1. Medio temporal lobe atrophy Lateral Temporal lobe atrophy
Alzheimer’s disease vs. Semantic Dementia
(episodic deficit vs. semantic deficit)
Alzheimer’s
Medio temporal lobe atrophy
Semantic Dementia
Lateral Temporal lobe atrophy
Graham et al. 2000

2. semantic task Task: Name this object Correct answer: ‘phone’.
Alzheimer’s disease
Semantic
dementia
Task: Name this object
Correct answer: ‘phone’.

3. 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’

4. 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’

5. Episodic Memory: Results
Alzheimer’s disease
Semantic
dementia
Perceptually Identical
Perceptually
different
Semantic Dementia patients
OK if perceptually identical items
- Spared Episodic memory
Impaired if perceptually different items
- Impaired semantic memory
(doesn’t know that the two different looking
phones belong to the same category ‘phone’)
Alzheimer’s patients
Impaired, even if perceptually identical
Impaired Episodic memory.

6. 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.

7. Does the hippocampus have a time-limited role in memory consolidation?
Temporal Gradient:
In amnesic patients (hippocampal lesion, such as HM, Alzheimer’s 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

8. Spare slides

9. From Patterson, 2007, NatNeuroRev

10. From Patterson, 2007, NatNeuroRev

11. From Patterson, 2007, NatNeuroRev