I believe it can be caused by mild to moderate epilepsy, as some members have talked about. If you scroll down there's this current thread:
http://www.dpselfhelp.com/forum/index.php?/topic/71906-my-brain-scan-results-for-dpdr-interesting/
http://www.dpselfhelp.com/forum/index.php?/topic/71906-my-brain-scan-results-for-dpdr-interesting/