The issue of whether memories can be repressed is controversial, to say the least. Some research indicates that memories of traumatic events, most commonly childhood sexual abuse, may be forgotten and later spontaneously recovered. However, whether these memories are actively repressed or forgotten due to natural processes is unclear.

Support for the Existence of Repressed Memories

In one study where victims of documented child abuse were re-interviewed many years later as adults, a high proportion of the women denied any memory of the abuse. Some speculate that survivors of childhood sexual abuse may repress the memories to cope with the traumatic experience. In cases where the perpetrator of the abuse is the child's caretaker, the child may push the memories out of awareness so that he or she can maintain an attachment to the person on whom they are dependent for survival.

Traumatic memories are encoded differently than memories of ordinary experiences. In traumatic memories, there is a narrowed attentional focus on certain aspects of the memory, usually those that involved the most heightened emotional arousal. For instance, when remembering a traumatic event, individuals are most likely to remember how scared they felt, the image of having a gun held to their head, or other details that are highly emotionally charged. The limbic system is the part of the brain that is in charge of giving emotional significance to sensory inputs; however, the limbic system (particularly one of its components, the hippocampus) is also important to the storage and retrieval of long-term memories. Supporters of the existence of repressed memories hypothesize that because the hippocampus is sensitive to stress hormones and because the limbic system is heavily occupied with the emotions of the event, the memory-encoding functionality may be limited during traumatic events. The end result is that the memory is encoded as an affective (i.e., relating to or influenced by the emotions) and sensory imprint, rather than a memory that includes a full account of what happened. In this way, traumatic experiences appear to be qualitatively different from those of non-traumatic events, and, as a result, they are more difficult to remember accurately.

Psychological disorders exist that could cause the repression of memories. Psychogenic amnesia, or dissociative amnesia, is a memory disorder characterized by sudden autobiographical memory loss, said to occur for a period of time ranging from hours to years. More recently, dissociative amnesia has been defined as a dissociative disorder characterized by gaps in memory of personal information, especially of traumatic events. These gaps involve an inability to recall personal information, usually of a traumatic or stressful nature. In a change from the DSM-IV to the DSM-5, dissociative fugue is now classified as a type of dissociative amnesia. Psychogenic amnesia is distinguished from organic amnesia in that it is supposed to result from a nonorganic cause; no structural brain damage or brain lesion should be evident, but some form of psychological stress should precipitate the amnesia. However, psychogenic amnesia as a memory disorder is controversial.

Opposition to the Existence of Repressed Memories

Memories of events are always a mix of factual traces of sensory information overlaid with emotions, mingled with interpretation and filled in with imaginings. Thus, there is always skepticism about the factual validity of memories.

There is considerable evidence that, rather than being pushed out of consciousness, traumatic memories are, for many people, intrusive and unforgettable. Given research showing how unreliable memory is, it is possible that any attempt to "recover" a repressed memory runs the risk of implanting false memories. Researchers who are skeptical of the idea of recovered memories note how susceptible memory is to various manipulations that can be used to implant false memories (sometimes called "pseudomemories").

A classic study in memory research conducted by Elizabeth Loftus became widely known as the "lost in the mall" experiment. In this study, subjects were given a booklet containing three accounts of real childhood events written by family members and a fourth account of a fictitious event of being lost in a shopping mall. A quarter of the subjects reported remembering the fictitious event, and elaborated on it with extensive circumstantial details. 

"Lost in the mall" experiment

Some of the early research in memory conformity involved the "lost in the mall" technique.

While this experiment does show that false memories can be implanted in some subjects, it cannot be generalized to say that all recovered memories are false memories. Nevertheless, these studies prompted public and professional concern about recovered-memory therapy for sexual abuse. According to the American Psychiatric Association, "most leaders in the field agree that although it is a rare occurrence, a memory of early childhood abuse that has been forgotten can be remembered later. However, these leaders also agree that it is possible to construct convincing pseudomemories for events that never occurred. The mechanism(s) by which both of these phenomena happen are not well understood and, at this point it is impossible, without other corroborative evidence, to distinguish a true memory from a false one."