, and action selection. This chapter focuses on the neurobiological basis of motivational states related to rewards and the manner in which reward-related brain circuits are implicated in mechanisms underlying drug addiction.

Both Internal and External Stimuli Contribute to Motivational States

Motivational states reflect one’s desires, and desires can be influenced by physiological status as well as by stimuli that predict future rewarding and aversive events. Motivational states thus depend on both internal and external variables. Internal variables include physiological signals concerning hunger or thirst, as well as variables related to the circadian clock. For example, the frequency and duration of foraging vary with the time of day, the time since an animal has last eaten, and whether, if female, she is lactating.

Other internal variables are related to cognitive processes. In the game of blackjack, for instance, being dealt the same card in different hands can cause a player to go bust or make 21, leading to very different emotional responses and adjustments in subsequent decision making and action selection. The differential meaning of the same stimulus (a particular card) is made possible by the cognitive understanding of the rules of the game of blackjack. The cognitive understanding of a rule is an internal variable. Similarly, different social situations often elicit distinct behavioral responses to the same stimulus, such as whether one chugs wine at a college party or sips it at a formal dinner.

External variables also influence motivational states. These variables include rewarding incentive stimuli. For example, when a dehydrated cheetah comes across a watering hole during a search for antelopes, the sight of the water may serve as an incentive stimulus, tipping the balance between hunger and thirst and driving the animal to interrupt its quest for food to drink. However, an internal variable—the state of the cheetah’s hydration—can also lead to a different reward value being assigned to the same sensory stimulus, the watering hole. Even innately rewarding stimuli, such as a sweet tastant that normally elicits pleasure, can in some circumstances become unpleasurable. Chocolate cake may be innately rewarding to chocolate lovers, but satiation to the chocolate—which involves modulation of an internal variable—can decrease the reward value of this stimulus and thereby affect motivational state.

Rewards Can Meet Both Regulatory and Nonregulatory Needs on Short and Long ...

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