Amnesia is a deficit in memory caused by brain damage or disease. Amnesia can also be caused temporarily by the use of various sedatives and hypnotic drugs. The memory can be either wholly or partially lost due to the extent of damage that was caused.
Amnesia occurs in fiction a lot more often and readily than in real life. That has not stopped it becoming a popular theme or plot device for writers as it presents a ready-made mystery. If you want to take a deep dive, TV Tropes has a huge section on memory.
There are two main types of amnesia:
- retrograde amnesia
- anterograde amnesia
Retrograde amnesia is the inability to retrieve information that was acquired before a particular date, usually the date of an accident or operation. In some cases, the memory loss can extend back decades, while in others the person may lose only a few months of memory.
Anterograde amnesia is the inability to transfer new information from the short-term store into the long-term store. People with this type of amnesia cannot remember things for long periods of time.
These two types are not mutually exclusive; both can occur simultaneously. Read a factual description if you are keen on realistic use in fiction.
