Date & Procedure: On September 1st, 1953, Dr. William Scoville performed a radical surgery on Henry Molaison (H.M.) to alleviate severe seizures.
Background: H.M. had suffered a childhood accident resulting in epilepsy, leading to frequent seizures, blackouts, and loss of control.
Surgical Procedure: Scoville removed H.M.'s hippocampus, a key part of the limbic system.
Immediate Results of the Surgery
Seizure Control: The operation reduced H.M.'s seizures greatly and did not impact his personality.
IQ Impact: H.M.'s IQ reportedly improved.
Memory Issues: H.M. lost the ability to form new memories and lost most memories from the previous decade.
Brenda Milner's Study
Research Objective: Sent by Wilder Penfield, Milner studied H.M. to understand his memory deficits.
Key Observations:
H.M. could retain information temporarily (e.g., memorizing a number for 15 minutes with constant repetition).
H.M. could not form long-term memories.
Memory Distinctions:
Short-term vs. Long-term Memory: Milner's work suggested that these are distinct, involving different brain regions.
Procedural vs. Declarative Memory: Milner demonstrated this separation using a star-tracing mirror task, showing that procedural memory (e.g., motor skills) could be intact despite deficits in declarative memory (e.g., facts and events).
Scientific Contributions and Legacy
Understanding Memory Formation:
Initial sensory data is processed in the cortex, then consolidated in the hippocampus, before being stored permanently back in the cortex.
H.M.'s case showed the critical role of the hippocampus in memory consolidation.
Procedural Memory:
Procedural memory, involving motor skills, relies on the basal ganglia and cerebellum, which were intact in H.M.
Legacy of H.M.
Lifelong Study: H.M. was studied extensively, contributing significantly to the field of neuroscience.
After Death: His brain was preserved and scanned, creating a digital map that contributed further to the study of memory.
Impact: Despite his condition, H.M.'s case has provided invaluable insights into the structure and function of memory, influencing generations of psychological and neurological research.