amnesia - what is it? a selective disruption of the processes underlying long-term memory ...

Amnesia - What is it?

A selective disruption of the processes underlying long-term memory

Short-term and sensory memory are typically functional

Other cognitive functions are not impairedIntelligence, attention...

Recency vs Primacy

• Amnesia patients exhibit recency effect but not primacy effect

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Long-termmemory

Short-termmemory

Amnesia - What is it?

A selective disruption of the processes underlying long-term memory

Short-term and sensory memory are typically functional

Other cognitive functions are not impairedIntelligence, attention...

Retrograde & Anterograde

• Retrograde amnesia - Loss of information that was learned before the onset of amnesia

• Anterograde amnesia - inability to learn new information after the onset of amnesia

• Both can occur in the same patient and commonly do

Causes of Amnesia

• Concussion• Migraines• Hypoglycemia• Epilepsy• Electroconvulsive shock therapy• Specific brain lesions (i.e. surgical removal) • Ischemic events• Drugs (esp. anesthetics)• Infection• Psychological• Nutritional deficiency

Types of memory

Fact memory Skill memory

Declarative Non-declarative (Procedural)

Memory Habit

Explicit Implicit

Knowing that Knowing How

Cognitive mediation Semantic

Conscious recollection Skills

Elaboration Integration

Memory with record Memory without record

Autobiographical Perceptual

representational Dispositional

Vertical association Horizontal association

Locale Taxon

Episodic Semantic

Working Reference

Proposed types of memory

Brain regions associated with human amnesia

• Diencephalic amnesia - damage to the medial thalamus and mamillary nuclei

• Medial temporal lobe amnesia - damage to the hippocampal formation, uncus, amygdala, and surrounding cortical areas

Diencephalic Amnesia

• Damage to the medial thalamus and/or mamillary bodies– stroke

• Korsakoff’s syndrome– Caused by thiamine

deficiency as a result of chronic alcoholism

Korsakoff’s symptoms

• Anterograde amnesia• Retrograde amnesia

– Covers most of the adult life

• Lack of insight– Typically unaware of memory

problems

• Confabulation– Patient makes up stories to fill

in the past

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Medial Temporal lobe amnesia

• Hippocampus is most important site of damage

Case H.M.

• Epileptic patient

• Had medial temporal lobes removed to stop seizures

• Seizures were reduced but H.M. became severely amnesiac.

Case H.M.

• His intelligence is above normal– IQ = 112

• Performs normally on all tests of short-term memory

• Selective long-term memory impairment

Case H.M.



Control brain H.M.

Case H.M.

• Memory impairment for recent events– spans the 3 years prior to his surgery

• Capable of recalling childhood memories• Anterograde amnesia was initially thought

to be global (all types of memory)• later discovered that certain types of

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Case H.M.

• Grave memory impairment for recent events– spans the 3 years prior to his surgery

• Capable of recalling childhood memories• Anterograde amnesia was initially thought

to be global (all types of memory)• later discovered that certain types of

learning are intact

Case H.M.

• Priming still works

• H.M. can still form procedural memories

Case H.M.• The Gollin incomplete picture test

– subjects asked to identify the object– pictures are shown in sequence from least to

most clear– shown the same images at a later date– both amnesiacs and control subjects identify the

object at an earlier stage









Case H.M.

• Mirror drawing task.– Trace figure while looking in a mirror– Control subjects get better at this with repetitive

training.



Case H.M.

• Mirror drawing task– H.M. improved with

repeated training.

– Procedural memory is intact

– He cannot recall ever having performed this task before 0

10

20

30

40

Attempts each daynumber of errors per attempt

Day 1 Day 2 Day3

Case H.M.

– Doesn’t remember the death of his father– Can’t remember or describe his job– Doesn’t remember his examiners

Case H.M.

• According to our memory dichotomies, what type of memory is the medial temporal lobe (especially the hippocampus) responsible for?

Types of memory

Case H.M.

• H.M.s Retrograde amnesia is temporally graded– remote memory is spared but recent memory is lost

• Not all amnesia patients show this pattern– V.C., N.A. have extensive retrograde amnesia (flat

gradient)

Memory recall ability

Recent Remote

Age of memory

recall performance

H.M.

Control

N.A.

Lessons from amnesia

• Existence of Multiple memory systems

• Localization of cognitive functions

S.• “Photographic” extreme memory ability (a

mnemonist)

• Able to recall complex test stimuli

S.

• “Photographic” extreme memory ability (a mnemonist)

• Able to recall complex test stimuli • S. used two “strategies” or abilities typical of

mnemonists:– rich synesthesia-like quality to his perception of stimuli

- leads to stronger associative links– vivid and elaborate mental imagery of things he should

remember

S.

• “ Even numbers remind me of images. Take the number 1. This is a proud, well-built man; 2 is a high-spirited woman; 3 a gloomy person (shy, I don’t Know); 6 a man with a swollen foot...”

Luria, A.R. The mind of a mnemonist. 1968

Luria, A.R. The man with a shattered world. 1972

amnesia - what is it? a selective disruption of the processes underlying long-term memory ...

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