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Henry Gustav Molaison (February 26, 1926 – December 2, 2008), known widely as H.M., was an American memory disorder patient who had a bilateral medial temporal lobectomy to surgically resect the anterior two thirds of his hippocampi, parahippocampal cortices, entorhinal cortices, piriform cortices, and amygdalae in an attempt to cure his epilepsy. Although the surgery was partially successful in controlling his epilepsy, a severe side effect was that he became unable to form new memories.

Henry Gustav Molaison
Henry Gustav 1.jpg
Molaison in 1953 before his surgery
Henry Gustav Molaison

February 26, 1926
DiedDecember 2, 2008(2008-12-02) (aged 82)

The surgery took place in 1953 and H.M. was widely studied from late 1957 until his death in 2008.[1][2] He resided in a care institute in Windsor Locks, Connecticut, where he was the subject of ongoing investigation.[3] His case played an important role in the development of theories that explain the link between brain function and memory, and in the development of cognitive neuropsychology, a branch of psychology that aims to understand how the structure and function of the brain relates to specific psychological processes.[citation needed]

Molaison's brain was kept at University of California, San Diego where it was sliced into histological sections on December 4, 2009.[4] It was later moved to The M.I.N.D. Institute at UC Davis.[5] The brain atlas constructed was made publicly available in 2014.[6][7]



Most of Molaison's two hippocampi were removed bilaterally.

Henry Molaison was born on February 26, 1926 in Manchester, Connecticut, and experienced intractable epilepsy that has sometimes been attributed to a bicycle accident at the age of seven. (This accident was initially reported to have occurred at age nine, but this was corrected by the patient's mother at a later stage.[8]) He had minor or partial seizures for many years, and then major or tonic-clonic seizures following his 16th birthday. In 1953, he was referred to William Beecher Scoville, a neurosurgeon at Hartford Hospital, for treatment.[2] He worked for a time on an assembly line but, by the age of 27, he had become so incapacitated by his seizures, despite high doses of anticonvulsant medication, that he could not work nor lead a normal life.

Scoville localized Molaison's epilepsy to his left and right medial temporal lobes (MTLs) and suggested their surgical resection as a treatment. On September 1, 1953, Scoville removed Molaison's medial temporal lobes on both hemispheres including the hippocampus and most of the amygdala and entorhinal cortex, the major sensory input to the hippocampus.[9] His hippocampi appeared entirely nonfunctional[when?] because the remaining 2 cm of hippocampal tissue appeared to have atrophied and some of his anterolateral temporal cortex was also destroyed.[citation needed]

After the surgery, which was partially successful in controlling his seizures, Molaison developed severe anterograde amnesia: although his working memory and procedural memory were intact, he could not commit new events to his explicit memory. According to some scientists, he was impaired in his ability to form new semantic knowledge.[10]

Researchers argue over the extent of this impairment. He also had moderate retrograde amnesia, and could not remember most events in the one- to two-year period before surgery, nor some events up to 11 years before, meaning that his amnesia was temporally graded.

His case was first reported by Scoville and Brenda Milner in 1957.[9]

Near the end of his life, Molaison regularly filled in crossword puzzles.[11] He was able to fill in answers to clues that referred to pre-1953 knowledge. For post-1953 information he was able to modify old memories with new information. For instance, he could add a memory about Jonas Salk by modifying his memory of polio.[1]

Insights into memory formationEdit



Nevertheless, imaging of Molaison's brain in the late 1990s revealed the extent of damage was more widespread than previous theories had accounted for, making it very hard to identify any one particular region or even isolated set of regions that were responsible for HM's deficits.[12]

Contribution to scienceEdit


Molaison's brain was the subject of an anatomical study funded by the Dana Foundation and the National Science Foundation. The aim of the project, headed by Jacopo Annese, of The Brain Observatory at UC San Diego, was to provide a complete microscopic survey of the entire brain to reveal the neurological basis of Molaison's historical memory impairment at cellular resolution. On December 4, 2009, Annese's group acquired 2401 brain slices, with only two damaged slices and 16 potentially problematic slices.[13] The digital 3D reconstruction of his brain was finished at the beginning of 2014.[14]

The results of the study were published in Nature Communications for January 2014. The researchers found, to their surprise, that half of H.M.'s hippocampus had survived the 1953 surgery, which has deep implications on past and future interpretations of H.M.'s neurobehavioral profile and of the previous literature describing H.M. as a 'pure' hippocampus lesion patient. Additionally, a previously unexpected discrete lesion was discovered in the prefrontal cortex. These findings suggest revisiting raw data from behavioral testing[citation needed]. A three-dimensional virtual model of the brain allowed the dynamics of the surgery to be reconstructed; it was found that the brain damage above the left orbit could have been created by Dr. Scoville when he lifted the frontal lobe to reach into the medial temporal lobes.

