How Amnesia Works


Clive Wearing and his wife, Deborah, pictured on the cover of her memoir about his amnesia.
Photo courtesy Amazon.com

Imagine waking up in your bedroom with no idea of where you are. Something feels familiar about the cotton sheets, the pictures on the wall, the sheer curtains, but you can't place it. Minutes later, you feel that same sensation of waking up, but this time you're standing at your dresser, wearing a T-shirt and jeans with no recollection of ever having been in bed. It's as though your consciousness lacks a past and a future, like a stop-motion film in which every previous frame is destroyed.

Clive Wearing lives in that perpetual present. The British musician and musicologist has the worst case of amnesia ever recorded [source: Sacks]. His memory span lasts a few seconds before it washes away in the blink of an eye and starts anew. Triggered by a case of herpes encephalitis, which infects the brain and causes it to swell, Wearing's amnesia has left him in a state of constant awakening in which every kiss, conversation or cup of coffee is his first.

The encephalitis eroded Wearing's ability to make new memories, severing any recollection of the recent past. According to a New Yorker profile on him, something as simple as eating an apple would seem almost like a magic trick in Wearing's mind. One moment, he holds a whole apple in his hand. The next, there's nothing left but the core.

Unlike most amnesia cases in which older memories are preserved, much of Wearing's long-term episodic memory of specific facts and events disappeared. His motor skills and general intelligence remain intact; it's the memory of using them that's disconnected. For instance, Wearing still plays the piano proficiently, but he wouldn't remember doing so, much less what song he played.

The nuances of his fragmented memory reflect the complexity of amnesia and the human brain. Wearing has always remembered his wife, Deborah, yet cannot immediately recall the name of his favorite composer, Lassus [source: Sacks]. In conversations about his life, Wearing can expound on some events; however, it is sometimes unclear whether his stories spring from true memories or his imagination [source: Sacks].

So how did amnesia erase Wearing's memory like a blackboard? And is having a perfect memory that great? Go to the next page to find out and to stroll down memory lane.

The Process of Memory From Perception to Retrieval

Primary regions of the brain where memories are made and stored.
Primary regions of the brain where memories are made and stored.
HowStuffWorks 2008

Imagine for a moment what life would be like with a perfect memory. If you could remember each detail of everything taken in by your five senses, the first hour of the day would be mentally overwhelming -- truly too much information. That is why the brain sorts all of that data into your short-term memory or long-term memory or discards it.­

Short-term memory allows us to retain information we need in the moment and then get rid of it. It's the mental equivalent of a takeout box. You use it to temporarily store small amounts of information and toss it afterward. Likewise, the short-term memory holds up to seven pieces of information for about 20 to 30 seconds [source: Canadian Institute of Neurosciences, Mental Health and Addiction]. Long-term memory is more like your internal freezer. It can hold information for years, or even a lifetime, but without some use, stuff in there can get "freezer burned."

­­We make and store memories by forging new neural pathways to the brain from things we take in through our five senses. The stimuli that our nerve cells detect, such as hearing a gunshot or tasting a raspberry, are called sensory memories. That sensory information flows along the nerve cells as an electrical impulse. As that impulse reaches the end of a nerve, it activates neurotransmitters, or chemical messengers. Those neurotransmitters send the message across the spaces between nerve cells called synapses and move it along to the neurons, or brain cells. If we need to immediately use that sensory information, it moves to the short-term memory, for example, when we hear a phone number and have to remember it to dial.

To turn short-term memories into long-term ones, our brains must encode, or define, the information. Remember that raspberry? Encoding it would likely include cataloging the fruit's size, tartness and color. From there, the brain cells would consolidate the information for storage by linking it to related memories. During this process, that neural pathway strengthens because of the brain's plasticity. Plasticity allows the brain to change shape to take in new information and, thus, new pathways.

Long-term memory retrieval requires revisiting the nerve pathways the brain formed. The strength of those pathways determines how quickly you recall the memory. To reinforce that initial memory, it must move multiple times across the nerve cells, retracing its steps.

Memory formation largely occurs in the brain's limbic system, which regulates learning, memory and emotions. The cortex is the temporary storage place of short-term memories and the area where the brain puts the new stimuli into context. The hippocampus then interprets the new information, associates it with previous memories and determines whether to encode it as a long-term memory. Next, the hippocampus sends the long-term memories to different areas of the cortex, depending on the type of memory. For instance, the amygdala houses intensely emotional memories. The memories are then stored in the synapses where they can be reactivated later.

