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

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

    • 

• 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

• 

  

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

• HM:

  • photos of celebrities → retrograde amnesia spans decades, more distant memories relatively preserved

    • (Marslen-Wilson & Teuber, 1975)

• 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