Download Serial model Amnesia Amnesia HM

Serial model
Neurobiology of
Learning and Memory
Memory terminology based on information
processing models
e.g., Serial Model
Prof. Stephan Anagnostaras
Lecture 3: HM, the medial
temporal lobe, and amnesia
Can test these models in brain damaged subjects
Amnesia
Amnesia
resulting from shock, psychological disturbance,
brain injury, or illness.
Organic caused by shock, brain injury, illness
• hypoxic episode, herpes encephalitis
• epilepsy, brain injury, Alzheimer’s disease
Psychogenic caused by psychological trauma
• dissociative disorders
• psychogenic fugue
• multiple personality disorder
HM
Amnesia can be global or material-specific
Global any kind of information is affected
Material-specific certain kinds of material
(e.g., faces)
Amnesia can be anterograde or retrograde
Anterograde amnesia inability to learn anything new
since the time of the trauma (usually organic)
Retrograde amnesia loss of memory for events prior
to the time of the trauma (psychogenic or organic)
HM’s lesion: bilateral medial temporal lobe removal
Amnesia Partial or total loss of memory, usually
Most famous case reported by Scoville
& Milner (1957)
Scoville did the surgeries for psychosis
but didn’t work, so tried it for epilepsy on
about 30 patients. Patients studied by
Brenda Milner
HM: bilateral medial temporal lobe
lesion for status epilepticus in 1953
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HM = no hippocampus, amygdala, overlying (rhinal) cortex
HM = no hippocampus, amygdala, overlying (rhinal) cortex
normal
hpc
HM = no hpc, no rhinal ctx
HM’s amnesic syndrome
Retrograde vs. anterograde amnesia
normal memory
for remote events
(childhood, etc)
Severe deficit (global anterograde amnesia)
• show word or face, ask later, doesn’t know
• reads newspapers repeatedly
• doesn’t remember own physician
• see on formal tests or everyday life
• word lists
• faces and objects
• recall or recognition
for HM, retrograde amnesia
is approx. 2 yrs
Retrograde and anterograde
amnesia can occur together
or separately (HM has both)
HM also has this
Only mild retrograde amnesia
• loss of memories that are a up to 2-3 years old at the
time of the lesion, but childhood memories in tact
• known as a time-limited or
temporally-graded retrograde amnesia
Medial temporal lobe amnesia:
what’s special?
Remote versus Recent Memory:
HM, Loss of Recent memory
Deficit very specific for Long-Term Memory (LTM)
• not dementia
• IQ normal and unchanged
• perceptual skills excellent
• social skills and personality intact
• Short-Term Memory (STM = 3 min, 7±2 items) good
(e.g., digit span)
• forgetting curve for STM normal
• Memory scale more than 3 std dev from controls!
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Rey-Osterrieth Figure
Rey-Osterrieth Figure
Famous Faces test of explicit memory and retrograde
amnesia
NF = non-famous (control)
Retrograde amnesia often shows a gradient: memory for
older events (1950’s) is better than memory for newer
events (1980’s)
Amnesics worse than controls
Damage to hpc = Memory that was still in hpc “buffer”got lost
before it could be consolidated into permanent memory
elsewhere in the brain
HM could improve on task but didn’t recognize task each
day
Learns some things normally:
• visual motor pursuit
Spared learning
Fig.
14.4
• priming
• mirror drawing task
• normal eyeblink classical conditioning
(e.g., puff of air/tone on eye but not fear)
• but doesn’t ever remember doing task before (source
amnesia)
These tasks do not necessarily share anything in
common.
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Repetition Priming: Testing Implicit
Memory (Graf et al., 1984)
But they still can
HM improved in performance despite not remembering the
test
First the list:
Fig.
14.6
Then complete the word:
ABSENT
INCOME
FILLY
DISCUSS
CHEESE
ELEMENT
ABS__________
INC__________
FIL__________
DIS__________
CHE__________
ELE__________
complete the fragment
Amnesics don’t
with the previously
remember word list well
seen word
• free recall
• cued recall: complete word stem
with specific word from study list
abs____ ??
• word stem completion: complete
word stem with first word that
comes to mind
dis___??
• same cue in cued recall & word-stem
completion but only cued recall requires
conscious access to past
Mirror Reading
Some spatial
memory
Memory impacted by the lesion termed explicit (or
declarative) memory - must be stated verbally and
requires conscious recollection (note: doesn’t work for
animals) -includes semantic (facts, knowledge) and
episodic (events, memory) memory
Not disrupted: implicit memory (procedural or
nondeclarative) - learning is demonstrated through
performance and may not be available to verbal
recollection (e.g., tying your shoelaces)
Note that implicit memory is a junk term that
includes several different forms of memory,
including most forms of classical conditioning
Neuroanatomy
Explicit versus Implicit Memory
• The hippocampus is the critical
structure for explicit memory
Patient RB: damage only to CA1
• Disruption of hippocampal-circuitry can
give a similar deficit (dorsomedial thamalus)
• The greater the disruption to surrounding cortex the
more severe the amnesia
• Anterograde and retrograde amnesia usually
correlated (HM is an exception)
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More selective brain damage can produce explicit memory
problems (amnesia), also
RB’s brain
Korsakoff’s amnesia:
damage to MD thalamus
(diencephalon area of brain)
Pt R.B.:
damage to
CA1 area of hpc
(very selective)
medial diencephalic
amnesia
(Korsakoff’s and Pt N.A.)
Zola-Morgan, Squire, & Amaral, 1986
Herpes encephalitis
Alzheimer’s disease: plaques & tangles in memory areas
Normal
Herpes Simplex
Encephalitis
Other forms of amnesia
Multiple memory systems in the brain
Unilateral hippocampal damage results
in material-specific deficits
left = words, names, etc.
right = faces, objects, etc.
Korsakoff’s psychosis results in similar
amnesia plus confabulation
Frontal lobes STM, working memory,
temporal order, confabulation
Reed & Squire (1998)
•severe and more general memory loss
(explicit + verbal implicit, e.g., priming)
•affects entorhinal ctx (1), then hpc (2), frontal (3),
parietal (3) lobes
Explicit memory
Medial temporal lobe; diencephalon
Implicit memory
Classical conditioning
Facts
(semantic)
Events
(episodic)
Procedural memory:
skills & habits
Skeletal musculature
(basal ganglia)
(cerebellum)
Priming
(neocortex)
Emotional
Responses
(amygdala)
Eyeblink conditioning in
rabbit
Electroconvulsive Therapy (ECT,ECS)
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Classical (Pavlovian) conditioning and memory
HM normal on this? Explicit or Implicit learning?
There are many different forms of classical conditioning
and the responsible brain structure depends on the form
Examples:
a) Pavlovian fear conditioning:
Tone --> Shock
Then: Tone --> freeze
(CS)
(US)
(CS)
(CR)
• Depends on the amygdala
• + the hippocampus with trace procedure
• + the hippocampus if the CS is a context
b) Eyeblink conditioning
Tone --> puff of air to eye
Then: Tone --> eyeblink
(CS)
(US)
(CS)
(CR)
•Depends on cerebellum
• + hippocampus with trace procedure
• Declarative knowledge of task always depends on hippocampus
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