Next, we'll see what happens when those neural pathways that make our memories are cut off by a roadblock called amnesia.

Neurological Amnesia

Forgetfulness is like taking out the trash. By doing so, you keep the house clean, but occasionally you throw away some useful information, like a receipt or a bill. Likewise, forgetting frees our brains of excessive information, but we sometimes mentally misplace people's names or where we put the remote control because our brains didn't encode the information as discussed earlier.

Now imagine what would happen if instead of picking up and throwing away trash by hand, you used a huge vacuum cleaner. It would suck up almost everything in its path, swallowing your magazines, photos and books. When it comes to memories, amnesia acts like that vacuum cleaner. It's an extreme form of forgetfulness that gets rid of more memories than the brain normally discards. The amount and type of memory eliminated depends on the cause of amnesia.

The kind of amnesia portrayed most often in television and movies is neurological, or organic, amnesia. Neurological amnesia is caused by damage to the areas of our brain that create memories: the cortex — particularly in the temporal lobe — and the hippocampus. These parts of the brain make those neural pathways that convert brief sensory memories to long-term ones, as mentioned earlier. When this kind of amnesia occurs, it's like cutting a telephone line. To the person at the end of the receiver, there is no information because there is no cord for it to pass through.

If there is no pathway for the information to travel across, the brain cannot form new memories or retrieve some old ones. The severity and specific location of the damage determine the extent and length of the amnesia. A brief loss of oxygen flow to the brain, for instance, may leave someone unable to remember only a few hours.

There are several causes of neurological amnesia, according to the Mayo Clinic, including:

  • Head injury
  • Tumor
  • Stroke (when blood flow to the brain stops)
  • Viral infection (such as herpes encephalitis)
  • Brief loss of blood or oxygen flow to the brain
  • Electroconvulsive therapy (ECT -- used to treat severe depression)
  • Alcohol abuse causing a thiamine deficiency

Clive Wearing's extreme case of amnesia caused by herpes encephalitis is an example of neurological amnesia. The herpes encephalitis destroyed his hippocampus and parts of his temporal lobe in the brain's cortex. Think back to the telephone. The hippocampus basically acts like the cord and the synapses in the cortex are voicemail messages. Since the hippocampus, or telephone cord was destroyed, Wearing's brain couldn't consolidate new information, giving him an incredibly short memory span. The damage to his cortex was like erasing all of his oldest voicemail messages, affecting his long-term memory as well.

Next, we'll look at how traumatic events can lead to amnesia.

Dissociative Amnesia

Serious car crashes can trigger a case of dissociative amnesia.
Serious car crashes can trigger a case of dissociative amnesia.
Brian Stablyk/Getty Images

People involved in a serious car crash or victims of violent crimes sometimes cannot remember the incident. When amnesia follows an external traumatic event like this, doctors call it dissociative, or psychogenic, amnesia. This type of amnesia links outside events, such as marital problems or financial crises to the neurological reactions in the brain. Like neurological amnesia, dissociative amnesia alters the brain's ability to form new memories. Dissociative amnesia, however, is usually temporary.

Dissociative amnesia splits into two main categories based on the scope of the memory loss. Global dissociative amnesia affects autobiographical information gathered over a long period, whereas situational dissociative amnesia involves memories of particular traumatic events, such as a car accident or violent crime. Both result from the effects of extreme stress on the brain.

Intense, prolonged stress can lead to dissociative amnesia because it activates our adrenal glands, which release cortisol and other hormones into the bloodstream. Cortisol in particular reduces the brain's plasticity, or ability to change shape to form new nerve pathways during memory formation. Extended exposure to cortisol can negatively affect the hippocampus [source: Canadian Institute of Neuroscience, Mental Health and Addiction]. It is harder to make memories with an impaired hippocampus, possibly producing dissociative amnesia at the climax of the stress.

For example, a woman walks into a hospital looking confused and acting as though she has completely lost her identity. In a few days, something triggers her memory. Maybe she sees something on the news about her hometown or hears her daughter's name in a conversation. From there, she quickly recalls who she is and recovers from the strange behavior.

