HM: Milner (1966)

• Aim:

  To investigate the effects of hippocampal removal on various aspects of memory and cognitive function.
• Participant:

  HM, who underwent experimental surgery removing tissue from the medial temporal lobe.
• Data Collection Methods:

  • Psychometric testing (IQ testing).
  • Direct observation of behavior.
  • Interviews with HM and family.
  • Cognitive testing (memory recall and learning tasks).
• MRI Scan:

  Later conducted by Corkin to assess brain damage
• • Key Findings:
  • HM had anterograde amnesia, unable to form new episodic and semantic memories.
  • Retained motor skills (procedural memory) and showed improvements in new skills without memory of learning them.
• Results:

  1. HM was unable to form new episodic (event) or semantic (fact-based) memories after the surgery.
  2. Intact Procedural Memory: HM showed improvement in motor skills, such as the mirror-drawing task, despite no conscious recollection of having practiced.
  3. Preserved Intelligence: HM's general intelligence and personality remained intact.
  4. Retrograde Amnesia: HM experienced partial memory loss for events preceding the surgery, with more recent memories being more affected.
• Milner's study on HM provides valuable insights into memory formation, the role of the hippocampus, and the complexity of memory systems in the brain.
• Study Background: 

  Henry Molaison (HM) underwent bilateral medial temporal lobe resection, including the removal of his hippocampus, to treat severe epilepsy. This surgery inadvertently created a unique opportunity to study the role of the hippocampus in memory formation.
• Procedure:

  The researchers employed a multi-method approach:

  • Extensive neuropsychological testing
  • Direct behavioral observations
  • Interviews with HM and his family
  • Cognitive assessments, including memory and learning tasks

  Example

  One notable task was the mirror-drawing test, where HM was asked to trace a star while only able to see his hand and the star through a mirror. This task was repeated over several days.
• Conclusion:

  This study provided strong evidence for the localization of memory function in the brain:

  1. The hippocampus plays a crucial role in transferring information from short-term to long-term memory.
  2. Different types of memory (episodic, semantic, procedural) are processed and stored in distinct brain regions.
  3. The medial temporal lobe, particularly the hippocampus, is essential for the formation of new declarative memories but not for procedural learning or general intelligence.
• The HM case study revolutionized our understanding of memory systems in the brain and remains one of the most influential studies in cognitive neuroscience.