Transcript Disorders of Memory (NM)

What you need to know
• What you need to know
– Two types of memory disorder (amnesia and
Alzheimer's)
– A description of these two disorders
– Explanations of these two disorders
– Research into these explanations
Amnesia
• Definition: A partial or total loss of memory,
either temporarily or permanently
– Retrograde amnesia: the total or partial loss of
memory for past events
– Anterograde amnesia: the inability to form new
long term memories.
• HM (info on green box pg 95)
• Clive Wearing
Explanations of amnesia
• Explanations of
amnesia - 1
– Loss of explicit memory
• Explanations of
amnesia – 2
– Inability to consolidate
new memories
Explanations of Amnesia - 1
• Explicit vs implicit memory
– Explicit memory: information deliberately and
consciously recalled.
– Implicit memory: something known without
conscious recollection
• Learning a list of words deliberately so that
they can be recalled:
• Being asked to recall a list of all the pubs
you have been to:
Explanations of Amnesia - 1
• Schacter (1987)
– One possible explanation of amnesia is that it is
caused by an impairment in explicit memory. (AO1)
– When tested, amnesiacs perform poorly on tests of
explicit memory but their performance on implicit
memory is almost normal.
• Warrington & Weiskrantz (1968) (AO2)
– Tested HM (anterograde amnesia) using the Gollin
test (see pg 109)
– Was able to recognise partial images, although he
had no memory of doing the test
Explanations of Amnesia - 1
• Stickgold (2000)
– People with normal memory can learn Tetris in a
few hours, and describe it
– People with amnesia can improve (although
slower) showing implicit memory, but have no
explicit memory of having done so.
Explanations of Amnesia - 1
• Procedural vs declarative memory (LTM)
– Procedural memory: how to “do” something. Motor
skills. The skill of swimming for example.
– Declarative: fact based memory. Knowing the fact
that you can swim for example.
• If amnesiacs are better at implicit rather than
explicit memory, how do you think they would
perform on procedural vs declarative tasks?
Explanations of Amnesia - 1
• Milner (1962)
– Taught HM how to draw using a mirror
– After practice, HM had learned the
skill (procedural) of drawing with a
mirror, although he had no memory of
being able to do it (declarative)
• Stickgold (2000)
– It could be argued that participants in
Stickgold’s study were able to develop
a procedural memory for Tetris, but
not a declarative memory
Explanations of Amnesia – 1
• All of the previous suggests that amnesia may
be caused by an impairment in
explicit/declarative memory.
• This explanation is descriptive rather than
explanatory.
• Ryan et al (2000)
– Relational memory binding
– Amnesiacs lack the function which makes a link
between implicit and explicit memory (Still
descriptive?)
Explanations of Amnesia - 2
• An alternative theory is that Amnesia is the
result of a problem with the consolidation of
long term memory
• Issac and Mayes (1999)
– Tested anterograde amnesiacs by learning word
lists. Amnesiacs performed normally on cued
recall and recognition, but poorer than controls on
free recall of semantically similar words.
– Suggests that there is an impairment in
consolidation of long-term memory, not with
retrieval.
Explanations of Amnesia - 2
• Temporal gradient
– In people with retrograde amnesia recall is poorer
the closer the memory is to the onset of amnesia
Recall of memory
Onset of amnesia
Time
Explanations of Amnesia - 2
• This temporal gradient indicates that
memories need to be consolidated and
integrated into LTM, otherwise they are lost.
• Therefore, amnesia is caused by a disruption
of this consolidation.
Explanations of Amnesia - 2
• What causes problems with consolidation?
– Problems with consolidation may be due to
damage to the hippocampus
• HM
• His amnesia was caused by surgery
that removed his hippocampus,
amygdala and parts of the temporal
lobes
• Clive Wearing
• Had a virus which attacked his
brain, damaging the hippocampus
amongst other parts
Explanations of Amnesia - 2
• Gabrieli (1998)
– Although many amnesiacs have both retrograde
and anterograde amnesia, damage to a specific
part of the hippocampus (CA1) causes
anterograde amnesia alone.