Although very rare, that woman likely was suffering from global dissociative amnesia leading to a fugue state, or period of wandering. This type of amnesia, which deals with the loss of all autobiographical information and identity, is so severe because most patients have mental health problems that worsen the effects of the psychological trauma experienced. Often they have dealt with prolonged depression and former brain damage, as well as epileptic seizures or a head injury across a larger area of the brain. Therefore, the trauma can have a greater, more widespread impact on the brain.

Amnesia doesn't always wipe out your past. Sometimes it obliterates your future. Read on to find out how.

Anterograde Amnesia

Lik­e any medical condition, amnesia's causes and effects can be hard to pin down. For one person, it may erase a few minutes' worth of memory. For another, like Clive Wearing, a whole lifetime might disappear. So in addition to defining amnesia by the cause — brain damage or psychological trauma — doctors characterize amnesia by the type of memories lost.

Retrograde amnesia means you have trouble remembering the past. Oppositely, anterograde amnesia means you have difficulty making new memories and absorbing new information.

Anterograde amnesia, the more common of the two, is associated with injury to the hippocampus. With it, you cannot convert new sensory information into long-term memories. For instance, alcohol-induced blackouts are a type of anterograde neurological amnesia. Drinking too much alcohol blocks the neural pathways in the brain from forming new memories while intoxicated. People experiencing a blackout may talk and interact normally, but the next morning all will be blank.

­

Retrograde Amnesia

A stranger even to yourself? Not quite. Retrograde amnesia doesn't steal your identity.
A stranger even to yourself? Not quite. Retrograde amnesia doesn't steal your identity.
Image Source/Image Source/Getty Images

Retrograde amnesia targets your most recent memories first. The more severe the case, the farther back in time the memory loss extends. This pattern of destroying newer memories before older ones is called Ribot's law. It happens because the neural pathways of newer memories are not as strong as older ones that have been strengthened by years of retrieval. Retrograde amnesia usually follows damage to areas of the brain besides the hippocampus because long-term memories are stored in the synapses of different brain regions. For example, damage to Broca's area, which houses language information, would likely cause language-related memory loss.

With both anterograde and retrograde amnesia, it is important to understand that people's explicit, or episodic, memory is normally what's lost. Amnesia patients retain their personality and identity, along with their implicit, or procedural, memory. That's because your motor skills and instinctive physical memories -- like riding a bike -- are stored separately from your episodic memories. The hippocampus initially processes both types, but episodic memories move to the cortex, while procedural ones go to the cerebellum.

That's why Clive Wearing can still play the piano (implicit memory), but probably can't describe his first recital (explicit memory).

Read on to find out how people with huge holes in their memories carry on with their daily lives.

Living with Amnesia

Living with amnesia focuses on building habits to follow rather than relying on medical remedies. To cope with his extreme amnesia, Clive Wearing began keeping a journal after the onset of illness in 1985. Since his memory lasts only a few seconds, writing allowed him to retain some record of the past, although he never explicitly remembers doing it. Most entries are brief, guided by his implicit, or habitual, memory of how to write and instinctual awareness of keeping the journal.

Although Wearing's knowledge of specific facts and recent events is nonexistent, his IQ has stayed close its pre-amnesia levels, as with other amnesia patients. For instance, if you ask Wearing for directions to the kitchen, he wouldn't be able to tell you. But if you ask him to make you a cup of tea, he can walk to the kitchen and do it independently. Because the implicit and semantic memories, which control performance and motor skills, reside in different areas of the brain from episodic memory, intelligence isn't severely affected.

Unfortunately, there is no magic pill or surgery that can fully restore the lost memories of someone with persistent amnesia. Since neurotransmitters play a large role in memory creation, researchers are investigating the potential of isolating them for treatments. With amnesia caused by alcoholism (Korsakoff's syndrome), vitamin B1 supplements can help stop brain deterioration. Psychotherapy can also aid people with dissociative amnesia by working through the traumatic event. However, most persistent amnesia cases that deal with disease or injury-related brain damage depend on coping, not cures.

Since the bulk of amnesia cases involve anterograde amnesia, treatment focuses on ways to retain new information and build habits through your implicit memory, as we see with Wearing. In this way, you can think of memories as expiring coupons -- either use them or lose them. By integrating memory tools into everyday life, amnesia patients can recall memories as often as possible to try to strengthen them. Amnesiacs manage to remember to use these memory tools by creating habits, or implicit memories, so they instinctively know to check their calendar in the morning for appointments, for instance.

