Amnesia

Psy315 - Class 16

(This page last updated 12 October, 2006.)

Retrograde Amnesia: Inability to remember events that occurred before the brain injury.

Anterograde Amnesia: Inability to remember events that occurred after the brain injury.

Patient H.M.

• epilepsy
• Treated in 1953 by removing hippocampus bilaterally and parts of temporal lobe surrounding it.
• After surgery, severe anterograde amnesia.
• Also weak retrograde amnesia.
• Amnesia persists to this day.
• Forms no new explicit long term memories.
  • Little or no memory of any events that have happened since his operation.
  • Retains memories for events before operation.
• Working memory unaffected.
  • Can carry on a normal conversation.

Function of the Hippocampus

• It is NOT where all old memories are stored.
• It does seem to be crucial for recording new explicit memories. The information is actually stored elsewhere in the brain, however.

Other Patients with Amnesia Caused by Brain Damage

• Anoxia
  • Lack of oxygen in the blood
• Ischemia
  • Lack of blood to the brain
• Korsakoff's Syndrome
  • Thiamine deficiency due to alcoholism
  • Does not damage the hippocampus, but does damage brain structures connected to the hippocampus that are also important to memory.
• Patient N.A.
  • Stab wound to the medial thalamus
• Clive Wearing
  • British musician
  • Viral encephalitis
    • Damaged hippocampus bilaterally
    • Also frontal lobe damage
  • Often feels like he has just become conscious.
  • Remembers his wife, but can no longer recall many important aspects of his life.
  • Can form no new episodic memories, and has little ability to acquire new semantic memories.
  • Retains his musical ability.

     

Implicit Memory not Affected by this Type of Amnesia

• Normal priming
  • Lexical decision
  • Word stem completion
• Normal procedural learning
  • Mirror reading
  • Mirror tracing
  • Note Clive Wearing's piano playing

Summary: Damage to the hippocampus and related brain structures impairs the ability to form new long-term explicit memories. It does not affect working memory or implicit memory.

Relevant Website

• Newspaper story about Clive and Deborah Wearing

next class: Remembering the Gist
  
Psych 315: Cognitive Psychology Kyle Cave Psychology Dept. U. Mass.