If someone has anterograde amnesia, he or she can't remember incidents that happen after the onset of amnesia. A less common device in television or movie scripts, this form of amnesia is central to the plot of the movie "Memento." The main character receives a severe blow to the head and suffers brain damage. Similar to other victims of anterograde amnesia, he can no longer form new memories.
As an amnesiac recovers, he or she usually recalls older memories first, and then more recent memories, until almost all memory is recovered. Memories of events that occurred around the time of the head trauma or onset of amnesia are sometimes never recovered.
When people talk about memory, they're usually thinking about long-term memory. People actually have several different types of memory. The three most important types to consider when thinking about amnesia are:
- Short-term memory refers to memories that last anywhere from a few seconds to a couple of minutes.
- Intermediate long-term memory refers to memories that may last for days or even weeks, but eventually are lost forever unless they are moved to long-term memory.
- Long-term memory refers to memories that can be recalled for many years or perhaps for an entire lifetime.
In order to understand how the loss of memory works, knowing how we store memories in the first place is helpful. The human brain is a truly amazing organ. It gives us the power to think, plan, speak and imagine. It also gives us the ability to make and store memories. Physiologically speaking, a memory is the result of chemical or even structural changes in synaptic transmissions between neurons. As these changes occur, a pathway is created. This pathway is called a memory trace. Signals can travel along these memory traces through the brain.