Past life regression is a technique that uses hypnosis to recover what practitioners believe are memories of past lives or incarnations, though others regard them as fantasies or delusions or a type of confabulation. Past-life regression is typically undertaken either in pursuit of a spiritual experience, or in a psychotherapeutic setting. Most advocates loosely adhere to beliefs about reincarnation, though religious traditions that incorporate reincarnation generally do not include the idea of repressed memories of past lives.
The technique used during past-life regression involves the subject answering a series of questions while hypnotized to reveal identity and events of alleged past lives, a method similar to that used in recovered memory therapy and one that similarly misrepresents memory as a faithful recording of previous events rather than a constructed set of recollections. The use of hypnosis and suggestive questions can tend to leave the subject particularly likely to hold distorted or false memories. The source of the memories is more likely cryptomnesia and confabulations that combine experiences, knowledge, imagination and suggestion or guidance from the hypnotist than recall of a previous existence. Once created, the memories are indistinguishable from memories based on events that occurred during the subject's life. Memories reported during past-life regression have been investigated, and revealed historical inaccuracies that are easily explained through a basic knowledge of history, elements of popular culture or books that discuss historical events. Experiments with subjects undergoing past-life regression indicate that a belief in reincarnation and suggestions by the hypnotist are the two most important factors regarding the contents of memories reported.
In ancient Indian literature, the Upanishads mention past-life regression, but the Yoga Sutras of Patañjali discuss the concept in greater detail. Written during the 2nd century BC, the Hindu scholar Patañjali discussed the idea of the soul becoming burdened with an accumulation of impressions as part of the karma from previous lives. Patañjali called the process of past-life regression prati-prasav (literally "reverse birthing"), and saw it as addressing current problems through memories of past lives. Some types of yoga continue to use prati-prasav as a practice.