Post-traumatic amnesia is a state of confusion or memory loss that occurs immediately following a traumatic brain injury. 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.
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|Studies of traumatic brain injury cases show that less than 3% experienced no memory loss at all.|
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.
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. In some cases, anterograde amnesia may not develop until several hours after the injury.
Post-traumatic amnesia may be either short term, or longer-lasting (often over a month – see box at right), but is hardly ever permanent. When continuous memory returns, the person can usually function normally. Retrograde amnesia sufferers may partially regain memory later, but memories are never regained with anterograde amnesia because they were not encoded properly.
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. 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.