Reactive attachment disorder
The broad theoretical framework for current versions of RAD is attachment theory, based on work conducted from the 1940s to the 1980s by John Bowlby, Mary Ainsworth and René Spitz. Attachment theory is a framework that employs psychological, ethological and evolutionary concepts to explain social behaviors typical of young children. Attachment theory focuses on the tendency of infants or children to "seek proximity" to a "particular attachment figure" (familiar caregiver), in situations of alarm or distress, behavior which appears to have survival value. This is known as a discriminatory or selective attachment. Subsequently, the child begins to use the caregiver as a base of security from which to explore the environment, returning periodically to the familiar person. Attachment is not the same as love and/or affection although they are often associated. Attachment and attachment behaviors tend to develop between the ages of six months and three years. Infants become attached to adults who are sensitive and responsive in social interactions with the infant, and who remain as consistent caregivers for some time. Caregiver responses lead to the development of patterns of attachment, that in turn lead to internal working models which will guide the individual's feelings, thoughts, and expectations in later relationships. For a diagnosis of reactive attachment disorder, the child's history and atypical social behavior must suggest the absence of formation of a discriminatory or selective attachment.
Marc David Lewis
Through a sabbatical at the University of Oregon in 2000-2001, Lewis took the next step in developing his integrated model by delving into the neural underpinnings of emotion regulation. His current research program tests this model by examining brain and behavior in normal and clinically referred children and assessing neural changes corresponding with successful treatment. His papers on the contribution of dynamic systems theory and affective neuroscience to understanding human development and clinical syndromes have appeared in journals such as "Child Development", "Behavioral and Brain Sciences", "Development and Psychopathology", and "Perspectives on Psychological Science". He has also co-authored two books with his wife, Dr. Isabela Granic. The first is an edited volume of dynamic systems approaches to emotional development. The second is a guide for parents about when to attempt sleep training with toddlers. 
Dr. Lewis' most recent book, "Memoirs of an Addicted Brain", is an account of his addiction to drugs as a young man with accompanying explanations of the neurobiological processes underlying various drug experiences as well as the process of addiction itself.