• Reed and Squire (1998)
– Used MRI scans on retrograde amnesiacs. All had
damage to the hippocampus, but those with the
worst symptoms also had damage to the temporal
lobe.
• Think HM
Explanations of Amnesia - 2
• Remondes & Scman (2004)
– Rats with damage to the hippocampus could learn
a new maze, but forgot it quickly.
– Suggests that hippocampus in involved in the
consolidation of new memories.
Evaluation of Research
• Issues with using brain damaged patients?
• Issues with using animals?
Alzheimer’s Disease
• A progressive form of dementia that usually
starts in the 40s or 50s.
– Impaired memory
– Impaired thought and speech
– Finally complete helplessness
Auguste Deter, the first person to be
diagnosed by Alois Alzheimer in 1901
Explanations of Alzheimer’s
• Explanation of Alzheimer’s 1
– β-amyloids, plaques and tangles
• Explanation of Alzheimer’s 2
– Genes
Explanation of Alzheimer’s - 1
Normal Individuals
Amyloid precursor
protein (APP)
broken down into
β-amyloid protein 40
Builds up in spaces between
neurons causing plaques
Plaques cause damage to
cerebral cortex, hippocampus
and basal forebrain
Individuals with Alzheimers
Amyloid precursor
protein (APP)
broken down into
β-amyloid protein 42
(referred to as β-amyloid)
Interferes with
neurotransmitter NDMA
Interferes with changes to
neurons during learning
Explanation of Alzheimer’s - 1
• Plaques cause problems in communications
between neurons
• Selkoe (2000)
– Plaques start to form before symptoms of
Alzheimer's. Progressive damage causes cerebral
cortex to shrink
– The hippocampus is also affected
• Berntson et al (2002)
– Alzheimer's effects memory is because of damage
to the basal forebrain which is involved with
alertness and attention
Explanation of Alzheimer’s - 1
• The link between the build up of plaque and
Alzheimer’s is weak and hard to explain.
• Murphy & LeVine (2010)
– The presence of β-amyloid protein 42 early in the
disease starts a chain of events that leads to the
illness
– This has yet to be tested
Explanation of Alzheimer’s - 1
• Snyder (2005)
– β-amyloid protein 42 interferes with NDMA, a
neurotransmitter which produces changes in
neurons when we learn
• Cleary et al (2005)
– Injecting rats with β-amyloid disrupts memory
Explanation of Alzheimer’s - 1
• Tangles
– Structure of the cell body disintegrates
– Build up of tau protein
– Distinct form in Alzheimer's
Explanation of Alzheimer’s - 1
• Much of the research into Alzheimer’s comes from
animal studies
• However, every animal investigated is different
– Primates have the same β-amyloid protein as humans, but
do not develop cognitive problems in old age
– Dogs do deposit β-amyloid with age, but do not develop
plaques and tangles
• Generalisability?
Explanation of Alzheimer’s - 2
• Most individuals with Downs Syndrome (DS)
who reach middle age develop early onset
Alzheimer’s: Lott (1982)
– As DS is caused by having an extra copy of gene
21, this led researchers to look for and find genes
associated with Alzheimer's on gene 21
Explanation of Alzheimer’s - 2
• Levy-Lahad eta al (1995)
– Early onset Alzheimer’s gene found on
chromosome 1
• Schellenberg et al (1992)
– Early onset Alzheimer’s gene found on
chromosome 14
• Ertekin-Taner et al (2000)
– Gene for later onset Alzheimer’s found on
chromosome 10
Explanation of Alzheimer’s - 2
• What do the genes do?
– These genes play a role in producing
more β-amyloid, explaining why
these individuals are more prone to
Alzheimer’s
• However: St George-Hislop (2000)
– Half of all Alzheimer’s patients have
no known relative with the disorder
– Suggests the genetic influence is
small.
Explanation of Alzheimer’s - 2
• It seems unlikely that genes are the only
influence on the development of Alzheimer’
• Hendrie (2001)
• The Yoruba people of Nigeria
have the same frequency of
Alzheimer’s related genes,
but a much lower incidence
of the illness
• Other factors such as diet
play a part
Evaluation of Research
• Issues with using animal studies
• Nature vs nurture