Amnesia can be experienced as anything from a temporary absence of memory to an enduring loss causing severe disruption in a person’s life. However, even in prolonged amnesia, the brain is sometimes able to find new ways of remembering information.
Amnesia is defined as the temporary or permanent impairment of some part of the memory system. For instance, children who witness a horrific crime – like the murder of a parent – may blank out the experience totally at the time. But skilled questioning by experienced police officers and psychologists, often using models, can often draw out at least some of the story over time. In such cases, amnesia is only a temporary state. Even in its most enduring forms, amnesia is rarely a total wipe-out of memory. For example, people who care for patients with Alzheimer’s disease, which is characterized by a gradual decline in memory and other mental skills, are frequently surprised by the level of memory that remains. Sufferers might forget they had break fast or how to find their bedroom, yet may be able to name everyone in a family photograph from long ago.
Causes of amnesia
Amnesia is generally caused by some form of brain damage, which may be the result of head injury, stroke, infection, or disease. More rarely, psychological trauma leads to a type of memory loss known as fugue, in which people temporarily lose their true identity. Crime writer Agatha Christie suffered from vogue, said to be caused by the stress of a marriage break down, and disappeared under a false name for several weeks. Like most sufferers, she made a full recovery.
Among younger people, trauma, such as a motor cycle accident, is the major cause of brain damage that leads to amnesia. A sharp jolt to the brain can cause twisting of the meninges – the delicate membrane that protects the brain – and damage the temporal lobes, one of the major areas involved in memory. Afterward, the victim may suffer a state of disorientation known as post-traumatic amnesia. In a typical scenario, it may take several days before someone who has been knocked down by a car can recognize their partner. Post-traumatic amnesia may last for hours, days, or even months, but a complete recovery is usual. Alzheimer’s disease and stroke are the main causes of more permanent forms of memory loss in older people. These forms include retrograde amnesia, involving the loss of memories from before the illness, and anterograde amnesia, which affects memory performance after the damage.
Retrograde amnesia
In one famous case of retrograde amnesia, related by Oxford neurologist Ritchie Russell, a 22- 22-year-old man was thrown from his motorcycle. When he recovered consciousness, he insisted that the date was eleven years earlier and that he was still a schoolboy. It was as if the eleven years up to the accident had never happened. As is often the case in retrograde amnesia, as he recovered, the gap between his most recent memory and the traumatic event began to shrink, and memories began to return, albeit patchily. Two weeks after the injury, he recalled spending five years in Australia during this lost period. However, a week later, he returned to a village where he had lived for two years and had no recollection of it. Ten weeks after the accident, the memory gap had closed completely, except for the few minutes before the accident.
As with most cases of trauma, the memory of the accident that caused it was extinguished forever. Research on American foot ballers who have been knocked out during a game suggests that the injury itself interferes with the brain’s ability to lay down a memory of the event.
Anterograde amnesia
Anterograde amnesia is the most striking form of memory loss, sometimes occurring alone or with retrograde amnesia. When amnesia affects the ability to store new information in memory, this usually has a catastrophic effect on a person’s ability to keep track of daily life. In Alzheimer’s disease, such memory problems usually develop gradually. For example, one sufferer managed to hide the increasing chaos of her days until she lost her way back to the table during a family meal in a restaurant.
A similar inability to lay down memories occurs in Korsakoff’s syndrome, a condition caused by widespread damage to the brain as a result of long-term alcoholism. Typically, Korsakoff ‘s patients fill in the gaps in their memories by confabulation – concocting false details. If the reality-checking frontal lobes of the brain are also affected, they may be unable to distinguish between real and fabricated events.
More rarely, anterograde amnesia results from localized damage to the hippocampus. A person much-studied · by psychologists, known by his initials HM, had a large chunk of his hippocampus removed surgically in the 1950s as a treatment for epilepsy. Afterward, he could not remember anything from the previous two years and has never regained the ability to lay down memories. He is now an older man but still believes he is in his late twenties. When given a mirror, he is briefly puzzled by the face that stares back – but within a few minutes, he has forgotten it.
Recovering memory
Although memory loss can be permanent or continue to worsen, in some cases, the brain is able to create new routes to memories. The brain operates as a network of neurons extending over large areas, so if a circuit is disrupted by damage, for example, by a stroke, memories can sometimes be retrieved using different pathways. Learning new ways to approach tasks can help this process, and outside cues and prompts can also be useful. A timer buzzer that minds a person to do something at a particular time can be a great help.
Recovery is possible in some cases, even when the initial effects are severe. Clinical psychologist Malcolm Meltzer suffered brain damage because of temporary oxygen deprivation when he had a heart attack at age 44. At first, there were gaps in his autobiography and, unusually, some loss of skills – he had to relearn how to operate the stereo and use a razor. His working memory was particularly affected, making planning and organization of ordinary tasks such as paying bills or going on holiday impossible. He could not remember the plot of a book or a film for long enough to see it through to the end. However, Meltzer’s condition improved steadily, and eventually, he was able to write an article about his amnesia that offered valuable insights into the condition.
Learning From Amnesia
The way some types of memory are selectively impaired as a result of brain damage has taught researchers a lot about how memory might be organized in the brain. In particular, our procedural or ‘how-to’ memory for skills, such as reading or making a pot of tea, seems to be relatively resistant to damage. Severe amnesics who are unable to lay down any new memories of facts or events can often still have remarkably effective procedural memory. Clive Wearing was still able to play the piano despite severe amnesia caused by encephalitis. In addition, amnesics can often, to their surprise, learn new skills. Procedural memory involves different brain areas from those needed for conscious, factual memories. Storage and retrieval of procedural memories involve the cerebellum and the putamen – two quite separate brain areas that can remain intact and retain their function even when large areas of the outer parts of the brain are damaged.
Visualizing memory loss
In his painting, The Disintegration of the Persistence of Memory, Dalf shows a landscape from an earlier work shattered by an atomic bomb. The painting is often used to represent the devastating effects of Alzheimer’s disease.
Testing For Amnesia
The Rivermead Behavioural Memory test is designed to identify which aspects of amnesia are present that might cause problems in everyday life.
Among other tasks, participants are asked to :
- Give the date
- Remember the name of an unfamiliar face
- Remember an appointment
- Recognize a picture shown previously
- Recall a newspaper story – immediately and later
- Remember a new route
- Remember to deliver a message
Critical Areas For Memory
Amnesia is generally the result of damage in areas that are important in memory – crucially, the temporal lobes, situated near the temples, and the hippocampus, which has a major role in the laying down and retrieval of memory.
The frontal lobes – behind the forehead – are also important. They are large in humans compared to other animals and are thought to be linked with ‘higher’ mental functions. People with damaged frontal lobes appear normal in many ways, but they are unable to plan and organize their actions and may have problems with short-term memory. Damage to the frontal lobes also seems to affect a person’s ability to distinguish familiar items from similar unfamiliar ones. This may be why many sufferers find it hard to separate memories of real events from imagined ones.
Healthy brain
In this scan of the brain of an older man with no evidence of amnesia, the arrow points to the hippocampus, showing its normal size.
Brain in Alzheimer’s
Loss of brain tissue in a patient with Alzheimer’s disease is revealed by the increased size of the dark cavities (ventricles ) and a shrunken hippocampus.
