memory Flashcards
how can you describe human memory?
the storage and retrieval of information between sensory, short-term and long-term
what do pre-frontal cortex lesions impair in macaques?
performance on tests of spatial working memory
(delayed alternation and delayed response tasks)
cannot select correct response on basis of info held in working memory
[Goldman 1984]
what and where is the prefrontal cortex
cerebral cortex covering the front part of the frontal lobe
orchestrates thoughts and actions in accordance with internal goals
what are the properties of dorsolateral PFC neurons?
have activity that is specific to particular locations + sustained across delays
representations are maintained in an active state even during delays
Funahashi 1991
what do PFC neurons have access to and how do they encode it?
information relevant to the current task
encode the spatial position of a stimulus or the identity of it depending on what is relevant in each task phase [Rao]
what does BOLD stand for?
blood oxygenation level dependent imaging
when does human PFC BOLD activity increase in the WCST?
at the point subjects get feedback about which dimension of a multiple dimension stimulus should be attended to in the Wisconsin Card Sorting Task [Konishi]
what is the wisconsin card sorting task? what is the point of it?
subjects are asked to match a stimulus card to 1 of 4 reference cards placed on the table with varying dimensions
dimensions = number, colour, shape
they are given feedback when matches are right or wrong
repeat with 64 or 128 cards
see if they get better at identifying what the key characteristic the cards should be matched on is
[to measure frontal lobe dysfunction]
why do patients with PFC lesions find the WCST difficult?
they struggle to use the feedback and keep it in their working memory to change the information they consider relevant for sorting the card
if told the match is wrong, on the next case, will not learn from that ?
what is the dorsolateral PFC critical for?
maintaining temporal organisation of memory
monitoring the contents of working memory
what is the recency effect?
tendency to remember the information most recently presented, best
what do prefrontal lesions impair?
recency judgements for information in working memory
gets worse as number of items to be remembered increases
don’t affect recognition judgements [Petrides]
what is a recency judgement?
a list of words presented sequentially
then subjects presented with 2 of the words at the same time and asked which was studied more recently
PFC activated
what do temporal lobe cortex lesions impair?
performance on recency judgement tests as length of delays increase [Petrides]
what were the findings of Sakai and Passingham (2002) about the PFC?
dorsolateral PFC activity increases during spatial working memory (also in posterior parietal cortex + frontal eye field)
if activity in dorsolateral PFC decreases then errors are more likely to be made
activity in PPC and FEF tightly correlated when performance is correct
activity in D PFC is high, correlation between PPC and FEF is high
what might be the functional specialisation of the PFC?
dorsolateral = spatial working memory
ventrolateral = verbal working memory
what is the role of hippocampus in memory?
implicated in spatial memory
what is the hippocampus a central component of?
the medial temporal lobe
what was the lesion of patient HM?
bilateral surgical lesion of hippocampus and adjacent cortex
(for epilepsy treatment)
what was the result of the lesions of patient HM?
severe anterograde amnesia
cannot form long term memories
[Scoville and Milner 1957]
what were the findings from HM , and why were they important?
- first demonstration of localisation of cognitive function
- his short term and working memory were normal (rel. unimpaired in tests of verbal memory span) : DISTINCTION BETWEEN LT AND ST MEMORY
- retained the ability to learn motor skills tasks: mirror drawing + rotary pursuit : DISTINCTION BETWEEN DECLARATIVE AND PROCEDURAL MEMORY
what did Warrington and Weiskrantz show about amnesiacs?
they had unconscious memories for stimuli in priming tests shown to them once
amnesiacs improved at identifying degraded pictures and completing stems of words to which they had been exposed
what can explain amnesiacs’ unconscious memories after priming?
the memories spared after hippocampal regions reflect plasticity in certain non-integrated circuits e.g. perceptual/cognitive/motor
fragmentary memories cannot give rise to conscious percepts
why does amnesia occur?
damage to hippocampus and associated limbic and cortical areas
what is the medial temporal lobe?
includes the hippocampus, amygdala and parahippocampal regions
is crucial for episodic and spatial memory
what is episodic memory?
a memory centred around an event
e.g. you had an enjoyable trip to Paris that you remember
you remember that classroom was painted blue when you learnt that Paris was the capital of France
what is semantic memory?
a memory of facts
e.g. the independent knowledge that Paris is the capital of France
a memory abstracted from the specific experience of being in Paris
what can damage the medial temporal cortex?
herpes encephalitis virus
alzheimer’s
what evidence is there that different MTL regions are critical for different aspects of memory?
Maguire on taxi drivers: rhinal cortex for object related memory vs hippocampus for spatial memory
Lee : semantic dementia patients have more damage to temporal lobe outside hippocampus and are more impaired on face discrimination. alzheimer’s patients have more damage to hippocampus itself and are more impaired on scene discrimination
what is the distinction in areas of the brain between remembering and knowing? what is the experiment?
remembering = hippocampus
knowing = rhinal cortex
Ranganath 2004: see words in red or green + make judgements about their size/animacy. fMRI taken simultaneously
then subjects indicate confidence whether have seen the words before (rhinal cortex) and attempt to identify their source (hippocampus)
what are the other regions besides the MTL critical for memory?
connections of the hippocampus : mammillary bodies, dorsomedial thalamus
what is Korsakoff’s syndrome?
thiamine (vitamin B1) deficiency e.g. in alcoholism
damages limbic structures interconnected with the hippocampus (MBs, DT), causing severe amnesia
what do the excitatory connections between different hippocampal subregions show?
experience-dependent plasticity that may be related to memory
what does a burst of activity in a local pathway in the hippocampus cause?
instant and long-lasting enhancement/potentiation of the excitability in the pathway
(LONG-TERM POTENTIATION)
[Bliss and Lomo 1973]
What is Hebb’s Law? (1949)
“When an axon of cell A is near enough to excite cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased”
is LTP associative?
yes
specific to synapses between presyn and postsyn neurons that were activated at the same time
oversimplify classical conditioning:
involves the changes of reflex actions based upon associations between stimuli
now explain classical conditioning properly:
neutral conditioning stimulus (bell) paired with unconditioned stimulus (food) that triggers reflexive unconditioned response (salivation)
with training, CS triggers learned conditioned response (salivation)
what is operant conditioning?
the frequency of a naturally occurring voluntary behavioural response is changed by association with reward
what are the associative changes seen in LTP reminiscent of?
associative learning
- classic and operant conditioning
- Hebb’s Law
what is the modal model of memory?
as information enters the brain it is encoded and stored in memory systems: sensory register, short-term memory, long-term memory
[Atkinson-Shiffrin]
what did the modal model influence?
Levels of Processing Model : Craik and Lockhart 1972
what does the modal model suggest happens to unattended information?
it is filtered out and lost from the sensory register within seconds
“cocktail party effect”
what ordinarily happens in short-term memory?
info stored for up to 30 secs without effort being made to remember it, then it is also lost
if you rehearse/encode it, info can be held for longer and transferred to long-term memory
what type of encoding is favoured for short-term memory by the modal model?
auditory
visual perception of a phone number but auditory encoding of it by repetition
how else can you improve short term memory than auditory repetition?
chunking:
e.g. 82-64-97 not 8-2-6-4-9-7
what does long term memory hold?
all the info we know but are not consciously aware of at any given moment
