What Is Amnesia?

On January 12, 2005, a young man in his late teens was found in a dirty snowbank in the town of Weymouth, Massachusetts. He had suffered a head injury. He was treated at a hospital and was then sent to a homeless shelter. The man had no memory of his name, where he was from, how he had ended up in the snowbank, or anything else that had happened to him before he was discovered lying dazed in the snow. He was taken in by a woman who gave him a place to stay until he could remember who he was or until his family could find him—if he had a family at all.

“I just want to have my memory back,” he said. “I hope someone is looking for me.”¹²

This is one of very few true stories of amnesia that reads like a book or a movie script, but it is easy to see why there are so many movies about amnesia. What could be more interesting than a person who wanders into town with no idea who he is or how he got there? The reality is that people with amnesia are just regular people with an unusual problem. They have lost a chunk of memory, and with it, part or all of their identity.

The human brain is very complicated. The process of how it makes and stores memories is not well understood, and therefore, the way memories are lost is also not well understood. People suffering from amnesia are victims of a very perplexing problem that may have no solution.

Memory Loss Comes in Many Forms

Amnesia is a very general word describing any loss of memory. There are, however, different types of memory, so there are also different types of amnesia. The amnesia that affected HM so that he could not learn or remember anything new was very different from the amnesia that affected the young man in the snowbank, who could learn and remember everything after his accident but nothing before. Understanding which part of the brain has been damaged, whether by accident or illness, sometimes helps doctors figure out what type of memory a patient with amnesia has lost. Sometimes, patients and their doctors must simply wait to see which memories return and which do not.

One of the most puzzling things about any kind of amnesia is that it usually only affects certain kinds of memory. Some patients lose long-term memories. Some lose the ability to form short-term memories and learn new things. Some people lose explicit knowledge—the facts and the memories of specific experiences that make up their personal history. But for some reason, implicit memories, the skills and habits a person does without thinking, are rarely lost.

Scientists use these facts as proof that the memory process involves most or all of the brain. Damage to one part of the brain may wipe out one type of memory but not others. Amnesia leaves most people nearly whole and mostly normal—except for a chunk of missing memories.

The Long and Short of Memory

Just as the brain is a master at remembering, it is also very good at forgetting, even when a person does not have amnesia. A huge amount of information goes into the brain every day. Most of this—the color of a pebble in the driveway, the number of swallows it took to finish a glass of orange juice in the morning—is information a person will never need. The brain is very good at sorting out the important things and dumping all the rest to make room for memories that will be made tomorrow.

“Much learning in daily life can be labeled ‘updating,’” says Robert W. Howard in his book, Learning and Memory: Major Ideas, Principles, Issues and Applications. With time, he explains, a person’s knowledge about various things must change to stay current. “Destructive updating,” he says, “is getting rid of no longer current information.”¹³

When the brain decides a detail is worth keeping, at least for a while, it sorts the information into a memory for the short-term or for the long-term. Short-term memories are things the brain will probably use again soon. These are the details that help someone plan a day or a week, for example. If a teacher says there will be a spelling test tomorrow, students will need to store that information, at least until tomorrow. They probably will not need to remember the conversation in ten years, so this may become a short-term memory, one that is forgotten when it is no longer needed. Short-term memory is hard at work during a movie, too, forming memories of what happened at the beginning so that everything makes sense at the end. The brain quickly forgets the name of the movie’s producer, which appeared in the credits at the start of the film, but when the movie is over, the brain forms a long-term memory of watching it. This memory will probably exist for life.

“It seems unlikely that long-term memories fade as a simple by-product of time,” says author James S. Nairne. “New memories compete and interfere with recovery of the old,” he explains, but with the right kind of cues, “previously forgotten material becomes refreshed and available for use once again.”¹⁴

Over time, as a person gets older and learns new things, the brain stores a lot of information in its long-term memory. Some of the memories are facts and some are skills. Together, these

Erase This, Please

It is hard to imagine anyone wanting to lose his or her memory. People who have lived through something very terrible, however, sometimes wish they could wipe out their memories of that one event. In April 2007 French and American scientists reported finding a medication that might be able to do just that. Rats that were trained to be afraid of a certain sound were given the drug, and afterward, the same sound no longer frightened them. The scientists believe that when a bad memory is pulled out of long-term storage in the brain, the drug might be able to prevent it from being stored again. Thus, the bad memory could be forgotten, while no other memories would be destroyed. If this medication were to work the same way in humans, there might one day be a cure for the terrible mental effects of war, natural disasters, accidents, and other terrifying events.

make up the two types of long-term memory, one of which happens to be much more vulnerable to amnesia than the other.

Implicit and Explicit Memory

The brain is able to form two main kinds of long-term knowledge. One of the brain’s main tasks is remembering how to do things. The brain’s other job is keeping track of what is known. Scientists often describe these two types of memory as the difference between “knowing how” and “knowing that.”

