Amnesia

Amnesia (am-NEE-zha) is loss of memory.

What would it be like to wake up one morning and not know who you are, not recognize your home or your parents, or not be able to account for your actions in the past days? This image of amnesia has been the basis of many movies and books. Amnesia is a gap in a person's memory. Although a short period of amnesia is fairly common, especially after a head injury, true amnesia is rarely as dramatic and extensive as it is portrayed by writers and filmmakers.

Types of Amnesia

There are three distinct phases to memory: registering the event in the brain, storing the information, and retrieving the information that has been stored. Problems in any of these phases may cause amnesia. The source of the problem can be either physical or psychological. The memory gap can be of events either before or after the trauma or other problem triggering the amnesia, and it may be temporary or permanent. There are several distinct types of amnesia:

• Anterograde amnesia is the inability to learn new information. A person with this type of amnesia can accurately recall events in the past, before the trauma, but has marked difficulty remembering any new information for more than a few minutes.
• Retrograde amnesia is the partial or complete loss of memory of events that occurred before the trauma. New information, however, can be processed, stored, and recalled correctly.
• Transient global amnesia is a form of memory loss that appears suddenly and causes confusion, disorientation, and forgetfulness for 30 minutes to 24 hours. This type of memory loss normally clears up on its own, but a person experiencing transient global amnesia also may experience temporary retrograde amnesia.

What Causes Amnesia?

Most often, amnesia has a physical cause. The leading cause of amnesia is an injury to the head. For example, a hockey player who falls and hits his head hard on the ice may be unable to recall the events, or their sequence, immediately before he fell. A head injury that leads to temporary loss of consciousness or amnesia is called a concussion (kun-KUH-shun). Retrograde amnesia, either permanent or temporary, is very common in people who are in car accidents. People who have head injuries in a car accident rarely, if ever, remember the accident. While the body may heal, the retrograde amnesia usually is permanent.

There are other physical causes of amnesia, for example, when there is not enough blood flow to the brain (which is thought to be the usual cause of transient global amnesia), or when there is brain cell damage from long-term alcohol abuse. This condition, called Wernicke-Korsakoff (VER-ni-kee-KOR-sa-kof) syndrome, often produces anterograde amnesia. Malnutrition and brain infections are other physical conditions that may produce amnesia. People with Alzheimer disease frequently have amnesia, which is thought to be caused by physical changes in the brain. Treatment for amnesia involves treating the condition causing it, if possible.

When amnesia has psychological causes, it is called psychogenic (sy-ko-JEN-ik) amnesia. This type of amnesia is not common. It may occur when a person suffers a physically or emotionally overwhelming event or trauma (for example, witnessing the murder of a loved one). The memories of the traumatic event and the circumstances surrounding it are so upsetting that they are repressed. The repression is not done consciously, and it may be temporary or permanent. Treatment involves psychotherapy ^* . The use of hypnosis to recover lost memories is controversial since in some cases the "recovered" memory may not be real, but the result of suggestion by the hypnotist.