Amnesia

What is amnesia?

Amnesia means loss of memory. The temporary inability to put a name to a familiar face is something we all experience. Once we remember the name it is hard to understand how we forgot it.

Strictly speaking amnesia really means loss of certain memories, rather than a general loss of the ability to remember anything — something that is much rarer. The process of memory is complex and not fully understood. It seems that different areas of the brain are involved in different types of memory — which is really an information storage system rather like a filing cabinet or computer.

Causes of amnesia

Many things can cause episodes of amnesia. These include infections and injuries to the brain, drugs, seizures, stroke and reduced blood circulation, particularly in older people.

In dementia, most often seen as Alzheimer’s disease, recent memories are lost first, while the memory of things in the distant past often remains crystal clear.

Transient global amnesia

An alarming but non-serious form of temporary amnesia is known as transient global amnesia (TGA). TGA is a sudden temporary episode of memory loss. Affected people are usually middle-aged or elderly. They appear quite normal, know who they are, recognise people they know well and can function quite normally in activities such as driving a car. However, they have a profound loss of recent memory, and are unable to form new memories during the episode. An episode may last for a period of 4 to 8 hours, but sometimes up to 24 hours. Understandably this is a very frightening experience, both for the affected person and those around them.

Transient global amnesia symptoms

People with transient global amnesia will usually keep repeating questions and appear anxious, agitated and perplexed. And they will be fully aware that there is an inexplicable blank period in their memory.

Causes

We do not know why transient global amnesia happens. Migraine variants and mini-strokes have all been suspected as causes. TGA can be precipitated by extreme physical activity, sudden immersion in cold or hot water, accidents or strong emotional experiences. Having had an episode of transient global amnesia does not mean that a stroke becomes more likely, or that the person is suffering from any other physical problem.

TGA needs to be distinguished from other things which may cause memory loss, some of which may be life-threatening, such as seizures, stroke, fainting episodes and the effect of drugs.

Recovery

Recovery is usually very rapid and complete. The risk of having a second attack within 5 years is reported as anything between 3 and 20 per cent.

What to do if you or someone else has sudden memory loss

Because there’s no easy way to tell transient global amnesia from potentially life-threatening conditions that can cause sudden memory loss, seek immediate medical attention if you or someone you know has sudden memory loss and goes from being aware to being confused about what just happened.

Last Reviewed: 13 February 2013
Your Doctor. Dr Michael Jones, Medical Editor.

References

1. Mayo Clinic. Amnesia. Updated Oct 11 2011. http://www.mayoclinic.com/health/amnesia/DS01041 (Accessed Feb 2013).
2. Mayo Clinic. Transient global amnesia. Updated Aug 18 2011. http://www.mayoclinic.com/health/transient-global-amnesia/DS01022 (accessed Feb 2013).
3. Owen D, Paranandi B, Sivakumar R, Seevaratnam M. 2007. Classical diseases revisited: transient global amnesia. Postgrad Med J 2007: 83: 236-239. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2600033/pdf/236.pdf (accessed Feb 2013).

Dr Michael Jones

Dr Michael Jones

Medical Editor, Your Doctor.