One of the defining characteristics of advanced organisms is the ability to make flexible, yet adaptive responses to environmental stimuli. These stimuli may arise from within the organism or impinge upon it from the outside. The resulting myriad of stimuli ranges in salience from the barely noticeable to the intense. The stimuli in the intense range are usually considered to be biologically significant, whether they originate within the organism or are encountered in the outside environment.

At any given moment, the organism is likely to be faced with many stimuli that could be acted upon, but in reality only a few become the targets of behavior. Psychologists have conceptualized this process as a system of drives and rewards. The particular combination of stimuli that arises from the outside world and from the physiology of the organism triggers brain activity that has two major effects: It energizes behavior and directs behavior. For example, if an individual has gone for several hours without food, the stimuli arising from inside the body produce an effect which can be labeled hunger. These stimuli may be intensified by external cues such as the position of the hands on a clock, a television advertisement for junk food, or other food related items. There will be an increase in activity, and, given the appropriate circumstances, this activity will be directed toward food items. The consumption of food is said to be rewarding, and reduces the stimuli that initially energized the search for food.

The schema outlined above reflects the operation of the reward system, and as discussed in previous chapters, this system is believed to rely upon activity of catecholamines in fibers that arise from cells in the midbrain and project to various forebrain regions. Normally, this system organizes behavior in a systematic fashion that not only enhances the organisms ability to survive, but also makes it easier for psychologists to formulate laws of behavior. When this system fails to operate normally, the behavior of the affected individual strays outside of the normal expectancies, and some sort of label is attached to indicate a problem in behavioral adjustment. The behavior of the individual may be energized at inappropriate times (or at an inappropriate level), or it may be directed toward goal objects that are inappropriate or even nonexistent. Let us consider a couple of examples before going into the main body of this chapter.

One of the behavioral disorders that has been linked to the reward system both in its symptoms and its treatment is hyperkinesis or hyperactivity. This disorder typically appears in early childhood and is considerably more likely to afflict boys than girls. These children rarely require institutionalized care, but present tremendous challenges to teachers and parents. The disorder is characterized by impressive and unceasing physical activity. The child typically begins the day early with loud interactions with parents and siblings, running through the house, bumping into things and breaking them, getting into fights, spilling food, and so on. In school, the child distracts others by refusing to stay seated, fails to complete projects, and generally performs poorly. Bedtime is no exception to the exaggerated activity, and several tuckings in are likely to be required before both child and caretaker collapse into sleep.

When placed in the context of the reward system outlined above, hyperkinesis certainly can be viewed as an increase in the energizing aspect of drives, but it might also be characterized as a lack of directed behavior. Indeed, the disorder is now officially referred to as attention deficit disorder. It is in this regard that one of the most paradoxical and effective treatments comes into the scene. The behavior of these children would seem to require no further stimulation, yet one of the most effective treatments is the administration of amphetamines. The amphetamines are known to facilitate the functioning of neurons that release catecholamines, and have been shown to enhance rewards or to serve as rewards themselves. The most popular interpretation of the effectiveness of amphetamines in treating hyperkinesis is that the treatment enhances reward and provides more direction to the behavior. In both hyperkinetic and normal children (and adults for that matter), amphetamines can increase the attention span, which tends to normalize the behavior of the hyperkinetic children (e.g., Zahn, et al, 1980).

Autism is another disorder that may involve a dysfunction of the reward system, although the links have been less direct than in the case of hyperkinesis. The disorder is characterized by withdrawal from other individuals and a failure to respond to many external stimuli. Stereotyped behaviors are common,

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Behavioral Disorders And Environmental Stimuli. (April 3, 2021). Retrieved from