Why did Henry Molaison undergo surgery in 1953, and who performed the operation?
A: To treat severe depression; performed by Brenda Milner at McGill University
B: To treat severe epilepsy; performed by neurosurgeon William Beecher Scoville
C: To treat a brain tumour; performed by a team at Yale School of Medicine
D: To treat chronic pain; performed by neurologist Wilder Penfield
Correct: To treat severe epilepsy; performed by neurosurgeon William Beecher Scoville
Henry Molaison had suffered from increasingly severe epileptic seizures since childhood, likely triggered by a bicycle accident at age nine. By his mid-twenties, his seizures were so frequent and debilitating that he could not hold down a job. Surgeon William Beecher Scoville performed an experimental bilateral medial temporal lobectomy at Hartford Hospital, removing the hippocampi and surrounding structures on both sides. The surgery did reduce the seizures -- but it also produced a profound and permanent memory impairment that Scoville and neuropsychologist Brenda Milner would spend years documenting.
After his surgery, H.M. developed a severe anterograde amnesia. What does "anterograde amnesia" mean?
A: The inability to recall memories formed before the onset of the amnesia
B: The inability to form new long-term memories after the onset of the amnesia
C: A complete loss of all memories, both past and present
D: Difficulty recognising familiar faces while retaining other memories intact
Correct: The inability to form new long-term memories after the onset of the amnesia
Anterograde amnesia refers to the inability to create new declarative (conscious) long-term memories following the event that caused the amnesia -- in H.M.'s case, his surgery. Every day he woke up not knowing what had happened the previous day, whom he had met, or where he was living. He would re-read the same magazine without any sense of having seen it before. This is distinct from retrograde amnesia (loss of pre-existing memories), though H.M. also had some retrograde amnesia for events in the years immediately before his surgery.
Despite being unable to form new declarative memories, H.M. showed normal learning on the mirror-drawing task over repeated sessions. What does this demonstrate?
A: That anterograde amnesia is not as severe as originally believed
B: That the hippocampus is required for all forms of learning and memory
C: A dissociation between declarative (explicit) and procedural (implicit) memory systems
D: That semantic memory is stored in the cerebellum rather than the hippocampus
Correct: A dissociation between declarative (explicit) and procedural (implicit) memory systems
In Brenda Milner's landmark mirror-drawing experiment, H.M. was asked each day to trace a star shape while only viewing his hand in a mirror -- a tricky motor task. Each morning he had no recollection of ever having done it before. Yet his performance steadily improved across sessions, just as it does in healthy participants. This was groundbreaking evidence that the brain contains at least two distinct memory systems: declarative memory (facts and episodes, which depends on the hippocampus) and procedural memory (motor skills and habits, which does not). H.M.'s hippocampi were gone, but his basal ganglia and cerebellum -- which support skill learning -- were intact.
Which brain structures were primarily removed during H.M.'s surgery?
A: The prefrontal cortex and anterior cingulate gyrus bilaterally
B: The bilateral hippocampi and surrounding medial temporal lobe tissue
C: The amygdala and thalamus on the left hemisphere only
D: The entire temporal lobe cortex bilaterally
Correct: The bilateral hippocampi and surrounding medial temporal lobe tissue
Scoville resected approximately 8 cm of medial temporal lobe tissue on each side, bilaterally. This included most of the hippocampus proper, the dentate gyrus, the subiculum, the entorhinal cortex, and much of the amygdala. The critical factor for H.M.'s amnesia was the bilateral destruction of hippocampal structures. Later research -- including a 2014 post-mortem MRI by Annese and colleagues that mapped the full extent of the lesion in microscopic detail -- confirmed that the damage was symmetric and extensive across the medial temporal lobes.
Which of the following memory abilities did H.M. retain relatively intact after his surgery?
A: Episodic memory for events occurring after 1953
B: Working memory (short-term holding of information) and remote semantic memory
C: The ability to learn new facts about public events and news
D: Autobiographical memory for his adult life prior to surgery
Correct: Working memory (short-term holding of information) and remote semantic memory
H.M. retained normal working memory -- he could hold a phone number in mind and repeat it immediately. He also retained remote long-term memories from his childhood and early life (before his surgery), and his general intelligence and semantic knowledge of the world as it stood in 1953. What he could not do was transfer information from working memory into new long-term declarative storage. He also had partial retrograde amnesia for roughly the decade before his surgery, suggesting the hippocampus plays a role in consolidating memories over time, not just encoding them.
Who was the neuropsychologist most responsible for systematically studying and documenting H.M.'s amnesia over decades?
A: Endel Tulving
B: Suzanne Corkin
C: Brenda Milner
D: Larry Squire
Correct: Brenda Milner
Brenda Milner, a British-Canadian neuropsychologist working at McGill University with Wilder Penfield, was the first scientist to rigorously test and document H.M.'s memory impairment. Her 1957 paper with Scoville is one of the most cited in all of neuroscience. She continued studying H.M. for years and is credited with establishing the key distinction between declarative and procedural memory through her mirror-drawing experiments. Suzanne Corkin at MIT later took over as H.M.'s primary researcher and cared for his scientific legacy until his death in 2008, when his full name was finally made public.
H.M.'s case helped establish the "standard model" of memory consolidation. What does this model propose?
A: All long-term memories are stored permanently in the hippocampus
B: The hippocampus temporarily holds memories that are gradually transferred to neocortical storage
C: Memories are stored in distributed networks across the entire brain from the moment of encoding
D: Only emotional memories require the hippocampus; neutral memories are stored in the frontal lobe
Correct: The hippocampus temporarily holds memories that are gradually transferred to neocortical storage
The standard model of systems consolidation proposes that new memories are initially dependent on the hippocampus, which binds together the distributed cortical representations of an experience. Over time -- through repeated reactivation during sleep and rest -- these memories become progressively encoded in neocortical networks and no longer require hippocampal involvement. H.M.'s preserved remote memories from childhood but impaired recent memories supported this model: his old memories had already been consolidated to neocortex, but events from the years just before surgery had not yet fully consolidated when his hippocampi were removed.
H.M.'s identity was kept confidential throughout his lifetime. When was his full name revealed, and what was it?
A: In 2000, when he consented to a documentary; his name was Howard Malcolm
B: In 2008, after his death; his name was Henry Gustav Molaison
C: In 1997, when he entered full-time care; his name was Herbert Michael Holt
D: His identity was never formally disclosed; H.M. remains his legal designation
Correct: In 2008, after his death; his name was Henry Gustav Molaison
Henry Molaison died on 2 December 2008 at the age of 82, in a nursing care facility in Windsor Locks, Connecticut. His full name was disclosed publicly by his researcher Suzanne Corkin shortly after his death. For over fifty years, protecting his privacy had been standard practice in research ethics -- he had not consented to having his identity known during his lifetime, and given the nature of his amnesia, his capacity to give informed consent was itself a complex issue. After his death, his brain was donated to science and sectioned into thousands of histological slices, creating a permanent record for future researchers.
Patient H.M. and the Hippocampus
Why did Henry Molaison undergo surgery in 1953, and who performed the operation?
About this quiz
Henry Gustav Molaison -- known to science for decades only as "H.M." -- became the most studied individual in the history of neuroscience after a single surgical procedure changed our understanding of memory forever.
In 1953, surgeon William Beecher Scoville removed large portions of H.M.'s medial temporal lobes, including both hippocampi, in an attempt to relieve his severe epilepsy. The surgery worked -- but it also left H.M. unable to form new long-term memories for the rest of his life. His case drew a sharp line between different memory systems and established the hippocampus as essential to declarative memory consolidation.