Amnesia


Contents

Introduction

https://www.youtube.com/watch?v=62R0BsYe0iw

Deficit in memory.


History

French psychologist Theodule-Armand Ribot was among the first scientists to study amnesia. He proposed Ribot’s Law which states that there is a time gradient in retrograde amnesia. The law follows a logical progression of memory loss due to disease. First, a patient loses the recent memories, then personal memories, and finally intellectual memories. He implied that the most recent memories were lost first.

365px-theodule-armand_ribot
Théodule-Armand Ribot (18 December 1839 – 9 December 1916), was a French psychologist, known for Ribot’s Law regarding retrograde amnesia.

Aetiology

3 generalized categories in which amnesia could be acquired by a person:

  • Head trauma (eg. head injuries)
  • Traumatic events (eg. seeing something devastating to the mind)
  • Physical deficiencies (eg. atrophy of the hippocampus)

Other causes:

  • Electroconvulsive therapy
    • Electrically induced seizures for therapeutic effect can have acute effects including both retrograde and anterograde amnesia
  • Alcohol
    • Can cause blackouts and/or deleterious effects on memory formation
    • Korsakoff syndrome

Types

Primary types:

  • Retrograde amnesia
    • Inability to remember things that occurred before a CNS insult.
    • One may be able to encode new memories after the incident.
    • Episodic memory is more likely to be affected than semantic memory.
    • People suffering from retrograde amnesia are more likely to remember general knowledge rather than specifics.
    • Affected brain regions: Hippocampus
    • Cause: Head trauma, cerebrovascular accident, stroke, tumor, hypoxia, encephalitis, or chronic alcoholism.
    • Retrograde amnesia is usually temporary and can be treated by exposing them to memories from the loss.
  • Anterograde amnesia
    • Inability to remember things that occurred after a CNS insult (acquisition of new memory).
    • Long-term memories from before the event remain intact
    • Cause: Long-term alcoholism, severe malnutrition, stroke, head trauma, encephalitis, surgery, Wernicke–Korsakoff syndrome, cerebrovascular events, anoxia or other trauma
    • Affected brain regions: Medial temporal lobe and medial diencephalon.
    • Cannot be treated with pharmacological methods due to neuronal loss.
      • However, treatment exists in educating patients to define their daily routines and after several steps they begin to benefit from their procedural memory. Likewise, social and emotional support is critical to improving quality of life for anterograde amnesia sufferers.

Other types:

  • Post-traumatic amnesia
    • Generally due to a head injury and is often transient, but may be permanent or either anterograde, retrograde, or mixed type.
    • The extent of the period covered by the amnesia is related to the degree of injury and may give an indication of the prognosis for recovery of other functions.
  • Dissociative amnesia
    • Results from a psychological cause as opposed to direct damage to the brain caused by head injury, physical trauma or disease, which is known as organic amnesia.
    • Includes:
      • Repressed memory “Psychogenic Amnesia”
        • Inability to recall information, usually about stressful or traumatic events in persons’ lives, such as a violent attack or disaster
        • Memory is stored in long-term memory, but access to it is impaired because of psychological defense mechanisms.
      • Dissociative fugue “psychogenic fugue” or fugue state
        • ≥ 1 episodes of amnesia in which patients cannot recall some or all of their past and either lose their identity or form a new identity.
        • The episodes, called fugues, result from trauma or stress and are usually temporary and unresolved, and therefore may return.
        • Often manifests as sudden, unexpected, purposeful travel away from home.
      • Posthypnotic amnesia
        • Events during hypnosis are forgotten, or where past memories are unable to be recalled.
  • Lacunar amnesia
    • Loss of memory about one specific event
  • Childhood amnesia or infantile amnesia
    • Common inability to remember events from one’s own childhood.
  • Transient global amnesia
    • Typically amnestic of events more than a few minutes in the past, though immediate recall is usually preserved.
  • Korsakoff syndrome
    • Amnesia (anterograde > retrograde) caused by vitamin B1 deficiency and associated destruction of mammillary bodies.
    • In alcoholics as a late neuropsychiatric manifestation of Wernicke encephalopathy.
    • Confabulations (characteristic)
  • Drug-induced amnesia
    • Intentionally caused by injection of an amnestic drug “premedicant” to help a patient forget surgery or medical procedures, particularly those not performed under full anesthesia, or likely to be particularly traumatic.
    • M/C drugs: 2-halogenated benzodiazepine (midazolam or flunitrazepam)
      • Others: propofol or scopolamine
  • Situation-specific amnesia
    • Can arise in a variety of circumstances (for example, committing an offence, child sexual abuse) resulting in PTSD.
    • Involves a narrowing of consciousness with attention focused on central perceptual details and/or that the emotional or traumatic events are processed differently from ordinary memories.
  • Transient epileptic amnesia
    • Rare and unrecognized form of temporal lobe epilepsy, which is typically an episodic isolated memory loss.
    • Recognized as a treatment-responsive syndrome congenial to anti-epileptic drugs.
  • Semantic amnesia
    • Affects semantic memory and primarily expresses itself in the form of problems with language use and acquisition.

 


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