Retrograde amnesia is the memory loss of events that occurred after the onset of amnesia.

Retrograde amnesia is the memory loss of events which occured after the onset of amnesia. 

This statement is somewhat false, but also true. With retrograde amnesia we're referring to the memory loss of events which occured shortly before a certain traumatic event which caused amnesia but also could include  events shortly after the amnesia.

Anterograde amnesia on the other hand refers to the inability to remember events and form new memories following a traumatic event.

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