Amnesia

What is Amnesia?

The profound loss of memory in the presence of relatively preserved cognitive abilities

Why is amnesia interesting?

  • By studying a system when it breaks down (e.g. amnesia) we can learn a lot about how that system functions normally (e.g. healthy memory)
  • We need memory to survive
  • Despite some severe memory problems amnesics are able to retain a remarkable range of abilities

Types of Amnesia

  • Psychogenic Amnesia
  • Organic Amnesia
    • Transient
    • Persistent
    • Degenerative
    • Non-degenerative
      • Material Specific
      • Global - The Classic Amnesic Syndrome

Brain Region Involved

The Hippocampus

What’s so important about the Hippocampus

  • Hippocampus placed at the ‘end’ of the primate visual system → Feldman and Van Essen (1991)

Papez’s Circuit

  • Hippocampal Amnesia (Medial temporal Lobe damage, fornix)

  • Korsakoff’s Amnesia (Thaimine Deficiency)

  • (Mammillary bodies, anterior thalamus)

Comme etiologies (causes) of Amnesia

  • Physical Damage → head trauma or surgery
  • Viral Disease → Encephalitis
  • Loss of blood flow → Ischaemia
  • Loss of oxygen → Anoxia
  • Nutritional deficiency → Low Thiamine (Korsakoff’s)

Surgery of Epilepsy → Patient HM (Milner)

Head Trauma → Patient BJ (Van and Aggleton, 2004)

Herpes Encephalitis → Patient EP (Squire)

Functions Spared or Impaired in Amnesia

  • Spared functions
  • Impaired functions
  • Taxonomy of Long term memory
  • Controversies

Spared Functions

  • General cognitive abilities

    • IQ, Language, attention, vision, executive functions Tests:
    • WAIS for IQ attention
    • Wisconsin Card Sorting Test for Executive Function Graded
    • Naming Test for General semantics

  • Short-term memory

    • Tests: i) Digit span ii) Corsi block span
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  • Implicit/procedural memory

    • Tests: Varied.

Procedure Memory

Perceptual Priming

Habit Learning (Knowlton et al, 1996)

  • 'Weather prediction task’

    • Amnesic & Parkinson’s & Huntingtons patients tested

  • Amnesics → normal learning of ‘rule’ over first 50 trials, but can’t recognise specific stimuli.

  • Huntington’s & Parkinson’s patients (striatum damage) → can’t learn rule but can recognise specific stimuli

Impaired Function

  • Impaired Episodic Memory

    • memory for events and episodes which were personally experienced
    • i) Anterograde Amnesia ii) Retrograde Amnesia

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Semantic Memory

  • The ability to remember facts and information independently

‘Declarative’ Taxonomy of Memory → Squire’s

Topic of Controversy

  • Brain regions supporting
    • Recognition memory
    • Semantic memory
  • Memory Consolidation
  • Hippocampus → spatial perception / scene construction

‘Declarative’ Taxonomy of Memory (Revision)

Familiarity vs. Recollection

  • Recollection → Rich detailed remembering of past events
    • E.g. seeing a face and remembering who they are, where and when you last saw them
  • Familiarity → Feeling that something is familiar but no details about it retained.
    • E.g. recognising someone you’ve seen before, but not knowing their name, or who they are

Dissociations between recognition and recall

  • Hippocampus NOT essential for tasks which can be solved by a sense of familiarity

Is the Hippocampus Involved in Semantic Memory

Semantic Memory

  • HM is impaired memory for word definitions (Gabrielli et al., 1988) → Also patient GD. Squire (1992) and others
  • Both episodic and semantic memory affected in amnesia → declarative memory
  • Early onset developmental amnesics → spared semantic memory:
    • neocortex allows slow gradual learning
    • a small fragment of remaining hippocampus supports this function
    • (Vargha-Khadem et al., 1997)

Hippocampus and Memory Consilidation

Temporal Gradients in Retrograde Amnesia

  • Old memories (childhood) still remembered
  • Memories 5-10yrs before lesion lost
  • Forgot death of favorite uncle in 1950
  • Implies hippocampal/ MTL memories ‘consolidated’ in neocortex over time & become independent of the hippocampus (Marr 1971; Alvarez & Squire, 1996)

Testing Retrograde Amnesia

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  • HM:
    • photos of celebrities → retrograde amnesia spans decades, more distant memories relatively preserved
    • (Marslen-Wilson & Teuber, 1975)

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  • PZ:
    • Butters & Cermak (1986) Wrote autobiography Test personal memories

Autobiographical Memory Interview (Kopelman et al., 1990).

Retrograde Amnesia

  • Most amnesics suffer from some some RA

  • High variability in length → case RB a few years → case LD entire life

  • Problems

    • Not often examined in studies
    • Few standardized tests available
    • Low motivation of patients
    • Are all the stimuli as salient across time periods?
    • Have the episodic memories become more semanticized?

Multiple Trace Theory (Nadel and Moscovitch, 1997)

  • Episodic memories are never consolidated completely from the hippocampus, in particular memories for visual-spatial details of events

Role of the Hippocampus in: imagination & scene construction

Impaired Scene Construction

  • Patients can’t imagine the scene

  • But can imagine objects

  • Patients also have problems perceptually processing complex scenes, but not objects (Lee et al., 2005 Hippocampus)

  • Suggestion: the hippocampus is involved in mental scene construction