Recent symptom provocation neuroimaging studies of people with PTSD provide a neurobiological explanation for these clinical observations. During the provocation of traumatic memories there was decreased activation of Broca's area, the part of the CNS most involved in the translation of subjective experience into speech. Simultaneously, the areas in the right hemisphere that are thought to process intense emotions and visual images had significantly increased activation (Rauch and others). These observations have given rise to the notion that traumatic memories may be encoded differently than memories for ordinary events, probably because extreme emotional arousal interferes with interpretive and associative systems in the CNS (van der Kolk 1997).
The question of whether the sensory perceptions reported by people with PTSD are accurate representations of the sensory imprints at the time of the trauma is intriguing. Studies of flashbulb memories have shown that the relationship between emotionality, vividness and confidence is very complex, and does not necessarily reflect accuracy. Once sensations are transcribed into a personal narrative, they become subject to the laws that govern explicit memory: to become a socially communicable story that is subject to condensation, embellishment and contamination. Thus, while trauma may leave indelible sensory and affective imprints, once these are incorporated into a personal narrative, this, like all explicit memory, is subject to varying degrees of distortion (Southwick and coworkers).
The DSM-IV recognizes that trauma can lead to extremes of retention and forgetting. Traumatized individuals often suffer from a combination of vivid recall for some elements of the trauma and amnesias for others. While the vivid intrusions of traumatic images and sensations are the most dramatic expressions of PTSD, the loss or absence of recollections for traumatic experiences is well-documented. This is specifically recognized in the DSM-IV as dissociative amnesia, "a reversible memory impairment in which memories of a personal experience cannot be retrieved in a verbal form."
The issue of traumatic amnesia was first recognized by the founder of neurology, Jean Martin Charcot (1887), and has been frequently documented since. For example, after the evacuation from Dunkirk during World War II, Sargeant and Slater (1941) reported that 144 of 1,000 consecutive admissions to a field hospital were amnestic for the experience.
As long as men were found to suffer from delayed recall of exposure to terror under clearly identifiable circumstances, this issue was comfortably incorporated in the canon of the profession. However, when the same memory problems started to be documented in girls and women, some of whom started to seek justice against their alleged perpetrators, the issue became a highly emotional one and largely moved from the arena of science into journalism and the courtroom. There the adversarial process, with its polarized legal arguments, has promoted selective attention to one-sided arguments, rather than to the complexity of the issues involved.
The degree to which mainstream culture itself can ignore reality is illustrated by the fact that as recently as 1982, the Veterans Affairs Department rejected a grant application because "it has not been shown that PTSD is relevant to the mission of the VA." Today, we know that over a million men who served in Vietnam still suffer from PTSD.
The 1980 edition of Friedman, Sadock and Kaplan's Textbook of Psychiatry III estimated that incest occurred in less than one out of a million women. In 1993 the U.S. Department of Health and Human Services estimated 217,700 new cases of child sexual abuse. Hence, the prevailing culture may be as vulnerable to distortions of reality as psychiatric patients themselves.