What is amnesia (amnesiac syndrome)?

Amnesia is a dramatic form of memory loss. If you have amnesia you may be unable to recall past information (retrograde amnesia) and/or hold onto new information (anterograde amnesia). Amnesia, in the Greek language, means “forgetfulness.” However, amnesia is far more complicated and severe than everyday forgetfulness. Forgetting what your spouse asked you to pick up at the grocery store is “normal.” Forgetting that you are married can be a sign of amnesia.

Amnesia is often portrayed in movies and TV shows. What soap opera hasn’t had a storyline involving it? Fictional characters with amnesia often lose their entire identities. They can’t even remember their names. Fortunately, amnesia usually isn’t that severe in real life.

How does memory work?

Memory is the ability to hold onto (retain) and recall information from the past. There are three stages of memory: encoding, storage and retrieval.

  • Encoding: The brain receives new information and creates a series of connections to represent that information. Those connections may link to other information already stored in your memory. For many types of information, you have to be paying attention to accurately encode the information.
  • Storage: Those previously formed connections are maintained in your brain, even though you may not be using them.
  • Retrieval: The brain recreates or activates the connections that represent previously encoded information and you can recall or recognize that information from the past.

This is a simple description of how memory works. Keep in mind that these stages and the processes within them are imperfect. Memory itself is imperfect. The witness to a robbery might remember a blue shirt when the robber was actually wearing green. Such forgetfulness is just that — forgetfulness — not necessarily a sign of amnesia.

There are several types of memory. Here are the two most relevant to understanding amnesia:

  1. Declarative/Explicit: Knowledge of facts and events in everyday life. Amnesia can erase these memories.
  2. Nondeclarative/Implicit: Non-conscious knowledge. Amnesia will not erase these “ingrained” memories. If you have amnesia, you should still remember how to walk or ride a bike.

The brain areas involved in memory are different depending on the type of memory you are forming and how long it can be stored.

  • Short-term memory: Your short-term memory lasts as long as you have the information ‘in mind’ – usually between five seconds and 30 seconds. During that time you’re able to juggle an average of seven pieces of information – for example, seven letters, seven words or seven numbers. The frontal and parietal lobes are important for this type of memory.
  • Long-term memory: Your long-term memory lasts between a minute and a lifetime. In theory, there’s no limit to your long-term memory. However, there is a limit to your ability to recall that information. The hippocampus and surrounding temporal lobes of the brain are important areas for long term storage and retrieval of information. However, long-term memory involves many areas of the brain and damage to many different parts of the brain can cause amnesia.

How common is amnesia? Who gets it?

Amnesia can occur in many common neurological disorders like Alzheimer’s disease and other forms of dementia, stroke and traumatic brain injury, as well as other systemic illnesses that affect the brain.

Are there different types of amnesia?

There are many different names for amnesia and amnesia syndromes. Here are a few common terms you may encounter:

  • Retrograde Amnesia: Describes amnesia where you can’t recall memories that were formed before the event that caused the amnesia. It usually affects recently stored past memories, not memories from years ago.
  • Anterograde Amnesia: Describes amnesia where you can’t form new memories after the event that caused the amnesia. Anterograde amnesia is far more common than retrograde.
  • Post-traumatic Amnesia: This is amnesia that occurs immediately after a significant head injury. It may involve retrograde amnesia, anterograde amnesia, or both.
  • Transient Global Amnesia: A temporary syndrome where you experience both retrograde and anterograde amnesia. Memory loss is sudden and only lasts up to 24 hours.
  • Infantile Amnesia: This is the term used to describe the fact that people can’t recall memories of events from early childhood. Few people have memories from before the ages of three to five because the brain areas that support memory are still developing.
  • Dissociative Amnesia/Psychogenic Amnesia: A mental health disorder where you experience amnesia after a significant trauma. You block out both personal information and the traumatic incident from your memory.

Is amnesia real?

Yes, but it is rarely as it is portrayed in movies and TV shows. Typical patients don’t lose their entire identities.

What causes amnesia?

Amnesia causes are divided into two categories: neurological and functional. Here are some of the most common causes.

Neurological Amnesia.

Brain injuries:

  • Trauma from a car crash, sports, a fall from a ladder, penetrating object (i.e.,bullet), etc.

Brain diseases:

  • Alzheimer’s disease and other dementias.
  • Stroke.
  • Seizure.
  • Brain tumor.

Brain infections:

  • Encephalitis.
  • Lyme disease.
  • Syphilis.
  • HIV/AIDS.

Other:

  • Anoxia (lack of oxygen).
  • Cardiac arrest.
  • Thyroid issues.
  • Chronic alcoholism.
  • Vitamin B1 (thiamine) or B12 (cyanocobalamin) deficiency.
  • Radiation.

High levels of corticosteroid.

Functional/Psychogenic/Dissociative Amnesia.

Functional amnesia, a psychiatric disorder, is rarer than neurological amnesia. It is not associated with any known brain trauma or disease but rather appears to occur because of an emotional trauma. This is usually retrograde amnesia (inability to remember past information). Occasionally, it is so severe that the person may forget their own identity.

Does amnesia erase the person’s identity?

Only in very rare, very severe cases of functional amnesia.

How long does amnesia last? Is amnesia permanent?

Amnesia can be:

  • Temporary, such as after a head injury as your brain heals.
  • Permanent and unchanging, such as after a serious disease like encephalitis or a stroke.
  • Progressive or slowly getting worse, such as from progressive diseases like dementia.

Are amnesia and Alzheimer’s/dementia the same?

They are not the same. Amnesia is a symptom while dementia is a disease. Think of this like the relationship between a fever (the symptom) and the flu (the illness). Alzheimer’s is one type of dementia.

Is Mild Cognitive Impairment (MCI) the same as amnesia?

No, MCI is not amnesia. MCI is a diagnosis that means that there has been a slight decline of memory or other thinking skills that does not interfere with daily life. Some 15% to 20% of adults ages 65 and over have MCI.

Do patients with amnesia lose their motor skills?

Motor skills are nondeclarative. People with amnesia don’t lose learned motor skills – skills that require coordinated movement of muscles. “Just like riding a bike” is an old saying that means the learned activity is “second nature” — easy to remember and repeat. In fact, studies by neurologists have proven that people with amnesia learn motor skills at the same rate as healthy individuals.

Does amnesia change the patient’s personality?

No. Personality change may happen when the areas of the brain that control personality and behavior are also damaged.

Do people who have amnesia have a shorter attention span?

No. They’re forgetful, but that doesn’t mean they’re not paying attention to the extent that they did before the event that caused the amnesia.

Is amnesia common when a person is drinking alcohol?

Alcohol can stunt the brain from developing new memories. Two types of memory events can happen to heavy drinkers: blackouts and amnesia.

Heavy alcohol abusers who have poor diets are at risk of developing Wernicke-Korsakoff syndrome. Wernicke-Korsakoff syndrome (alcoholic amnesia) affects 1% to 3% of the population, often people who are between 30 years old and 70 years old. Researchers have concluded that alcohol prevents the body from processing the nutrient B1, a vitamin vital to memory. The damage done to the brain by alcoholic amnesia is permanent in 80% of cases. This alcohol-induced syndrome includes a severe anterograde amnesia or ability to form new memories. Patients may also confabulate or ‘make up’ highly unusual memories.

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