Amnesia

What is amnesia?

Amnesia is loss of memory. It is not the same as simple forgetfulness. If you have amnesia, you cannot remember anything that happened during a specific time period. However, you do not forget everything about the past.

The 2 main types of amnesia are:

• Retrograde amnesia. This is a loss of memory before an event. For example, you forget what happened right before a blow to the head.
• Anterograde amnesia. This is a loss of memory that occurs after an event. For example, you forget what happened right after having surgery. Many people in severe car accidents have amnesia that affects the time just before the accident and also for a time afterwards.

What is the cause?

Amnesia may be caused by:

• a blow to the head
• a brain tumor
• dementia
• a horrifying event, such as a rape or seeing a murder or suicide
• poor diet or vitamin deficiency
• medicines such as sleeping pills and anesthesia used in surgery
• mental disorders such as dissociative identity disorder
• poisons such as carbon monoxide
• stroke
• alcohol or substance abuse.

Another type of amnesia is called transient global amnesia (TGA). TGA is caused by decreased blood flow in the brain. The amnesia can last anywhere from 1 to 24 hours. You may have a headache, dizziness, and nausea, or you may have only memory loss. It may happen only once or many times.

What are the symptoms?

Besides not being able to remember certain events, amnesia can make it hard to learn. You may be disoriented and confused.

How is it diagnosed?

A healthcare provider or a mental health specialist will ask about your symptoms and any drug or alcohol use. The following tests also may be done:

• blood tests
• brain wave tracing (EEG, or electroencephalogram)
• CT scan
• MRI
• tests to evaluate how well you can concentrate, remember, understand, and make decisions.

How is it treated?

Treatment depends on the cause. Psychotherapy can be helpful if your amnesia is caused by emotional trauma. Hypnosis may help some people. Sometimes medicines such as nimodipine (Nimotop) are prescribed for victims of head injuries to relax blood vessels and improve blood flow to the brain.

In most cases, amnesia is short-term and only lasts a few seconds to a few hours. However, it may last a few weeks or even months if the trauma or injury was severe. As the person recovers, older memories usually come back first, and then more recent memories. Almost all memory is recovered, except what happened around the time of the accident.