Learning, Memory, and Amnesia

Types of Amnesia

Memory lapses are common. We all have them from time to time; everyone forgets and sometimes it can be rather embarrassing. Most people don't have great memory. Unfortunately, some people have much more severe conditions in memory problems. These memory deficits can occur when people have brain injury, Alzheimer's disease, or stroke. In the classic amnesiac syndrome, there is a deficit in episodic memory, but long-term memory and cognition is unimpaired.

Anterograde amnesia is when people are no longer able to form new memories. It is a problem of encoding, storing, and retrieving future memories. Retrograde amnesia is when you can no longer access past memories. You have difficulty accessing events that happened in the past, typically before the disease or injury that caused the retrograde amnesia.

Post-traumatic amnesia (PTA) occurs after a severe concussive head injury and you have difficulty forming new memories. This condition typically improves over time. Traumatic brain injury (TBI) occurs when the head receives receives a sharp blow or jolt. This can occur from a fall, a car crash or collision, etc.When a post-traumatic amnesiac recovers consciousness from the injury, their attention and capacity for new learning can be grossly impaired or disturbed. Post-traumatic amnesiacs who suffered severe brain injury typically recovered personal knowledge first -- who they were, their identity. They then recovered place -- where they were. Finally, they recovered temporal orientation -- the time and date, when they were. The recovery is gradual and the recovery time varies. After recovery, retrograde amnesia can persist, but it can shrink with time and rehabilitation.

Transient global amnesia (TGA) occurs when someone suddenly develops severe difficulties in forming and retrieving new memories. This can happen to relatively normal individuals with no previous problems in memory. Fortunately, this condition tends to resolve on its own and can resolve rapidly as well. However, the specific cause for this condition is still unknown.

Suffering from amnesia is a frightening thought. I believe we take our memory for granted because some people aren't as lucky as us -- some people can't even remember what happened 30 seconds ago. Whenever I forget something or have a poor memory, I usually get mad at myself for forgetting but now I'm glad that I have the ability to forget some small, trivial things sometimes -- some people can forget who they are, where they are, and when they are.

Even though amnesiacs have problems with new episodic learning, they can learn through classical conditioning. They can also learn through priming and have relatively intact implicit and procedural learning. A famous case of amnesia is Clive Wearing who suffers from varying degrees of anterograde and retrograde amnesia, however he still has his implicit memory intact. Below is a brief YouTube clip of Clive Wearing displaying his amnesia, but at the beginning you can see him playing the piano which clearly shows intact implicit memory: