His early findings, which were based on observations from LSD research, uncovered four major types of experiences that, according to Grof, correspond to levels in the human unconscious: (1) Abstract and aesthetic experiences; (2) Psychodynamic experiences; (3) Perinatal experiences; (4) Transpersonal experiences. Grof returns to many of these findings in later books. Psychodynamic levels, which correspond to the theory of Sigmund Freud, is the area of biographical memories, emotional problems, unresolved conflicts and fantasies. Perinatal levels, which correspond to the theories of Otto Rank, is the area of physical pain and agony, dying and death, biological birth, aging, disease and decrepitude. Transpersonal levels, corresponding to the theories of C.G. Jung, is the area of a number of spiritual, paranormal and transcendental experiences, including ESP phenomena, ego transcendence and other states of expanded consciousness. In order to bring structure to the psychodynamic and perinatal levels Grof introduces two governing systems, or organizing principles: The COEX-system, which is the governing system for the psychodynamic level, and the Basic Perinatal Matrices, which represent the birthing stages and is the governing system for the perinatal level.