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.
Yukio Ishizuka
In 1976, while many psychiatrists continued to be preoccupied with the definition of psychological illnesses (Diagnostic Statistical Manuals), Ishizuka turned to a monograph by M. Jahoda published in 1958 entitled « Current Concepts of Positive Mental Health.» Jahoda offered six conditions for developing and evaluating future models of Positive Mental Health. In doing so, she pointed out the limits of the ‘disease’ model and set guidelines to define models of health applicable both in wellness and disease. 
Concluding that the ‘medical’ or ‘disease model’ used in psychiatry was not fit to understand healthy human beings or to assist them in ‘normal’ or optimal functioning, Ishizuka began to build such a model. His exposure to the East, and training in the West helped him develop a model of health across different cultures. Focusing almost entirely on the experience of his diverse patients, he challenged what he knew to define a model of health and personality applicable both in extreme distress and optimal health.