<P> Behavioral theories of depression explain the etiology of depression based on the behavioural sciences, and they form the basis for behavioral therapies for depression . </P> <P> Depression is a significant mental illness with physiological and psychological consequences, including sluggishness, diminished interest and pleasure, and disturbances in sleep and appetite . It is predicted that by the year 2030, depression will be the number one cause of disability in the United States and other high - income countries . </P> <P> Behavioral theories of depression emphasize the role maladaptive actions play in the onset and maintenance of depression . These theories stem from work concerning the principles of learning and conditioning from the early to mid-1900s . Ivan Pavlov and B.F. Skinner are often credited with the establishment of behavioral psychology with their research on classical conditioning and operant conditioning, respectively . Collectively, their research established that certain behaviors could be learned or unlearned, and these theories have been applied in a variety of contexts, including abnormal psychology . Theories specifically applied to depression emphasize the reactions individuals have to their environment and how they develop adaptive or maladaptive coping strategies . </P> <P> Behavioral activation (BA) is an idiographic and functional approach to depression . It argues that people with depression act in ways that maintain their depression and locates the origin of depressive episodes in the environment . While BA theories do not deny biological factors that contribute to depression, they assert that it is ultimately the combination of a stressful event in an individual's life and their reaction to the event that produces a depressive episode . Individuals with depression may display socially aversive behaviors, fail to engage in enjoyable activities, ruminate on their problems, or engage in other maladaptive activities . According to BA theory, these behaviors most often function as avoidance mechanisms while the individual tries to cope with a stressful life event, resulting in a decrease in positive reinforcers or perceived control . Rumination is particularly important in the onset of depression . There are two main coping mechanisms, rumination and distraction . Ruminators spend time focusing on the stressful event and their feelings, while distractors engage in activities that distance them from the event and their feelings . Ruminators are much more likely to become depressed than distractors . </P>

Who was one of the first theorists to emphasize the role of thought in depression
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