Alzheimer

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• Alzheimers disease vs. Semantic Dementia
• (episodic deficit vs. semantic deficit)

Graham et al. 2000
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semantic task

• Task Name this object
• Correct answer phone.

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Episodic Memory task perceptually identical

• - See object
• - 30 delay
• Task Which object did you see 30 minutes ago?
• Possible Correct answers
• - I saw a phone
• - I saw this item in the left

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Episodic Memory task perceptually different

• See object
• 30 min delay
• Task Which object type did you see 30 minutes
  ago?
• Correct answer
• - I saw a phone

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Episodic Memory Results

• Semantic Dementia patients
• OK if perceptually identical items
• - Spared Episodic memory
• Impaired if perceptually different items
• - Impaired semantic memory
• (doesnt know that the two different looking
• phones belong to the same category phone)
• Alzheimers patients
• Impaired, even if perceptually identical
• Impaired Episodic memory.

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Summary Dissociation between semantic and
episodic memory

• Results suggest separate systems for
• Encoding episodic memory Mediotemporal lobe
  (hippocampus)
• Storage of semantic memory Lateral-temporal lobe
• Additional support the dissociation
• 4 patients with selective hippocampal damage who
  all show impaired episodic but intact semantic
  memory (Vargha-Khadem, 1997)
• Note all sustained hippocampal damage early in
  life, so does not necessarily generalize to adult
  brain.

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Does the hippocampus have a time-limited role in
memory consolidation?

• Temporal Gradient
• In amnesic patients (hippocampal lesion, such as
  HM, Alzheimers disease), memories from earlier
  in life are easier to remember than more recent
  memories
• Reverse Temporal Gradient
• In semantic dementia patients (lateral temporal
  lobe atrophy), recent memories are easier to
  remember than more distant ones
• Possible interpretation
• Recent memories live in hippocampus, thus are
  spared in semantic dementia
• Distant memories live in neocortex, thus are
  spared in HM
• Caveat
• fMRI data is inconclusive on whether distant
  memories trigger less hippocampus activation than
  recent ones

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Spare slides
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From Patterson, 2007, NatNeuroRev
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From Patterson, 2007, NatNeuroRev
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From Patterson, 2007, NatNeuroRev