In recent years, the studies of the effects of drugs on the behavior of animals have been playing an increasingly important role. Animal studies have… - Thaddeus E. Weckowicz

When one turns to psychological models of mental illness, one finds that the psychodynamic model of human mind and of mental disease is also of considerable antiquity. Thus, Empedocles of Agrigentum (490-430 B.C.) from whom Hippocrates took the theory of four elements, stressed the importance of emotions of love and hate as the controlling agents of human behavior and of physiological functions.

Von Bertalanffy also studied the works of , a neo-Platonist Renaissance philosopher, on whom he wrote a book. Cusanus, who had a lasting influence on von Bertalanffy, may be regarded as a precursor of general systems theory. Nicholas of Cusa rejected Aristotelianism dominant in theology and philosophy at the end of the middle ages and adopted neo-Platonist ideas and even went back to the philosophy of , a pre-Socratic philosopher. Anaxogoras said that 'everything was everything else.' Therefore all categories of thinking were relative and all contradictions only apparent. According to Cusanus the knowledge of infinite God cannot be grasped by human mind it can only be approached from different directions. The idea of God has many aspects which appear to be contradictory. It is similar to a human face which may present different appearances when perceived from different perspectives.

There are several definitions of Depersonalization, which are really descriptions of the symptom. The one offered by Schilder (1914) is perhaps most clear and precise. It is given here in a free English translation: The individual feels totally different from his previous being; he does not recognise himself as a person. His actions seem automatic, he behaves as if he were an observer of his own actions. The outside world appears to him strange and new and it has lost the character if reality. The self does not behave any longer in its former way." From this definition it can be seen that the core of the symptom is a change in appearance, a "strangeness" of the object of experience: either the self or the external world or both. There is also a disturbance in the subject-object relationship producing perplexity and interfering with the smooth flow of conscious experience. These aspects of depersonalization are stressed in one form or another by all the investigators of this phenomenon.