Amnesia

Amnesia

1. Types of amnesia

   • Memory disorder with preserved intellect and language

2. Causes

   • Alzheimer's disease
     • Most common cause > not a pure form
   • Korsakoff syndrome
     • Chronic alcoholism > pure form
   • Herpes simplex encephalitis
     • Very rare virus in the brain (Clive Wearing)
   • Temporal lobe surgery
     • H.M.
       • Epileptic seizures at 10 - surgery at 27
       • Removal of medial temporal lobes and parts of hippocampi
       • No more seizures but became amnesic
       • Severe anterograde deficit and retrograde deficit extends back to age 16 (11yrs before surgery)

3. What is preserved?

   • STM
     • Digit span
   • Procedural memory
     • Mirror drawing task
   • Implicit memory
     • A person's behavior is influenced by previous experience
       • Handshake
       • Can recall words based on images that comes to mind

4. Episodic memory

   • Anterograde amnesia and recollection (free-recall tasks) and familiarity (recognition tasks)
     • Jon
       • Early born (anoxia) > brain structure abnormalities
       • Jon has deficits in recall tasks
       • Uses remember/know categories as often as controls > can't explain the basis of R decisions
       • Remembers visually
       • Deficits in recollection
     • Hypoxic (lack of oxygen to the brain) patients
       • Yonelinas et al. (2002)
         • Deficits in regognition - alike controls in recall
     • Dual-process model of memory (Aggleton & Brown, 1999)
       • There are hippocampal amnesics who have deficits in recall and recognition
   • Rertograde amnesia and temporal gradient
     • Need to test items learned prior to the onset of amnesia
     • Koppelman et al. (1990) developed the Autobiographical Memory Interview (AMI). Ask participants to remember specific information from a range of time periods e.g. the name of their first school. Then recollect a specific personal event from the period
     • Temporal retrograde amnesia gradient
       • For those with retrograde amnesia memories from earlier in life are easier to recall than those later on (Ribot’s law).
       • Butters & Cermak (1986) report the case of P.Z.
     • Explanations for RA
       • Standard consolidation models e.g. Alvarez & Squire (1994)
         • Assume information is consolidated by transferring it from one brain region to another
           • Accounts for Ribot’s law
       • Multiple Trace Hypothesis e.g. Nadel & Moscovitch (1997;1998)
         • The hippocampus is not only important in encoding but also in long-term retrieval
         • Long-term consolidation results in the creation of redundant traces in the hippocampus, instead of the neocortex
         • Predicts that complete hippocampal damage will result in complete RA

5. Semantic memory

   • H.M. tested on ability to retrieve lexical knowledge (Kensinger et al., 2001). Picture naming, spelling, ability to generate irregular word forms (e.g. Every day I dig a hole. Yesterday I ____ a hole). Performed within 1 SD of matched controls.
     • However this knowledge acquired very early in life and generally early childhood memories are found to be well preserved in amnesic patients (Ribot’s law).
   • The amount of damage to MTL corresponds to the magnitude of deficits in acquiring new semantic info (Verfaellie et al., 2000).
   • A number of early onset hypoxic patients show relatively preserved acquisition of semantic knowledge but profound episodic memory deficits e.g. Jon, Vargha-Khadem et al., 1997.

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