lecture 2- consolidation

Question 1

How is declarative memory “captured” by the brain?
The inability to form new memories is caused by damage to the hippocampus and other medial temporal lobe
(MTL) structures (“extended hippocampal system”).

Question 2

patient HM

Answer 2

HM had spared STM/WM, but was unable to form new declarative memories (anterograde amnesia):
* could not remember new information, his doctors’ names
* could not learn new words (e.g., jacuzzi)
* could not continue a conversation if interrupted
* (also some evidence of retrograde amnesia)
HM was able to form new procedural memories:
* motor learning (e.g., mirror-tracing)

Question 3

memory and the brain

Answer 3

The hippocampus is critical for the acquisition of declarative memories
– amnesics: damage results in inability to form new memories
– normal controls: activation in MTL structures during study predicts whether information will be later
recalled or not

Question 4

LMT: hippocampus => neocortex

Answer 4

The hippocampus binds information together quickly to create higher-level representations
(“soft” connections)
* the hippocampus is NOT a long-term storage site:
damage does not harm already formed memories
These representations are then stored/distributed across networks in other cortical areas,
becoming integrated with old information (“hard” connections)
* semantic memory = neocortical associative network
(Martin & Chao, 2001; Patterson et al., 2007)

Question 5

LTM: hippocampus => neocortex

Answer 5

Why two “stages” to learning?
Complementary learning systems model (McClelland et al. 1995):
* new information can interfere and replace old information (“catastrophic interference”)

• solution:
  – fast, initial episodic learning mediated by the hippocampus
  → vulnerable memories
  – slow, long-term storage in neocortex, involving integration with
  existing knowledge (integration reduces interference)
  → less vulnerable memories
  Remember: knowledge is structured/organized information!
  Consolidation = organization (Stickgold & Walker, 2005)

Question 6

consolidation takes time

Answer 6

Consolidation is a slow neocortical learning process that “stabilises” or “fixes” memories in LTM across hours/days (Wixted, 2004; Dudai, 2004)

1. Synaptic consolidation
   Consolidation can be described in terms of changes in synaptic firing in the brain:
   “the process [of consolidation] involves a rapidly formed and relatively long-lasting increase in the
   probability that postsynaptic neurons in the hippocampus will fire in response to neurotransmitters
   released from presynaptic neurons” (Wixted, 2004).
2. Systemic consolidation
   Consolidation can be described as a gradual shift of a memory’s reliance away from the
   hippocampus and to the cortex (accomplished by repeatedly “replaying” a memory’s various
   components until they are interlinked; may take years to complete).

Question 7

consolidation takes time cont

Answer 7

Consolidation is a slow neocortical learning process that “stabilises” or “fixes” memories in LTM
across hours/days (Wixted, 2004; Dudai, 2004)
* temporal gradient in retrograde amnesia: recently formed memories are recalled more poorly than remote
memories, presumably because they didn’t undergo consolidation (e.g., Alvarez & Squire, 1994)
* transfer to neocortex begins during “offline” hours (i.e., during sleep), when you process minimal external
input (Rasch & Born, 2007)

Question 8

Jenkins and Dallenbach (1924)

Answer 8

Participants learned nonsense syllables, were tested at various intervals.
Results: ~twice as many syllables reported after sleep than after being awake.
Conclusion: sleep may “protect” memories from interference

“The results of our study as a whole indicate that forgetting is not so much a matter
of the decay of old impressions and associations as it is a matter of interference,
inhibition, or obliteration of the old by the new.”

Question 9

Ellenbogen et al (2006):

Answer 9

the role of sleep in declarative memory consolidation: passive, permissive, active or none?

1. “No benefit” hypothesis [we can rule this one out!]
2. “Passive protection” hypothesis: sleep protects against interference (e.g., Jenkins & Dallenbach, 1924)
3. “Permissive consolidation” hypothesis: sleep reduces interference, which creates the necessary
   conditions for consolidation
4. “Active consolidation” hypothesis: sleep is directly involved in consolidation

Question 10

sleep aids memory- how?

Answer 10

• particularly for procedural learning
• but also declarative learning (Ellenbogen et al., 2006; Gais & Born, 2004; Marshall & Born, 2007)
• early sleep – primarily slow-wave sleep (SWS), important for the consolidation of hippocampus-dependent declarative
  learning (as well as for procedural learning)
• late sleep – primarily REM sleep, important for procedural learning, no immediate benefit for declarative memories
  (except for emotional declarative memories)
• but no clear dichotomy

Question 11

procedural memory

Answer 11

Procedural memory is a type of long-term memory that enables us to perform tasks and skills without conscious effort

Question 12

declarative memory

Answer 12

a type of long-term memory that involves conscious recollection of particular facts and events:

Question 13

preventing consolidation

Answer 13

“Simulate” amnesia by interfering with the consolidation process:
* Midazolam: impaired recognition of pictures of common objects when tested 24 hours later (Nyhus & Curran, 2012)
* Alcohol: impaired recall of a mock crime compared to sober controls (Van Oorsouw & Merckelbach, 2012)