A variety of injuries of illnesses can lead to a loss of memory, or amnesia. Some forms of amnesia are retrograde, meaning that they disrupt memory for things learned prior to the event that initiated the amnesia. Retrograde amnesia is often cased, for example, by blows to the head. Other forms of amnesia have the reverse effect, causing dirsuption for experiences after the onset of amnesia (anterograde amnesia).
Korsakoff's syndrome: There is typically little problem in remembering events that took place before the onset of alcoholism. Current topics can also be maintained in the mind as long as there is no interruption. New information, though, is displaced from the mind, is seemingly lost forever.