Lecture 4 - Memory Disorders Flashcards
What are the 2 causes of amnesia?
Organic: Acute damage to the brain, or degenerative disease
Psychogenic: Purely psychological
What are the 2 forms of amnesia?
Retrograde: You lose memories in the lead up to having the amnesia
Anterograde: Difficulty forming/consolidating new memories
What are the 6 main features of the amnesic syndrome (‘pure’ amnesia)?
- Pronounced anterograde amnesia (inability to encode/retrieve memories for events encountered after the onset of amnesia)
- Variable retrograde amnesia (inability to retrieve memories acquired before the onset of amnesia)
- Intact STM
- Preserved general intelligence
- Skills such as driving and playing music unaffected
- Some residual learning capacity
What parts of the brain are important for memory?
Amygdala (emotional content of episodic memories)
Basal ganglia (important for learning motor skills)
Cerebellum (memory for automatised skills - both motor and cognitive)
Frontal lobes
Occipital lobes
Describe the case of HM to show the effects of damage to the hippocampus
- Post surgery (removed 2/3 of the hippocampus) unable to encode/retrieve new episodic memories
- HM had developed severe anterograde amnesia
- Also developed retrograde for the period 10-15 years prior to operation
- Still had normal STM & learning of new procedural memories
Describe Korsakoff’s syndrome
- Caused by thiamine deficiency (usually due to chronic alcoholism)
- Damage to diencephalon (regulates activity in PFC)
- Patients often appear to be drunk
Describe amnesia in Korsakoff’s syndrome
- STM normal
- Encoding/retrieval of new episodic LTM impaired
- Retrograde amnesia stretching back years or decades
- Temporal gradient of retrograde amnesia: recall for events in the time immediately leading up to its onset very poor, but earlier memories relatively intact
Describe Viral encephalitis
- Caused by herpes virus crossing blood-brain barrier
- Sudden onset of acute fever, headache, nausea
- Usually extensive bilateral temporal lobe damage
Describe amnesia in viral encephalitis
- Particularly severe
- Similar to Korsakoff’s, but better insight, and flatter temporal gradient
- Often deficits of spatial and semantic memory
Describe amnesia due to dementia
- Progressive neural disease
- General degeneration of the brain; atrophy (wasting away) due to growth of neural plaques and tangles
- Pattern of impairment involves ‘information-processing’ deficits superimposed upon an amnesic syndrome
Describe Transient Global Amnesia
- Sudden onset of anterograde amnesia
- No loss of personal identity
- Anxious, agitated
- Resolves within 12 hours
- Fairly rare
- Mostly over 50s male
What are the 4 theories of anterograde amnesia?
- Faulty encoding
- Accelerated forgetting
- Faulty retrieval
- Faulty encoding/storage of contextual information
Describe the Faulty encoding theory of anterograde amnesia
Cermak (1979): amnesic deficit due to lack of deep encoding
However, other studies have found similar levels of processing effect in amnesics and non-amnesics
Describe the accelerated forgetting theory of anterograde amnesia
- Some studies show that patients with hippocampal lesions forget faster than controls, even after material has been adequately learned
- In other studies, various different types of amnesics forget at the same rate as controls, provided initial learning is adequate
Describe the retrieval deficit theory of anterograde amnesia
- Transient amnesia shows that retrieval deficits can cause amnesia - once amnesia resolves, memories that were unavailable can be retrieved normally
- Recall is usually always impaired
Describe the theory of deficit in encoding/retrieving context of anterograde amnesia
- Contextual information allows us to distinguish between otherwise similar memories
- Huppert & Piercy (1976): Amnesia due to inability to encode and retrieve contextual information
Describe Hupper & Piercy’s (1976) study
2 groups: Amnesic (Korsakoff patients) & Normal controls
- Presented a set of pictures on Day 1 and a set of pictures on Day 2
- Some were presented on both days
- Recognition test after the Day 2 pictures
- Both groups asked to do 2 tasks:
‘Ever seen recognition’ or ‘Day 2 recognition’
Describe the temporal gradient in retrograde amnesia
Recent memories are more likely to be lost (the opposite of normal forgetting)
Describe consolidation theory of retrograde amnesia
That the older a memory, the longer amount of time the memory has to be consolidated and thus we remember them
Describe standard consolidation theory
- Episodic memories are initially encoded and stored in hippocampus, and retrieving these memories requires reactivating the hippocampus
- Over time, the hippocampal memory trace becomes less important, and the cortex can retrieve the memory without the hippocampus
What are the two types of psychogenic amnesia?
Fugue states and dissociative amnesia
Describe fugue states
- Sufferer typically found wandering, often a long way from home
- Triggers include: severe stress, depressed mood, history of transient organic
- Last a few hours or days
- After recovery, memories from the state are lost
- Very rare
Describe dissociative type
- Refers to loss of memory for specific events due to trauma
- E.g., 25-45% of homicide suspects claim amnesia
