Amnesia Flashcards
Patient HM (Henry Molaison)
Had Bilateral removal of the hippocampus to treat epilepsy
What did HM suffer from?
Severe Amnesia
* unable to remember events since operation (anterograde amnesia)
* loss of personal memories up to 11 years prior to surgery (retrograde amnesia)
What aspects of HM’s memory were preserved?
- short-term memory
- knowledge of previously-acquired facts (semantic memory)
- motor skill learning; perceptual learning; non-declarative (non-conscious) memory
but what was wrong with HM’s brain?
visually all anterior hippocampus and surround cortex removed bilaterally, plus amygdala
what happens when there’s damage to the hippocampus?
As the hippocampus is a key part of the network - damage to these associated structures cause amnesia
* there must be bilateral damage affecting these structures in both hemispheres
most patients have less specific damage than HM. This causes a broader range of deficits beyond episodic memory
what is the hippocampus linked to?
episodic memory (as decovered from specific brain removal from HM) -> image to hippocampus leads to amnesia but more / less specific damage may lead to broader deficits
what does anterior temporal damage lead to?
problems with semantic memory and language
what does prefrontal damage lead to?
problems with retrieval and personality
what is herpes simplex encephalitis?
Herpes simplex virus spreads from the face along cranial or olfactory nerves to the brain
who was affected by HSE?
Clive Wearing and Patient EP (Insausti et al., 2013) are examples of relatively pure cases of amnesia following HSE
what does HSE usually affect?
typically focussed in medial and anterior areas (including hippocampus), there is often also damage to anterior temporal and inferior medial frontal cortex.
what are the first symptoms of HSE?
fever, confusion, epileptic seizures, anterograde and retrograde amnesia
what are later symptoms of HSE?
- semantic deficits (category-specific - trouble with knowledge and name retrieval for animals and people)
- often wide spread damage and deficits
What is Hypoxic Brain Injury?
Brain cells start to die after 4-6 minutes of oxygen deprivation. The brain is 2% of the body’s weight yet uses 20% of its oxygen
What are the effects of Hypoxic Brain Injury?
individuals who survive an hypoxic episode often have amnesia -> contained to the hippocampus because the brain relies mostly on oxygen here -> quite similar to pure amnesia and only affects episodic memory
- effects of hypoxia are especially severe in the hippocampus as these cells use a lot of oxygen
What did Zola Morgan et al., 1986 find as a result of patient RB?
causes of hypoxic brain injury include heart attack, respiratory failure, carbon monoxide posioning and disruption in brain flow to the brain i.e. following a haemorrhage
what areas does a hypoxic episode effect?
bilateral hippocampus