19 - Episodic Memory I

Question 1

Describe HMs memory deficit

Answer 1

• Spared short-term memory (e.g. repeating a digit sequence)
• Profound anterograde amnesia = inability to learn new information
• Limited retrograde amnesia = inability to remember memories acquired prior to surgery
• Memories for personally experienced events impaired
• Semantic memory (e.g. facts, general knowledge) spared
• Procedural (skill) memory spared
• Priming (a form of implicit memory) spared

Question 2

Where were HM’s lesions and what did this show us about where memory is encoded?

Answer 2

• Had bilateral medial temporal lobectomy
• Medial temporal lobe crucial for acquiring new long-term memories and plays a time-limited role in their storage or retrieval

But not all memory dependent on MTL

Question 3

What is episodic memory?

Answer 3

contains contextual information about where and when some events (what) took place.

Question 4

What is the perhinhal cortex (PRC) important for in memory and what do lesions to this area cause?

Answer 4

Familiarity-based item recognition
- Doesn’t care about context, just the item
Learning associations about and between objects
Object perception

• Lesions lead to impairments in recognising objects, words, faces

Question 5

Where does the PRC mainly project to?

Answer 5

Anterior parts of the hippocampus

Question 6

How does activating the PRC during learning affect later familiarity ratings?

Answer 6

They correlate.

Increased activations = increased later ratings of familiarity

Question 7

What is the parahippocampal cortex important for in terms of memory?

Answer 7

Recollection of context information
Autobiographical memory
Spatial memory and navigation
Scene perception

Similar activation pattern to the hippocampus during recollection

Question 8

Where does the PHC project to primarily?

Answer 8

Posterior parts of the hippocampus

Question 9

How does the PHC respond during learning and retrieval?

Answer 9

High activations during learning and retrieval when context is successfully remembered

Question 10

What is standard consolidation theory?

Answer 10

Information initially represented in different parts of neocortex is bound together into a memory trace by the MTL

There is a short period of cohesion or synaptic consolidation lasting between seconds and minutes.
This is followed by a prolonged period (years) of long-term (or system) consolidation

The MTL is initially necessary for retrieval of these memory traces, but the memory trace is eventually fully consolidated in the neocortex and becomes independent of the MTL.

There is a temporal gradient in retrograde memory
- more distant past memories better preserved

Question 11

What are some challenges to the standard consolidation theory?

Answer 11

Some patients (including HM in retrospect) do not show a clear temporal gradient in retrograde memory.

• Retrograde amnesia can be very extensive (decades)
• Even when old memories are retained, careful testing shows that they are more schematic and lacking in rich detail.

Dissociations in temporal gradients for different types of memory

• Personally experienced episodic memories (autobiographical memory) often impaired for all of the patients past.
• Semantic memories more likely to show a temporal gradient, with better recall of older memories.

Question 12

What does KC’s case demonstrate about episodic memory?

Answer 12

Severely impaired episodic memory for personally experiencing events (autobiographical memory)
- Covers whole life

Temporal gradient for semantic memories pertaining to general semantic facts, public events, famous people
- Only the most recent ~5 years prior to injury