HM: Milner (1966)

• Background: 

  HM (Henry Molaison) underwent bilateral medial temporal lobectomy in 1953 to treat severe epilepsy. This surgery involved removing parts of his hippocampus, amygdala, and surrounding areas.
• Aim: 

  To investigate the effects of this surgery on HM's memory functions.
• Participant: 

  HM, a patient who had undergone brain surgery to treat epilepsy.
• Procedure: 

  Milner conducted various memory tests on HM over several years, including:

  1. Tests of short-term memory
  2. Tests of long-term memory formation
  3. Tests of procedural memory (motor skills)
• Short-term memory:

  • HM's short-term memory was largely intact.
  • He could hold information for brief periods (up to about 30 seconds).
• Long-term memory formation:

  • HM was unable to form new long-term declarative memories (anterograde amnesia).
  • He couldn't remember events that occurred after his surgery.
  • His memories from before the surgery were largely intact (some retrograde amnesia, but not complete).
• Procedural memory:

  • HM could learn new motor skills, despite not remembering the learning process.
  • He showed improvement in tasks like mirror drawing over time, even though he had no recollection of having done the task before.
• Intelligence and personality:

  • HM's general intelligence and personality remained intact.
• Conclusions:

  1. The medial temporal lobe, including the hippocampus, is crucial for forming new long-term declarative memories.
  2. Different types of memory (short-term, long-term declarative, and procedural) are stored in different parts of the brain.
  3. The ability to form new declarative memories is separate from other cognitive functions and types of memory.
• Implications:

  1. This study provided evidence for multiple memory systems in the brain.
  2. It highlighted the role of the hippocampus in memory formation.
  3. It demonstrated a dissociation between declarative and procedural memory.