Pocket calendars or PDAs, such as PalmPilots, BlackBerries and iPhones, can be helpful since people with amnesia can program reminders, store large amounts of information and take it everywhere. Having simple data like this on hand can increase the patient's sense of independence and lighten the burden on caretakers. In addition, establishing patterns of living are integral for amnesia patients to get on with daily life.

Read on to find out how amnesia is medically detected and how it can sometimes be prevented.

Amnesia Detection and Prevention

An MRI of a normal brain. MRIs and CAT scans can reveal parts of the brain that may be contributing to symptoms of amnesia.
An MRI of a normal brain. MRIs and CAT scans can reveal parts of the brain that may be contributing to symptoms of amnesia.
UHB Trust/Getty Images

For Clive Wearing, it all started with a headache. A couple of days later, he couldn't remember his daughter's name. A week later, the downhill spiral began in earnest as the herpes encephalitis started to destroy his short- and long-term memories. Although amnesia may seem to be an obvious disease, if it results from a viral infection, there are specific symptoms to watch out for.

According to the Mayo Clinic, people suspected of having neurological amnesia are screened for the following:

  • Whether they can form new memories
  • Their ability to recall past events
  • Imaginary events told as fact, also called confabulations
  • Uncoordinated movements or tremors
  • Confusion and disorientation

­Verbal questioning can be helpful for an initial evaluation, but brain-imaging technology is also beneficial, particularly for people who have had brain injuries. MRIs and CAT scans can reveal parts of the brain that may be contributing to the symptoms of amnesia.

Since neurological amnesia stems from a brain injury, there are a few precautions you take in your daily life. One, wear a helmet when riding a bicycle or motorcycle to protect your head. Two, drink alcoholic beverages in moderation to avoid amnesia caused by alcohol abuse. Finally, for conditions that can trigger amnesia, such as stroke and lack of oxygen or blood to the brain, see your doctor immediately.

Neurological amnesia can also be a symptom of something else. Early signs of amnesia could act as a precursor to Alzheimer's Disease or mild cognitive impairment. Both are forms of dementia, which produces memory loss along with the loss of cognitive skills. Dissociative amnesia can also point to dissociative disorders. Although dissociative amnesia is often temporary, it could be linked to something more serious, such as multiple personality disorder in which people seem to take on alternate identities when triggered by stress.

Next, we'll look at where and why this life-altering condition holds an enduring place in popular culture.

Amnesia in Pop Culture

Anna Anderson claimed that she was Anastasia, daughter of Tsar Nicholas II of Russia.
Anna Anderson claimed that she was Anastasia, daughter of Tsar Nicholas II of Russia.

Hollywood loves leading characters with amnesia. Since the days of silent film, attractive stars have hit their head, fallen unconscious and woken up with no memory of their life or identity. Later -- usually after discovering a newfound appreciation for life -- they're hit on the head again and the amnesia is cured. It's an entertaining scenario, but nearly impossible. Although some scripts are more realistic than others, comedies, thrillers and action movies have used amnesia as a plot device. The following recent popular films provide a sampling of Hollywood's love affair with memory loss:

  • "Eternal Sunshine of the Spotless Mind"
  • "Mulholland Dr."
  • "Memento"
  • "Vanilla Sky"
  • The Bourne Trilogy

Aside from film, the amnesia theme constantly pops up in popular culture. Sudden cases of amnesia are classic soap opera fodder. On the more intellectual end of the cultural spectrum, authors including Charles Dickens (in "A Tale of Two Cities") have worked amnesia into their novels. Even rock band Radiohead called their 2001 album "Amnesiac." Book critic for Time magazine, Lev Grossman, describes Americans' cultural obsession with amnesia as a "national tradition" [source: Grossman]. He says the concept of the American dream is based on a metaphorical amnesia in which people leave behind their former lives to achieve success.

Maybe it's the mystery of amnesia that makes it appealing to watch and read about. Memory is our only personal record of the past and of who we are as individuals. In this way, it links our pasts to our futures. But while erasing your history may seem appealing, true cases of amnesia prove that starting over in the brain is a delicate, complicated process. To read more about mind and memory, check out the links on the next page.

Related Articles

More Great Links

Sources

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