Amnesia means a temporary or permanent loss of memory. Amnesia can be caused by brain trauma or physical damage to the brain from wounds, tumors, viruses, or lesions; degenerative brain diseases such as Alzheimer’s disease; seizures; certain drugs or alcohol; and by mental disorders such as post-traumatic stress. Amnesia that is the result of psychological factors is called psychogenic amnesia. Most episodes of amnesia last a few seconds to a few hours, but in rare cases, amnesia can last for months or even years. The worst case of amnesia ever recorded was that of British musician Clive Wearing, whose brain was damaged from a bout of encephalitis virus in 1985. Since that time, he cannot form memories that last longer than seven to 30 seconds.
Amnesia can take away different forms of memories. The ability to remember things that just happened a few minutes ago or “short term memory” is most often affected. People with this kind of amnesia can retain “long-term memories” of their childhoods and adolescence and yet be unable to remember things that happened a few minutes ago. “Procedural” memories involve habits and abilities, such as playing the piano or riding a bicycle. Amnesiacs can usually retain procedural memories more than “declarative memory,” which is the ability to remember facts.
Infantile amnesia refers to the fact that no one can remember what happened during their first few years of life.
Transient global amnesia means a sudden, temporary memory loss whose cause is sometimes unknown, in that it cannot be attributed to a common condition such as epilepsy or stroke. Transient global amnesia is a rare condition that usually goes away on its own and does not last very long. Two risk factors for transient global amnesia are migraine headaches and being over 50 years old.
Anterograde amnesia is the loss of the ability to create new memories along with an inability to recall the very recent past. Benzodiazepines and alcohol can cause anterograde amnesia. This form of amnesia is probably the result of a failure to properly store memories because victims are able to process and encode new information normally.
Retrograde amnesia is the inability to recall any events before the amnesia developed. Victims can usually recall events from the long-ago past but events nearest to the event that caused the amnesia are usually lost forever.
Psychogenic amnesia is sometimes called dissociative amnesia in that the person can lose his identity and enter a “fugue state” lasting for a few hours or days, most often after experiencing severe stress or trauma. Post-traumatic stress disorder can disturb the normal workings of memory, in that the person experiences sudden and uncontrollable “flashbacks” or intrusive thoughts about a traumatic event. Post-traumatic amnesia occurs after traumatic brain injuries and causes the person to be disoriented and unable to remember who they are, where they are, etc. The famous psychologist Sigmund Freud believed that psychogenic amnesia is a defense mechanism against suicide or severe anxiety.
When you visit a physician because of amnesia, you will usually undergo various tests, such as magnetic resonance imaging and an electroencephalogram, in order to determine the organic basis of the problem. If you have a brain tumor or other organic disease, your doctor will treat that condition. There is no known drug or cure for amnesia, although many patients improve through memory training and using high-tech devices such as Blackberries or low-tech ones like calendars to help them remember appointments and so forth.
Alcohol is a drug that impairs short-term memory and the encoding of memories, which is why many people cannot remember events that occurred while they were intoxicated. If a person drinks too much for many years, he may develop a deficiency of thiamine. This will lead to Korsakoff’s syndrome or Wernicke-Korsakoff syndrome, in which the person loses the ability to form new memories but can recall the past. Patients with this syndrome often make up stories as substitutes for the memories they have lost.
Age-associated memory loss is not amnesia, but rather the natural degradation of memory function that occurs as people grow older.