COGS101 Lecture Notes - Lecture 7: Neurodegeneration, Traumatic Brain Injury, Temporal Lobe Epilepsy
2 Jun 2018
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Amnesia – Week 7
➢ Amnesia – a loss/failure to form a memory
➢ Retrograde amnesia – a loss backwards in time – memories you had before are
reverted, often happens with psychological trauma, brain injuries etc. (rare)
➢ Most common amnesia – anterograde amnesia → working forwards in time,
the failure to lay down new memories – the person is effectively living in the
present tense, can still remember their past
What is Amnesia?
• Two kinds of memory failure
o Loss of existing memories:
▪ Retrograde amnesia → retro – signifying backwards in time,
forgetting things from earlier parts of your life
o Failure to form new memories:
▪ Anterograde amnesia → antero – signifying loss of memory for
events occurring in front, or (just) earlier, forgetting what has
just happened
Different kinds of Amnesia:
• Retrograde amnesia
o Prevalent in Hollywood
o Rare elsewhere
▪ Dissociative amnesia
▪ Psychogenic amnesia
▪ Functional amnesia
• Following emotional trauma → past psychiatric history
• Some precipitating ‘event’
• Neurological cause unlikely?
o Retrograde amnesia can be neurological
o Focal retrograde amnesia
▪ Stroke
• Case JG – 33 year old man with thalamic strokes, lost
more personal memories throughout life
▪ Epilepsy
• Case JB – 21 year old woman who did not know she
had been to Italy, tests showed she was having seizures,
patchy retrograde amnesia
o Everyone has some difficulty remembering the past – normally, remote
memories are affected most
o With clinical retrograde amnesia, recent memories are usually affected
more than remote memories
▪ Ribot’s Law (last in, first to go)
▪ Shrinking of extent with recovery
o Usually autobiographical
▪ Cannot remember events and people from one’s own
experienced past
o But also can affect knowledge about general events and people –
famous faces test
o Usually doesn’t affect personal knowledge
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▪ Identity is intact
o Affects declarative memory
▪ Previously learned information one can reflect upon, BUT in
general retrograde amnesia is hard to test
o Doesn’t affect procedural memory
▪ Can still perform old skills
• Anterograde amnesia
o Much more common – ‘short term memory loss’, rapid forgetting
o Everyone experiences some degree of forgetting
▪ Normally often remindable
▪ Some kind of memory trace exists
o In clinical cases, memories are formed in the immediate term, but they
are not enduring
▪ Failure to consolidate new learning
▪ Or a failure to retrieve newly learned information
▪ Forgetting can occur after a few minutes, or over hours
▪ In extreme cases, the person effectively lives in the ‘present
tense’ continually
• Henry Molaison (HM)
• Clive Wearing
o Affects declarative learning
▪ Learning of new information one can reflect upon
▪ In general, anterograde amnesia is easy to test
o Procedural learning is again usually in tact
▪ Can learn new skills
o Often accompanied by some degree of retrograde amnesia
▪ But can only really say this when a time of brain injury can be
established (stroke, head injury)
What causes Amnesia?
• Loss of memory part of dimensia – result of Alzeihmers disease (most
common)
• Other accidents like head injury/trauma e.g. stroke
• Epilepsy – temporal lobe to the brain can cause amnesia (bitter kind of
forgetfulness) – sometimes can only affect one side of the brain
Explaining Amnesia – Causes and Models:
• Two kinds of amnesia
o Retrieval failure – enduring memories of experiences are created, but
access to them is impaired
• Tests requiring recall are failed
• Tests requiring recognition may reveal the memory
▪ Frontal lobe dysfunction may be responsible
o Usually not primarily a problem with memory
▪ Often other deficits → attention, planning, general retrieval
difficulty (names etc.)
• Causes of retrieval failure:
o Traumatic brain injury – frontal lobes, diffuse axonal damage
o Depression – neurochemical imbalance in fronto-striatal circuitry
find more resources at oneclass.com
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