Knowing how is called implicit memory, or procedural memory. It is the memory of a procedure, or how to do a certain thing. Riding a bicycle is one example. It can take a lot of practice and a lot of skinned knees to learn how to ride a bike, but once the brain has learned, it does not forget. The phrase it’s just like riding a bike is based on science—once the brain knows how to do something, it stores this knowledge for life. A person who has not climbed onto a bike for years will be able to place his feet on the pedals, and without thinking about it, ride around the block. The brain has stored this memory, and it is implicit: A person does not have to think about how to ride a bike.

People have many implicit memories, usually for the things they spend a lot of time practicing. Riding a skateboard, reading a book, or playing the piano are examples of implicit memories. Once a person masters these skills, she can do them without thinking about them. She does not need to learn them again every time.

“Information in implicit memory is unconsciously held, resists forgetting, shows little transfer beyond training stimuli, and is acquired through practice,”¹⁵ says Howard.

The other type of long-term memory is called explicit memory, or declarative memory. Explicit memories are things we can declare or talk about. These are the facts we learn over time. If implicit memory is knowing how, explicit memory is knowing what. This is the kind of memory created when some- one studies for a test. Instead of practicing a skill, he is memorizing facts.

Explicit memories are usually things people have to think about. Recalling presents from a birthday years ago might take a while. The brain stores many facts for the long-term, but that gets to be an awful lot of information over time. Brains have to work harder to find information from long ago.

“Information in the explicit system is consciously available,” says Howard, but “is prone to forgetting.”¹⁶

The brain seems to store different types of knowledge and facts in different places and in different ways. Amnesia usually causes the loss only of certain memories or certain types of memory. This leads to different types of amnesia. The two forms of amnesia that are perhaps most troubling for their victims, and the most difficult for doctors to understand, usually come from some kind of head injury, and they involve the loss of memories made either before or after that event.

Anteretrograde Amnesia: The Loss of Memory-Making Abilities

At age twenty-seven, the young man known as HM lost his ability to remember anything new. From the day of his brain surgery forward, he could not form new memories. He has continued living for many years after the surgery, but as far as his brain is concerned, his memorable life lasted twenty-seven years, and not a day more.

The loss of the ability to remember any new facts or events after amnesia sets in is called anteretrograde amnesia. It is usually caused by damage to the brain, whether from an injury or a medical condition. A person with anteretrograde amnesia, such as HM, cannot remember any new information. Memories of recent experiences quickly disappear, although the person can clearly remember things that happened before the brain injury.

“The key to understanding patients like H. M. is realizing that their disorders are highly selective,” says Harvard Univer-sity psychology professor Daniel L. Schacter. “Various kinds of knowledge and skills are all spared.”¹⁷

For patients like HM, who have anteretrograde amnesia, the condition may be more difficult for their loved ones than for them. After all, these patients may forget that they cannot remember.

“There is a kind of poetic justice at work for patients with [anteretrograde] amnesia,” says Schacter. “The impairment might mercifully serve a protective function by preventing patients from becoming aware of the catastrophic nature of their memory loss.”¹⁸ Sadly, this is not the case for all people with amnesia.

Retrograde Amnesia: The Loss of Memories Themselves

The man who was found in a Massachusetts snowbank could be described as the opposite of HM, in terms of memory loss. This man, who could recall nothing before waking up in a snowbank, is a victim of retrograde amnesia. This form of amnesia wipes out long-term memories stored in the brain, or at least, it blocks the brain’s ability to find them.

Unlike HM, the man in the snowbank was perfectly able to learn new things and form new memories. He made a friend at the homeless shelter and remembered not only her name but her phone number. He was able to recall everything that happened to him after he was found in the snow. But he knew absolutely nothing of his past. He did not remember his name or his birthday, his family members or his hometown. He did not know if he had brothers or sisters or if his parents were still alive. He could not name a single hobby he had before or a sport he could play (although quite possibly, if he had been a guitar player before, he might well have remembered the implicit skills of what to do with the instrument if one was placed in his hands).

One of the most interesting things about retrograde amnesia is that only certain kinds of long-term memories disappear. The person with this kind of amnesia has not lost everything he or she ever learned before. The man in the snowbank could still talk, for example. The years of new words he had been learning since birth were still in his memory. He did not wake up in the snow with the mental abilities of an infant. Indeed, he walked, talked, and acted every bit like the grown man he was. He simply had no memory of the process of growing up, or of the accident that robbed him of his memories.

Living with retrograde amnesia must be very difficult. Imagine the frustration of waking up each day knowing that your past has vanished, and try as you might, you simply cannot get it back. In her book, Past Forgetting: My Memory Lost and Found, amnesia sufferer Jill Robinson describes what it is like to live with amnesia: “I walk through the dark driveway to my house. I open the door. The house is dark and still and empty. I walk through each room and not only is nothing here, I don’t even remember what was here.”¹⁹ Amnesia made her feel like a stranger in her own life.

Transient Global Amnesia

Because they are usually caused by damage to the brain, retrograde and anteretrograde amnesias are especially frightening—these memory problems can be permanent. Movies and soap operas featuring people with amnesia are often misleading, because characters may get back all of their memories or their ability to make new ones. When the brain has been damaged, this does not always happen.

