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Unlock This CourseThe case of HM (Henry Molaison) is one of the most famous and important studies in psychology. In 1953, a young man had brain surgery to treat his severe epilepsy. What happened next changed our understanding of memory forever. This case study, led by Brenda Milner and her colleagues, revealed crucial information about how our brains store and retrieve memories.
Key Definitions:
Henry Molaison (known as HM to protect his privacy) was born in 1926. He began having seizures at age 10 after a bicycle accident. By his twenties, his epilepsy was so severe that he couldn't work or live normally. Desperate for help, he agreed to experimental brain surgery in 1953.
Dr William Scoville performed the operation, removing parts of HM's temporal lobes, including most of his hippocampus, to stop the seizures. The surgery worked - HM's epilepsy improved dramatically. However, it had an unexpected and devastating side effect: HM could no longer form new memories.
After surgery, HM experienced severe anterograde amnesia. He could remember events from his childhood and early adulthood, but couldn't form new long-term memories. Every day was like starting fresh - he couldn't remember what he had for breakfast or recognise people he'd met the day before.
New factual memories, new personal experiences, ability to learn new information consciously
Childhood memories, basic skills, short-term memory (for about 20 seconds), personality
HM could still learn new motor skills, even though he couldn't remember learning them!
Milner and her team studied HM for over 50 years, making him the most studied patient in neuroscience history. Their research revealed that memory isn't just one system - it's made up of different types stored in different parts of the brain.
Brenda Milner, a neuropsychologist, began studying HM in 1955. She used various tests to understand exactly what had happened to his memory. Her careful, systematic approach set the standard for how we study brain-damaged patients today.
Milner used several innovative methods to test HM's different types of memory:
HM had to trace a star shape while looking at his hand in a mirror. This tested his ability to learn new motor skills. Amazingly, he got better each day, even though he couldn't remember doing the task before!
Milner tested HM's ability to remember word lists, stories and faces. These tests showed his severe problems with forming new declarative memories, whilst his short-term memory remained normal.
HM's case revolutionised our understanding of memory. Before this study, scientists thought memory was stored throughout the brain. HM's case proved that different types of memory are stored in different brain regions.
Milner's research with HM revealed that we have two main memory systems:
Facts and events you can consciously remember. Needs the hippocampus. HM lost this ability.
Skills and habits you do automatically. Stored elsewhere in the brain. HM kept this ability.
You can learn without being aware you're learning - HM proved this!
HM could learn to play new card games and get better at puzzles, but each time he played, he thought it was his first time. This showed that skill learning and conscious memory are completely separate brain systems.
HM's case proved that the hippocampus is essential for forming new declarative memories. Without it, information can't move from short-term to long-term memory storage.
Thanks to HM's case, we now understand the memory process:
Information enters short-term memory → hippocampus processes it → transfers to long-term storage in cortex → can be recalled later
Information enters short-term memory → damaged hippocampus can't process it → information is lost → no new long-term memories formed
HM's case raises important ethical questions about research with vulnerable participants. Although HM couldn't remember giving consent for studies, researchers had to consider his wellbeing carefully.
How do you get informed consent from someone who can't form new memories? Researchers had to re-explain studies each time and ensure HM wasn't distressed by the testing.
HM's case continues to influence psychology and neuroscience today. His contributions helped develop treatments for memory disorders and improved our understanding of conditions like Alzheimer's disease.
The case study revealed fundamental principles about memory that we still use today:
Different types of memory are stored in different brain areas
Essential for forming new declarative memories
Helps doctors understand and treat memory disorders
When HM died in 2008, he donated his brain to science. Researchers created a detailed 3D map of his brain, allowing future scientists to continue learning from his extraordinary case. His identity was finally revealed as Henry Molaison, honouring his massive contribution to our understanding of memory.