Based on the passage below, what do scientologists believe cause neuroses and mental problems?

Scientology texts say that a human possesses an immortal inner self, termed a thetan, that resides in the physical body and has experienced many past lives. Scientologists believe that traumatic events experienced by the thetan over its lifetimes have resulted in negative "engrams" forming in the mind, causing neuroses and mental problems. They claim that the practice of auditing can remove these engrams; Scientology groups charge fees for clients undergoing auditing. Once an auditing practitioner deems the engrams to have been removed, an individual is given the status of "clear". They can take part in a further series of activities that are termed "Operating Thetan" (OT) levels, which require further payments.

Scientologists believe that neuroses and mental problems are caused by traumatic events experienced in past lives. These traumatic experiences result in negative "engrams" forming in the mind.