Most cases of dissociative amnesia are temporary, but memory gaps can last anywhere from a few minutes to an entire lifetime. When a person with generalized dissociative amnesia forgets everything about the self and their life, they may move to a new location and establish a new identity but, when discovered, they don’t know how they got there or why they have no identification. A person with dissociative amnesia may not remember friends, family members, or coworkers. Symptoms range from forgetting personal information, like one’s own name and address, to blocking out specific traumatic events or even the events of one’s entire life. There is also some evidence that traumatic stress events can actually lead to a long-term physical reduction of the volume of the brain's hippocampus, an organ integrally involved in the making and processing of memories.Dissociative amnesia is not normal forgetting, like misplacing keys or forgetting the name of someone you met once or twice. Memories from just before the trauma are often completely lost, partly due to the psychological repression of unpleasant memories (psychogenic amnesia), and partly because memories may be incompletely encoded if the event interrupts the normal process of transfer from short-term to long-term memory. The most obvious symptom is the loss of memory for the present time.

Retrograde amnesia sufferers may partially regain memory later, but memories are never regained with anterograde amnesia because they were not encoded properly. What are the symptoms of post-traumatic amnesia (PTA). When continuous memory returns, the person can usually function normally. Post-traumatic amnesia may be either short term, or longer-lasting (often over a month - see box at right), but is hardly ever permanent. Retrograde amnesia refers to the inability to recall events which occurred immediately prior to head trauma or other acute brain insult. In some cases, anterograde amnesia may not develop until several hours after the injury. The person has no continuous memory of day-to-day events, and recent events may be equally affected, so that they are unable to. The amnesia resulting from trauma may be retrograde amnesia (loss of memories that were formed shortly before the injury, particularly where there is damage to the frontal or anterior temporal regions) or anterograde amnesia (problems with creating new memories after the injury has taken place), or both. Post-traumatic amnesia (PTA) is the time after a period of unconsciousness when the injured person is conscious and awake, but is behaving or talking in a bizarre or uncharacteristic manner. The extent of amnesia varies, but most commonly involves memories of recent traumatic or stressful events. Typically the victim suffers two types of memory defect: retrograde amnesia, forgetting pretrauma events, and anterograde amnesia, not retaining what’s happening now. 'Dissociative amnesia is characterized by an inability to recall important autobiographical memories, where recall would be expected and is inconsistent with ordinary forgetting. In 6% of cases, post-traumatic amnesia lasted for less than an hour 7% experienced memory loss from an hour to a day 16% between a day and a week 23% between a week and a month and 45% experienced amnesia for longer than a month. Amnesia following violent but nonpenetrating head trauma, known in the business as closed-head injury, is common and reasonably well understood. Inability to recall key features of the traumatic event (usually dissociative amnesia not due to head injury, alcohol or drugs) (C3 in DSM-IV) Criterion D continues on next slide. Studies of traumatic brain injury cases show that less than 3% experienced no memory loss at all. The injured person is disoriented and unable to remember events that occur after the injury and may be unable to state their name, where they are, and what time it is, etc.

Post-traumatic amnesia is a state of confusion or memory loss that occurs immediately following a traumatic brain injury.

Amnesia from trauma