lecture 2 - memory - consolidation Flashcards
how is declarative memory ‘captured’ by the brain
-we known from research that the hippocampus is responsiblefor taking in and consilidating infromation.
The inability to form new memories is caused by damage to the hippocampus and other medial temporal lobe (MTL) structures (“extended hippocampal system”
Henry Molaison (patient HM)
-what did he have
-what surgery was performed on him
-Anterograde amnesia (and retrograde amnesia) resulting from
surgical MTL removal to alleviate seizures in 1953
-the surgery cut parts of his medial temporal lobe
what was the effect of patient HM’s surgery
-it did stop his seizures
-but it caused him inability to form new memories (anterograde amnesia) (and retrograde)
-cannot retain info he processed seconds earlier (would be hard to conversate )
M 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) (but he could speak what he knew how to speak before)
- 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
Hm’s memory , procedural / decalrative
-what does this show
HM’s procedural memories were not effected , only his declarative memories were
DISSOCIATION betwee declarative and procedural memory
Clive Wearing
-what did he have and what was it caused by
Severe anterograde amnesia (as well as retrograde amnesia) due to
damage to multiple subcortical structures caused by encephalitis.
what effect did clive’s amnesia have on him
“His amnesia was so dense that he could remember nothing from more than a few minutes before, a state that he attributed to having just recovered consciousness. Left to his own devices, he would often be found writing down a time, for example 3:10, and the note “I have just recovered consciousness” only to cross out the 3:10 and add 3:15 and then 3:20, etc. If his wife left the room for a few minutes, when she returned he would greet her with great joy, declaring that he had not seen her for months and asking how long he had been unconscious.
- BUT clive has spared musical abilities and can learn new music pieces
what part of brain is important for the aquisition of declaritive memories
- what happens when this part is damaged
The hippocampus is critical for the acquisition of declarative memories
The hippocampus is critical for the acquisition of declarative memories
evidence that hippocampus / medial temporal lobe is critical for aquisition of declarative memories
evidence
-can check normal healthy MTL and see whether their performance during encoding will depend on activity in hippocampus
study on participants where participants learn a list of words, and are in an fmri scanner whilst they do this
normal controls: activation in MTL structures during study predicts whether information will be later
recalled or no
-more activity in medial TL for words that were later remembered than the words forgotton
what does the hippocampus do to aquire declarative memories ,
he 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
why is there two stages to learning
-complementary learning systems model
-McClelland et al. 1995
-solution to this
- 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) (so your not just replacing old memories)
→ less vulnerable memories
knowledge is ______ / _______ information
Remember: knowledge is structured/organized information!
Consolidation = organization (Stickgold & Walker, 2005)
LTM : hippocampus to neocortex
another analogy to understand why there is two stages
O’Reilly and Norman (2002):
to meet two incompatible goals
-you need to have two stages to combine two incompatible goals
-eg look at table
what is consolidation
what are the two types
Consolidation is a slow neocortical learning process that “stabilises” or “fixes” memories in LTM
across hours/days (Wixted, 2004; Dudai, 2004)
1) synaptic consolidation
2) systematic consilidation
synaptic consilidation
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)
systemic consilidation
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).
explain the temporal gradient in retrograde amnesia for memories
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
experiment that shows sleep aids memory
-what does the results tell us
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.”
how does sleep aid memory?
Ellonbogen et al 2006
what are the few hypotheses
- “No benefit” hypothesis [we can rule this one out!]
- “Passive protection” hypothesis: sleep protects against interference (e.g., Jenkins & Dallenbach, 1924)
- “Permissive consolidation” hypothesis: sleep reduces interference, which creates the necessary
conditions for consolidation - “Active consolidation” hypothesis: sleep is directly involved in consolidation
how does sleep aid memory
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
procedural memory and sleep
experiment
Compare performance after x hours of being asleep and x hours of being awake (they did a tapping task)
-→ overnight improvement, and further improvement over subsequent nights (naps help as well; Nishida & Walker, 2007)
→ in contrast, sleep deprivation reduces improvement by 75%
declaritive memory
how do we know sleeep activley protects memories from interference :(Ellenbogen et al., 2006
-study
4 groups
- you learn a-b word pairs, at 9am and then come back at 9pm and get a test
-in test you get given the first word, and then ask you to recall the pair word (word that had been learnt in combination with the first)
-compare this to a group that came in at 9pm and got a full night sleep and come back at 9am and do the test
-the group that was awake between learning and test was able to recall fewer words than the group that got a full night sleep
they also did the exact same test again, but before particpants get a test (whether it be 9am or 9pm) they get given new words to learn (called AC word pairs) (A word is same but pair is different) (interference)
-found the same effect
again another group
-waited 24 hours in between study and test
-9am group came back 9am next day, still went about their day AND slept and performed very well
This group had as many hours of wakefulness as Wake-I, so they could have forgotten as much as Wake-I.
Instead, they perform as Sleep-I.
test case : language
Dumay and Gaskell (2007): learning of new words
test case
preventing consolidation
