Repressed memory is a controversial and largely discredited psychiatric phenomenon characterized by an inability to recall autobiographical information, usually of a traumatic or stressful nature. The concept originated in psychoanalytic theory, where repression is understood as a defense mechanism that excludes painful experiences and unacceptable impulses from consciousness. Repressed memory is presently considered largely unsupported by research. Sigmund Freud initially claimed the memories of historical childhood trauma could be repressed while still unconsciously influencing present behavior and emotional responses. He later revised this belief.