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Amnesia, its types and causes and difference from dementia

Updated on July 3, 2014

Long term memory is intended for storage of information for a long period of time. It can store a seemingly unlimited amount of information almost indefinitely. The establishment of long term memory involves physical changes in the structure of the neurons in the brain, called long term potentiation. Whenever some thing is learned, circuits of neurons in the brain, called neural network, are created, altered or strengthened. These neural circuits are composed of a number of neurons that communicate with one another through special junctions called synapses. By the process of the creation of new proteins within the body of neurons, and the electrochemical transfer of neurotransmitters across synapse gaps to receptors, the communicative strength of certain circuits of neurons in the brain is reinforced. With repeated use, the efficiency of these synapse connections increases, facilitating the passage of nerve impulses along particular neural circuits.

The consolidation of information from the short term to long term memory involves in changing neural connections for a period of three months or more after initial learning. The hippocampus is essential for processing the new information and its consolidation from short-term to long-term memory. Although it does not seem to store information itself, without the hippocampus new memories are unable to be stored into long-term memory.

Amnesia - Amnesia refers to an inability to recall information that is stored in long term memory. The ability to recall events and information is a very complex brain process. Amnesia refers to a large-scale loss of memories that should not have been forgotten. They may include important milestones in life, memorable events, key people in our lives, and vital facts we have been told or taught. Amnesia occurs in long-term memory when the formerly strengthened synaptic connections among the neurons in a neural network become damaged or weakened, or when the activation of a new network is superimposed over an older one, thus causing interference in the older memory.

Types of amnesia – Basically, there are six types of amnesia –

Ante-grade amnesia – It occurs when there is a brain injury to hippocampus, fornix or mammillary bodies. In this type, the patient is unable to recall events that take place after the onset of amnesia for more than a few minutes. It means that the recent events are not transferred to long term memory. The person’s intelligence, personality and judgment are intact but his day to day functional memory is poor. This can have a devastating effect on the person and his family. However, with the use of memory aids the affected person can, more or less, lead a useful life.

Dissociative amnesia – It is commonly seen in persons, who have witnessed a violent crime or grave accident. It does not occur due to a medical illness. The person doesn’t experience an identity crisis but he tends to pass through a trance like state. The person may develop depersonalization in order to block a stressful experience. Its subtypes are as follows –

  • Generalized amnesia – It involves the person’s whole life.
  • Localized amnesia – There is no memory of a specific traumatic event that happened.
  • Selective amnesia – The person remembers only selective parts of the event.
  • Systematized amnesia – There is memory loss regarding a specific category of information.

Retro-grade amnesia – In this type, the affected person is unable to recollect events that occurred before the amnesia took place. It is caused by a disease or a brain injury in areas linked with episodic memories i.e. hippocampus and median temporal lobes. Memory is poorest of the events that occurred just before amnesia. Early memories are comparatively safe but there is a memory decline building up to the event. There is no cure for this condition so far.

Infantile amnesia – In this type, there is an inability to recall events from early childhood. It is believed to have taken place due to immaturity in certain areas of the brain in the very early stages of development. This clarifies that memories begin to form only when certain parts of the brain are well formed.

Transient global amnesia – In this type, there is temporary impairment of memory in an otherwise healthy person. The person is unable to recall recent occurrences, visuals or verbal information for more than a couple of minutes. The memory loss usually does not last for more than a day but the experience can be frightening. Some may experience headache, dizziness and nausea along with memory loss. The person is unable to remember what occurred during the period of memory loss.

Its incidence is 3.4 to 5.2 people per 100,000 per year and the condition mostly affects 50-80 year olds. The causes of transient global amnesia may include the following –

  • Emotional stress
  • Strenuous physical exertion
  • Basilary artery migraine
  • Transient ischemic attack (mini stroke)

Wernike Korsakoff’s psychosis – This is progressive disorder caused by the prolonged alcohol abuse. It is usually accompanied by neurological dysfunctions like loss of co-ordination during movement or numbness in fingers and toes. It is also associated with thiamine deficiency due to malnutrition.

Blackout phenomenon – Amnesia is caused by a bout of heavy drinking, in which the person cannot remember what had happened during the period of his or her binge.

Hysterical amnesia – It is retro-grade amnesia. It does not depend on an actual brain disorder past or present. It involves failure to recall particular past events or those falling within a particular period of person’s life. Another type of hysterical amnesia is essentially ante-grade amnesia, in which there is a failure to register and recollect the current events in person’s life. Rarely, amnesia appears to cover the person’s entire life, extending to his or her identity, whereabouts and circumstances. Although such cases are extremely rare, they are seldom wholly convincing. They usually clear up with relative rapidity, with or without psychotherapy.

