What's the difference between anterograde and retrograde amnesia?

After vs before. Anterograde amnesia is difficulty remembering things since the injury, hence it is a sign that the centers to encode new memories may not be functioning. Retrograde amnesia is difficulty remembering things that occurred before the injury, and is more of a sign of difficulty in retrieving old memories.
Amnesia. Antigrade amnesia is an inability to lay down new memory traces, from the time of a brain insult forward. Retrograde amnesia is the loss of memory from the time of brain insult backwards in time.