There is an article on Wikipedia discussing past life regression.
A general scientific explanation of beliefs about past lives is that:
the memories are the result of
cryptomnesia, narratives created by the subconscious mind using
imagination, forgotten information and suggestions from the
therapist. Memories created under hypnosis
are indistinguishable from actual memories and can be more vivid than
factual memories. The greatest predictor of individuals
reporting memories of past lives appears to be their beliefs about the
existence in reincarnation - individuals who believe in reincarnation
are more likely to report such memories, while sceptics or
disbelievers are less so.
The study discussed in Spanos (1996) sounds particularly relevant to understanding the nature of such past life beliefs. To continue quoting the Wikpedia article:
Spanos' research leads him to the conclusion that past lives are not
memories, but actually social constructions based on patients acting
"as if" they were someone else, but with significant flaws that would
not be expected of actual memories. To create these memories, Spanos'
subjects drew upon the expectations established by authority figures
and information outside of the experiment such as television, novels,
life experiences and their own desires.
Thus, past life regression therapy is invalid in the sense that patients are not actually recalling past lives. Nonetheless, there still remains a question of whether it offers therapeutic benefits. Meaning, purpose, and self-esteem are all important human needs. For therapists and patients who believe in past lives, fleshing out past lives could potentially help to fulfil such needs. That said, I don't know of any scientific studies that have evaluated such therapy. Such therapy also raises a number of ethical issues in terms of fostering illusions in the client.
- Spanos NP (1996). Multiple Identities & False Memories: A Sociocognitive Perspective. American Psychological Association (APA). pp. 135–40. ISBN 1-55798-340-2.