week 5 - long term memory Flashcards
Long-term memory:
Holds potentially unlimited amounts of information for potentially unlimited amounts of time
The centrality of long-term memory in everyday life
Sense of continuity between past, present and future
- mental time travel
- autonoetic
consciousness
(Tulving)
Memory forms much of who we are
We need memory to
survive
Modal Model - problem
How short is short, and how long is long?
Confusion in the public and media
long term memory - declarative memory
split into :
1. episodic
Memory for specific episodes and
details.
- Memory for contextually bound specific events.
E.g. your last birthday party
- Semantic
Memory for facts and meaning of things.
e.g. My birthday is on…
long term memory -Non-declarative
implicit memory
- Learning through
prior exposure, but
without consciously
remembering.
e.g. priming
conditioning
Procedural memory
- Memory for skills, including motor skills.
e.g. learning to ride the bike, play the piano etc…
What is amnesia?
The profound loss of long-term memory in the presence of well-preserved cognitive abilities (IQ, language, short-term and working memory).
inability to remember important events from the distant past (e.g. wedding)
inability to remember everyday events from the recent past (e.g. breakfast this morning)
inability to recall what has happened during the day
lack of continuity between past and future
disruptive to everyday functioning
independent living is often not possible at all
What amnesia is not
Forgetfulness
Mild memory problem
Problem remembering names
Causes of amnesia
Physical damage – closed head injury / head trauma
Inflammation of the brain – Encephalitis
Brain tumour and treatment (radiotherapy)
Ischemia – inadequate blood supply
Anoxia – loss of oxygen
Nutritional deficiency (low thiamine) – Korsakoff syndrome
Neurodegenerative disease (e.g. Alzheimer’s disease)
What does amnesia affect?
Affects hippocampus which is central in long term memory.
Patient HM - surgery for epilepsy
Loss of recent memory after bilateral
hippocampal lesions
HM post-surgery observations
He “forgets the events of his daily life as fast as they occur” (Scoville and Milner, 1957)
watching same TV program as new
never recognised B Milner, Suzanne Corkin „vaguely familiar”
surgery - disadvantages
profound anterograde amnesia = no specific event memories since the date of his surgery
No ability to learn?
temporally-graded retrograde memory loss
surgery - benefits / what wasn’t affected
The seisures were reduced -
normal short-term memory span
above average IQ
carries out conversation fairly normally
retained ability to learn motor skills
retained implicit learning
vague familiarity with major news events
(assassination of president Kennedy)
STM vs. LTM
patients with amnesia have largely retained STM abilities:
digit span / verbal span / normal recency effect
HM (temporal lobectomy – Scoville and Milner)
EP (herpes encephalitis – Squire)
KC (traumatic brain injury – Tulving)
Korsakoff patients
earlier stages of Alzheimer’s disease
= classic amnesic syndrome is a disorder of LTM
Double dissociation?
patients with impaired STM but intact LTM
e.g. KF (motorcycle accident – Warrington and Shallice, 1969)
- digit span of 1 or 2
- primacy effect
- recency effect
not amnesic!
LTM and STM
are functionally independent
Anterograde vs. Retrograde Amnesia
Anterograde - Inability to form new memories /
learn new information
(i.e. after the brain injury)
Retrograde - Inability to retrieve memories from the past
(i.e. prior to brain injury)
Procedural memory
retrograde aspect - premorbid motor skills are not forgotten
anterograde aspect - it is possible to learn new motor skills in amnesia
but without remembering the
learning episode itself
Implicit learning
Amnesic patients will complete words with gaps with words they have been shown, there is no difference between healthy and amnesic patients.
There is a difference where amnesic patients do worse when completing the words when telling them that the words they have been shown previously would be helpful as their long term memory is damaged.
Implicit learning is in tact as long as you don’t draw attention to it.
in amnesic patients…
short term memory in tact
long term memory affected, but not non-declarative (implicit and procedural)
Declarative and non-declarative
The evidence for distinct declarative and non-declarative systems is compelling
But, there is no clear evidence for double dissociation (i.e. where non-declarative is impaired, and declarative is retained)
Functional independence of the two is questionable
semantic memory
retrograde - The ability to remember facts and information that were established prior to the brain injury
anterograde - The ability to form new semantic memories after the onset of amnesia is controversial
Episodic memory
retrograde - Most amnesics suffer from some degree of retrograde episodic/event memory loss
But there is high variability in length ranging from a few years to the entire life prior to brain injury
Tends to be temporally graded
HM - what memories were lost?
Childhood memories are still remembered
Memories 5-10 years prior to lesion lost
e.g. forgot death of favourite uncle in 1950
Ribots law - 1982
Older (remote) memories are more durable than those acquired more recently
= recent memories are more likely to be lost in amnesia (and in AD)
Episodic memory - anterograde
Inability to form new episodic memories is the key deficit in amnesia
Episodic memory:
Ability to encode and retrieve personally experienced events in rich contextual detail. (where / when / who / what)
Amnesia: a deficit of recollection?
Two mechanisms of recognition memory:
Recollection: on the basis of retrieving specific contextual details
Familiarity: on the basis of the perceived strength of the memory trace, but without specific contextual details
Evidence
Recollection is selectively impaired or more impaired relative to familiarity in amnesia (Bowles et al., 2010; Skinner and Fernandes, 2007)
A double dissociation between Familiarity and Recollection was also suggested on the basis of patient data – damage limited to the perirhinal cortex leads to a selective deficit in Familiarity only (Bowles et al, 2007, 2011).
Brain mechanisms of recollection and familiarity
Hippocampus plays an important role in binding together contextual details of an event
Is it just the hippocampus?
Similar memory deficits following frontal lesions
Frontal lobes play an important role in conscious control and monitoring of memories during retrieval
Temporal (hippocampal) and frontal impairments very often co-exist (e.g. in Korsakoff Syndrome and Alzheimer’s disease)
Extent of brain damage affects the severity of the memory disorder
various patterns of memory disorders
summary
Bilateral hippocampal damage very reliably causes amnesia
Severity of amnesia depends on the location of the lesion and the extent of damage
Additional frontal lesions exacerbate amnesia