There are times, however, when the brain does recover from amnesia, and memories can be restored. One type of amnesia, called transient global amnesia, has no known cause at all. It is a sudden, severe, but temporary loss of memory. According to the staff of the Mayo Clinic, during an episode of transient global amnesia, “your recall of events simply vanishes, so you can’t remember where you are or how you got there . . . you do remember who you are, and you recognize family members and others you have known for a long time, but that knowledge doesn’t make your memory loss any less disturbing.”²⁰

Transient global amnesia strikes with no warning. Although this kind of amnesia sometimes follows a shocking event such as getting bad news or jumping into a very cold swimming pool, there is no definite cause. Fortunately, these episodes are very rare, and when they do happen, they do not last long. A person who has experienced this type of amnesia once will probably never have it again.

“Episodes of transient global amnesia last only six hours, on average,” say experts at the Mayo Clinic. When an episode is over, “you remember nothing that happened while your memory was impaired, and you might not recall the hours beforehand. Otherwise, though, your memory is fine.”²¹

Transient global amnesia gives its victims a glimpse into the life of someone who lives with permanent memory problems. Because the condition is temporary, sufferers of transient global amnesia do get their memories back. But every case of amnesia serves as a reminder that memory is a very fragile and mysterious thing. Even when a brain injury has never happened, memories might be lost simply because the brain has

False Confessions

Memories are not always that reliable. (Anyone who has aced a test in school and forgotten all the information by the next day can confirm this.) The idea of amnesia sometimes leads to false confessions—when people admit to crimes they did not commit.

In a police interrogation room, a nervous suspect who had nothing to do with a crime might begin to doubt his own memories. The interrogator asking the questions might suggest that the suspect “forgot” committing the crime, and the suspect might begin to fear that he really did have amnesia for a short while. He might even confess to the crime, although his statements will usually be as foggy as his false memories: “I guess I must have done it, then.”

Fortunately, such false confessions do not always hold up when questioned in court.

reached some sort of overload. The brain can force forgetfulness on itself when the pain of a certain experience or memory is simply too overwhelming.

Psychogenic Amnesia

After natural disasters or other ordeals that cause trauma to a great many people, psychiatrists often see a rise in the number of patients seeking treatment for mental or emotional problems. Some of these patients are troubled by memories of the terrible event they have experienced. Other patients may be having the opposite problem—they cannot remember anything about the horrifying experience at all.

The sudden loss of memory that is linked to an extremely disturbing, often life-threatening experience is called psychogenic amnesia. Scientists have been studying cases of this kind of forgetting since the 1870s. By the end of the nineteenth century, “psychiatry had become alerted to the pathogenic influence of persistent memories (both conscious and unconscious) of traumatic events,” say Martin T. Orne and his colleagues in their article, “Reconstructing Memory Through Hypnosis.”²²

Psychogenic amnesia tends to happen to people who have no history of mental illness but who have lived through something terrifying, such as an earthquake, getting mugged, or a violent battle during a war. Most people who have psychogenic amnesia realize that they have lost some of their memory. Usually, the missing memories are of the traumatic event itself and/ or a short period of time right after it. Brain injury is not the cause of this kind of amnesia. (If a brain injury did occur, the amnesia would be classified differently.) Many doctors and scientists who study cases of psychogenic amnesia believe that it is caused by the brain itself as protection against memories so painful or troubling that the person would not be able to cope with them.

“Indeed,” says Dr. Theodore G. Brna Jr., “psychogenic amnesia often improves spontaneously with apparent resolution of the underlying conflict.”²³

Like most other forms of memory loss, psychogenic amnesia is not well understood. However, this type of amnesia, in particular, is interesting to many people dealing with difficult situations or emotional troubles they cannot seem to explain. Studies show that half of all murderers claim to have had some kind of psychiatric amnesia when they committed their crime, and there has been a recent increase in the number of troubled adults who seek help to uncover memories of childhood abuse that they suspect have been buried by their own brains.

Healing or Hype?

Although there is truth to some of the claims that buried memories cause people’s social problems, skeptical researchers believe that many people seeking lost memories actually find false ones instead. In effect, a psychotherapist can talk someone into creating memories of events that never really happened. For example, says psychology professor and memory expert Elizabeth F. Loftus, “not a single piece of empirical work in human memory supports the authenticity of claims going back to six months of age.” Loftus says research has found “no controlled studies showing an event can be accurately reproduced in memory after a long period of repression.”²⁴

In other words, an infant who is frightened or troubled by something probably will not grow into a frightened or troubled adult with amnesia just because of that one experience. But believers and skeptics alike have a lot of gray area to sift through in studying memory. Very little is known about the causes and effects of amnesia of any type. All that is known is that memory loss does occur, and when it happens, there may be little that scientists or doctors can do to restore the lost memories.

One of the best ways to deal with amnesia is to keep it from happening in the first place. Much of the current work on amnesia is focused on teaching people about common causes of amnesia and how to keep their brains safe from such hardships.