Studies in traumatic amnesia.

Retrograde amnesia is for a period of time, usually for a fraction of a minute in simple concussion, and not loss of memory for an event. The length of time for which there is no recollection is not directly related to the duration of coma but can be for days or even weeks. It is characterized by inability of restoration of memory for the period in question. Any retrograde amnesia of more than a day's duration results from trauma only if the trauma is severe enough to cause prolonged coma, usually weeks. It should be under suspicion of being due pathologically to more than concussion. Careful attention should be given to the possibility of hysteria or malingering as a factor.