Amnesia, Unlearning, and Forgetting

• HM's brain damage was the result of surgery to alleviate severe temporal lobe epilepsy
• Boswell's and Wearing's brain damage were due to herpes simplex encephalitis
• In all three cases, the damage to the brain occurred in the temporal lobes of the cerebral cortex on both sides

  
• Damage was fairly extensive, but one specific region/structure was seriously damaged in all cases – the hippocampus (or hippocampi, since there are two – one on each side)
• Hippocampus


  An infolding of the cerebral cortex along the inner edge of the temporal lobe
• Almost all of the hippocampus on both sides + neighboring cortical regions (entorhinal, perirhinal and parahippocampal cortex) were removed from HM's brain
• Hippocampus and AA


  • A key region in anterograde amnesia: damage it and long term declarative memory formation is impaired, damage the neighboring regions and it isn't
• Damage to the hippocampus is not the only kind of damage that leads to amnesia
• Korsakoff's syndrome


  Caused by thiamine deficiency, usually as a result of long-term alcohol abuse, results in amnesia (both retrograde and anterograde) that affects declarative but not non-declarative memory
• The neuropathology in Korsakoff's syndrome is widespread, but there is relatively little effect on the hippocampus
• Regions damaged in Korsakoff's syndrome that are responsible for memory dysfunction are the mamillary bodies, the parts of the thalamus to which they connect, and regions of frontal cortex

  
• Damage to the hippocampus affects the acquisition of new declarative memories, but not new non-declarative memories