Amnesia is the loss of memory. (Loftus, 1990. p.393) Amnesia may be either permanent or temporary. Amnesia can result from brain injury, shock, fatigue, repression, or illness. ("How your brain remembers." , 2000) Some drugs can also cause temporary amnesia.

Anterograde Amnesia is the inability to remember events (episodic memory) that occurred after trauma. The individual has difficulty learning new information (semantic memory). However, implicit memory is usually preserved. If one suffers solely from anterograde amnesia, his or her memories of events prior to the brain trauma will remain intact. (Benjamin, Hopkins, & Nation, 1994. p.281) (Loftus, 1990. p.393) (Scoville & Milner, 1957; Corkin, 1984 MIT) (Benjamin, Hopkins, & Nation, 1994. p.282)

Retrograde Amnesia is the inability to remember events that happened before a trauma. (Loftus, 1990.p.393), (Benjamin, Hopkins, & Nation, 1994. p.281)This time period may stretch from a few minutes to several years, and typically it is worst for events which occurred just before the injury.

Very rarely does someone experience retrograde amnesia as a result of a physical brain injury without also experiencing anterograde amnesia. In this case, the individual will have near total loss of memory for events occurring after the injury, and some loss of memory for events which occurred before the injury.