“As an undergraduate student in psychology, I was taught that multiple personalities were a very rare and bizarre disorder. That is all that I was taught on ... It soon became apparent that what I had been taught was simply not true. Not only was I meeting people with multiplicity; these individuals entering my life were normal human beings with much to offer. They were simply people who had endured more than their share of pain in this life and were struggling to make sense of it.”
― Deborah Bray Haddock, The Dissociative Identity Disorder Sourcebook
The terms repressed and recovered memories at their broadest refer to memories that were inaccessible until something allowed them to again be retrieved. More specifically, the term "repressed memory" usually refers to the inability to consciously recall a traumatic memory, and the term "recovered memory" refers to a traumatic memory that was repressed but is now again accessible.
Repressed memories are also referred to as dissociated memories. According to the theory of structural dissociation, dissociated memories are memories that are contained within one or more emotional parts (EP) and so are inaccessible to one or more apparently normal parts (ANP). Memories become dissociated because their integration into the whole of the self would threaten the self's ability to function and survive. Intrusions of dissociated memories cause activation of positive posttraumatic stress disorder (PTSD) symptoms, reinforcing avoidance.
Another theory for the existence of repressed and recovered memories is the theory of betrayal trauma. Betrayal trauma refers to any trauma in which trust or well-being is significantly violated by people or institutions on which the victim relies for survival. Severe betrayal trauma can result in betrayal blindness, the unawareness or forgetting of the victim regarding the trauma. At a simple level, betrayal blindness can occur in response to adultery or societal inequalities as the victimized individual seeks to preserve existing relationships, institutions, or social systems upon which their well-being depends. At a more complex level, a child may become blind to the betrayal of parental abuse because to acknowledge and react to the abuse in a normal fashion would be to threaten the child's attachment to their parent and so threaten their access to food, shelter, protection, emotional support, or other factors necessary for the child's physical and mental survival. Such a reaction is more likely to be produced when the perpetrator of the betrayal is a caregiver to the victim or when high levels of fear result. It has been shown that high levels of betrayal trauma predict PTSD symptoms and dissociation better than does fear alone (Freyd, 2012).1
Another theory that affects repressed memories is the theory of shareability. The idea behind this theory is that childhood abuse often does not allow for communication regarding this abuse and that non-shared memories of abuse may be more implicit than explicit, procedural than declarative, perceptual than language based, and continuous than categorical, though communicating about the event may change this. Memories that are not shareable may be not particularly consciously accessible (Freyd, 2005).2
One mechanism for repressed memories may be state dependent learning. Norepinephrine has been linked with flashbacks in individuals with chronic PTSD and so may play a role in activating specific states, such as trauma-oriented states, in structurally dissociated individuals. That is, acute stress that leads to norepinephrine release may be what's needed to activate an emotional part (Nijenhuis, Hart, & Steele, 2010)3, and the traumatic memories may be contained within this dissociated part. State dependent learning has also been linked to different neural conditions during memory formation. One study on fear conditioning in mice found that fear conditioning associations and memories seemed to be only accessible in the physiological state in which the fear conditioning occurred (Jovasevic et al., 2015)4. According to Marla Paul, memories can be encoded and stored in completely different neuronal circuits even on a genetic level when the memories are made under different neural states, and this may be what allows some traumatic memories to be inaccessible under normal conditions (2015)5. More information on state dependent learning and its potential role in PTSD, dissociative disorders, and repressed memories can be found here.
According to Kenneth S. Pope, "reports of recovered memories of child sex abuse may be described as the result of implanting, false memory syndrome, repression, dissociation, motivated forgetting, directed forgetting, amnesia, betrayal trauma, retroactive inhibition, suggestion, self-induced hypnotic trance states, personality disorder, thought suppression, retrieval inhibition, cognitive gating, or biological protective processes" (1998).6 Terms used to describe repression include "dissociative amnesia, repression, dissociative state, traumatic amnesia, psychogenic shock, or motivated forgetting" (Dallam, n.d.).7
There is controversy regarding the validity of recovered memories. Despite this, there is no support for the idea that recovered memories are any less accurate than continuous memories. The continuity of memories and the validity of memories are two different factors. All memories are to some degree influenced by personal interpretation, and one may forget something previously remembered or think that they had previously remembered more than they actually had. The issue is also complicated because memory can be explicitly unavailable yet implicitly expressed through behavior (Freyd, 2012).8
Often, when repressed memories are doubted, this doubt is associated with the idea of false memory syndrome (FMS) which is further associated with the Satanic Ritual Abuse Panic of the 1980s and 1990s. However, FMS is not recognized by the American Psychiatric Association though both the DSM-5 and ICD-10 include dissociative amnesia. While it is true that not all recovered memories are accurate, there is no reason to assume that none are accurate. There is a good deal of evidence supporting that at least some recovered memories are valid.
Factors that may increase the likelihood of memories being repressed are: the nature of the traumatic event; the age at which the trauma occurred, with young victims being more likely to rely on repression; whether the trauma happened only once (car crash, stranger rape, witnessing a murder) or was repeated (spousal abuse, child abuse, political torture, combat), with repeated or long-term traumas being more likely to lead to repression; whether the trauma was caused by an accident or natural disaster or whether it was a betrayal trauma, with the latter being more likely to lead to repression, especially in the case of the perpetrator being a caregiver to a child; whether the victim was coerced or explicitly threatened into silence; whether the abuse was sporadically combined with periods of non-abuse ("honeymoon periods"); isolation during abuse; a caregiver giving "alternate reality statements" (blaming the victim, denying that anything happened, denying that what happened was wrong) (Dallam, n.d.).7
1 Freyd, J. J. (2012). What is a betrayal trauma? What is betrayal trauma theory? Retrieved May 1, 2015, from http://dynamic.uoregon.edu/jjf/defineBT.html
2 Freyd, J. J. (2005). What is shareability? Retrieved May 1, 2015, from http://dynamic.uoregon.edu/jjf/defineshareability.html
3 Nijenhuis, E.R.S., Van der Hart, O., & Steele, K. (2010). Trauma-related structural dissociation of the personality. Activitas Nervosa Superior, 52(1), 1-23.
4 Jovasevic, V., Corcoran, K. A., Leaderbrand, K., Yamawaki, N., Guedea, A. L., Chen, H. J., . . . Radulovic, J. (2015). GABAergic mechanisms regulated by miR-33 encode state-dependent fear. Natural Neuroscience, 18(9), 1265–1271. doi:10.1038/nn.4084
5 Paul, M. (2015). How traumatic memories hide in the brain, and how to retrieve them. Northwestern. Retrieved from http://www.northwestern.edu/newscenter/stories/2015/08/traumatic-memories-hide-retrieve-them.html
6 Pope, K. S. (1998). Pseudoscience, cross-examination, and scientific evidence in the recovered memory controversy. Psychology, Public Policy, and Law, 4(4), 1160-1181. doi:10.1037/1076-89188.8.131.520
7 Dallam, S. (n.d.). Questions and answers regarding dissociative amnesia. Retrieved May 2, 2015, from http://www.leadershipcouncil.org/1/tm/amnesia.html
8 Freyd, J. J. (2012). What about recovered memories? Retrieved May 1, 2015, from http://dynamic.uoregon.edu/jjf/whatabout.html