Causes of amnesia – Amnesia can result from any damage to the brain structures like limbic system that controls emotions and memories. It includes thalamus lying deep within the centre of the brain and hippocampus situated within the temporal lobes of the brain. The following are some important causes of amnesia –

  • Stroke
  • Brain inflammation (encephalitis)
  • Tumors in the area controlling memory
  • Lack of adequate oxygen in the brain, for instance, from heart attack, respiratory distress or carbon mono-oxide poisoning
  • Long term alcohol abuse
  • Degenerative brain diseases such as dementia and Alzheimer’s disease
  • Seizures
  • Electroconvulsive therapy
  • Some medications like benzodiazepines
  • Head injuries
  • Emotional shock or trauma such as being the victim of a violent crime

Symptoms of amnesia – They include the following –

  • Impaired ability to learn new information after the onset of amnesia as in ante-grade amnesia
  • Impaired ability to recall past events and previously familiar information as in retrograde amnesia
  • False recollections (confabulation), either completely invented or made up of genuine memories misplaced in time
  • Confusion or disorientation
  • Neurological symptoms such as uncoordinated movements, tremors or seizures

How is dementia different from amnesia? – Dementia differs from amnesia in the following feature -

  • Dementia is a general term to describe symptoms such as impairments of memory, communication, focus and thinking. There is a problem with at least two brain functions such as memory loss, impaired judgment, impaired focus or language.
  • The changes are often subtle and tend to involve short-term memory. The elderly person may be able to remember years past, but not what he or she had for breakfast. The changes in short-term memory include forgetting where they left something, struggling to remember why they went into a particular room. It causes inability to perform some daily activities such as paying bills etc.
  • A person with dementia struggles to communicate thoughts to others. This means that a person with dementia can’t explain things. They may reach for the right words, but just can’t seem to grasp them. A conversation with such a person becomes difficult and it takes longer than usual to conclude.
  • In dementia patients, the changes in mood are quite common. Depression is typical of early dementia. Another common symptom of early dementia is listlessness or apathy. Dementia patients lose interest in hobbies and activities like spending time with friends and family.
  • There may be signs of confusion in the early stages of dementia, which can occur for a number of reasons.
  • They forget the meaning of the words they hear. Struggling to follow along with conversation or TV programs is a classic early sign.
  • Sense of direction or spatial orientation starts to deteriorate with the onset of dementia. The patients can not recognize once familiar places and forget regularly used directions.
  • They may repeat daily tasks like shaving or collecting items obsessively. They may repeat the same question in a conversation that has been answered.
  • They have difficulty in adjusting to changes, which may become a frightening experience.
  • There may be noticeable changes in their personality, due to which they find it difficult to adjust in a social setup, even if it is familiar one.

Highlights to recall –

  • Amnesia is an inability to recall information stored in the long term memory, which takes place on a large scale.
  • In ante-grade amnesia, the patient is unable to recall events that take place after the onset of amnesia for more than a few minutes. On the other hand in retro-grade amnesia, the patient is unable to recall events that took place before the onset of amnesia. The dissociative amnesia may occur in persons who have witnessed personally a violent crime or a grave accident taking place. The person may develop a state of depersonalization in order to block the terrifyingly stressful experience.
  • In transient global amnesia, the person is unable to recall events for a few minutes. The memory loss usually does not last for more than a day but it is a frightening experience for the affected person. This condition mostly affects 50 to 80 years old persons. Wernike Worsakoff’s psychosis occurs in individuals, who suffer from prolonged alcohol abuse. The condition is usually accompanied by neurological dysfunctions like loss of co-ordination during movement or numbness in fingers or toes.
  • The hysterical amnesia is a retro-grade one. It involves failure to recall particular past events or those falling within a particular period of person’s life. Another type of hysterical amnesia is essentially ante-grade amnesia, in which there is a failure to register and recollect the currents events in person’s life. Although such cases are extremely rare, they usually clear up with relative rapidity, with or without psychotherapy.
  • In amnesia, there may be false recollections, either completely invented or made up of genuine memories misplaced in time.
  • Amnesia may be associates with neurological symptoms such as uncoordinated movements, tremors or seizures. There may be accompanied confusion or disorientation.
  • Dementia generally involves impairment of memory, communication, focus and thinking, having a problem with at least two of them. The changes are often subtle and tend to involve short-term memory. The affected person may be able to remember years past, but not what he or she had for breakfast.
  • A person with dementia struggles to communicate thoughts to others. This means that a person with dementia can’t explain things. They may reach for the right words, but just can’t seem to grasp them.
  • Sense of direction or spatial orientation starts to deteriorate with the onset of dementia. The patients can not recognize once familiar places and forget regularly used directions.
  • There may be noticeable changes in their personality, due to which they find it difficult to adjust in a social setup, even in a familiar one.
  • It can make the person confused and unable to remember people and names. The persons can’t seem to explain things. They may reach for the right words, but just can’t seem to grasp them. Conversations with an elderly parent who.
  • There are changes in the personality and social behavior of an individual suffering from dementia.









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    • Dana Tate profile image

      Dana Tate 2 years ago from LOS ANGELES

      Thank you for this information Dr. I have an aunt who had a very traumatic child- hood and I remember she had to take medication which she stopped because she started hallucinating. Now she can't recall many of her child-hood memories. When we have family get-together's and we talk about our past she doesn't recall those same memories.

    • Dr Pran Rangan profile image
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      Dr Pran Rangan 2 years ago from Kanpur (UP), India

      Thanks for reading my hub. Amnesia and dementia are real problems both for the affected person as well as care-givers.

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