People who get amnesia are unable to retrieve memory stored in their brains. Their brain has somehow become compromised, usually through injury or a traumatic experience.
Ordinarily amnesiacs can function as normally as they did before, in all areas such as language and speech, processing information and even doing complex math. The exception is that they simply can’t access the portion of their brain that pulls up memory. The limbic system, which does not actually store memory (several areas of the brain do that, depending on the type of information to be stored), is involved in the retrieval of it. The limbic system consists of the hippocampus, the amygdala, and parts of the cortex. Besides memory, the limbic system is responsible for the coordination of motivation and emotions, and for some of the functions of the endocrine system.
From the two types of memory: short-term memory or working memory, which stores information needed for a very short period of time; and long-term memory, which is used in the relationships among objects and procedural memory. Amnesia can affect both relational memory and short-term memory. Memories that represent single functions – like riding a bicycle, remain intact. This could explain why amnesiacs can often remember basic skills and motor functions, while losing memories.
The most common form of lost memory is called “anterograde amnesia.†It involves the ability to store, retain or remember new information after the triggering event occurs. A good example could come from the Adam Sandler, Drew Barrymore movie 50 First Dates, where Drew’s character could only remember things that happened up until the time of her accident. Every day she would wake up and just not remember what happened the day before. They make up stories to fill in the events they can’t remember. Their short-term memory works, and they can carry on a conversation, but if they become distracted the memory of the conversation may fade away. This is what happens with dementia and Alzheimer’s patients (anterograde amnesia).
The funny thing about amnesia is that, although some memories may be hard to retrieve, the person can have excellent memory function in other areas. That could mean that an individual with amnesia may have good childhood memories, and remember the years before their injury, but remember little or nothing from then on.
Amnesia can be caused by a variety of things, the most common are: stroke; Alzheimer’s disease; traumatic brain injury or head trauma; seizures; brain infection, such as encephalitis or meningitis. Less common causes include: brain tumor; psychiatric disorders like schizophrenia; depression; psychogenic amnesia, which usually occurs after a serious threat to life or health; or criminal behavior – studies have shown that 23%-65% of murderers claim amnesia for their crime.
What does actually cause the memory loss? No one is actually certain. A study using rats suggested that memory loss is probably due to an error in memory retrieval. It could also be a by-product of swelling in the brain caused by the injury. This could explain why some amnesiacs are actually able to recover their memories after some time – perhaps when the swelling subsides.
It can’t be easy, for an amnesiac or their loved ones, to not be able to remember things that happened to you before or after a trauma. Memory is a complex part of the brain, and requires a lot of different areas. Fortunately, many of them work independently of each other so not all other functions are affected.
From the Desk of Ron White
Sources:
Wikipedia – Anterograde amnesia: http://en.wikipedia.org/wiki/Anterograde_amnesia
Memory Loss and the Brain – Anterograde Amnesia: http://www.memorylossonline.com/glossary/anterogradeamnesia.html
Life Extension – Amnesia and Memory Loss: http://www.lef.org/protocols/neurological/amnesia_01.htm