The article also describes the general neuropathological state of the brain via multiple imaging modalities. As H.M. was 82 when he died, his brain had aged considerably. Several pathological features were discovered, some severe, which had contributed to his cognitive decline.[15]




Despite his amnesic symptoms, Molaison performed quite normally in tests of intellectual ability, indicating that some memory functions (e.g., short-term memories, stores for words, phonemes, etc.) were not impaired by the surgery. However, for sentence-level language comprehension and production, Molaison exhibited the same deficits and sparing as in memory. Molaison was able to remember information over short intervals of time. This was tested in a working memory experiment involving the recall of previously presented numbers; in fact, his performance was no worse than that of control subjects (Smith & Kosslyn, 2007). This finding provides evidence that working memory does not rely on medial temporal structures. Molaison's largely intact word retrieval provides evidence that lexical memory is independent of the medial temporal structures.

Motor skill learningEdit

In addition to his intact working memory and intellectual abilities, studies of Molaison's ability to acquire new motor skills contributed to a demonstrated preserved motor learning (Corkin, 2002). In a study conducted by Milner in the early 1960s, Molaison acquired the new skill of drawing a figure by looking at its reflection in a mirror (Corkin, 2002). Further evidence for intact motor learning was provided in a study carried out by Corkin (1968). In this study, Molaison was tested on three motor learning tasks and demonstrated full motor learning abilities in all of them.


The dissociation of Molaison's implicit and explicit learning abilities along their underlying neural structures has served as an important contribution to our understanding of human memory: Long-term memories are not unitary and can be differentiated as being either declarative or non-declarative (Smith & Kosslyn, 2007).

Spatial memoryEdit

According to Corkin (2002), studies of Molaison's memory abilities have also provided insights regarding the neural structures responsible for spatial memory and processing of spatial information. Despite his general inability to form new episodic or factual long-term memories, as well as his heavy impairment on certain spatial memory tests, Molaison was able to draw a quite detailed map of the topographical layout of his residence. This finding is remarkable since Molaison had moved to the house five years after his surgery and hence, given his severe anterograde amnesia and insights from other cases, the common expectation was that the acquisition of topographical memories would have been impaired as well. Corkin (2002) hypothesized that Molaison “was able to construct a cognitive map of the spatial layout of his house as the result of daily locomotion from room to room” (p. 156).

Regarding the underlying neural structures, Corkin (2002) argues that Molaison's ability to acquire the floor plan is due to partly intact structures of his spatial processing network (e.g., the posterior part of his parahippocampal gyrus). In addition to his topographical memory, Molaison showed some learning in a picture memorization-recognition task, as well as in a famous faces recognition test, but in the latter only when he was provided with a phonemic cue. Molaison's positive performance in the picture recognition task might be due to spared parts of his ventral perirhinal cortex.

Furthermore, Corkin (2002) argues that despite Molaison's general inability to form new declarative memories, he seemed to be able to acquire small and impoverished pieces of information regarding public life (e.g., cued retrieval of celebrities' names). These findings underscore the importance of Molaison's spared extrahippocampal sites in semantic and recognition memory and enhance our understanding of the interrelations between the different medial temporal lobe structures. Molaison's heavy impairment in certain spatial tasks provides further evidence for the association of the hippocampus with spatial memory (Kolb & Whishaw, 1996).

Memory consolidationEdit

Another contribution of Molaison to understanding of human memory regards the neural structures of the memory consolidation process, which is responsible for forming stable long-term memories (Eysenck & Keane, 2005). Molaison displayed a temporally graded retrograde amnesia in the way that he "could still recall childhood memories, but he had difficulty remembering events that happened during the years immediately preceding the surgery".[16] His old memories were not impaired, whereas the ones relatively close to the surgery were. This is evidence that the older childhood memories do not rely on the medial temporal lobe, whereas the more recent long-term memories seem to do so[16]). The medial temporal structures, which were removed in the surgery, are hypothesized to be involved in the consolidation of memories in the way that "interactions between the medial temporal lobe and various lateral cortical regions are thought to store memories outside the medial temporal lobes by slowly forming direct links between the cortical representations of the experience".[17]

Post-death controversyEdit

On August 7, 2016, a New York Times article written by Luke Dittrich, grandson of Molaison's neurosurgeon William Beecher Scoville, raised a number of concerns about how Molaison's data and consent process had been conducted by the primary scientist investigating him, Suzanne Corkin. The article suggested that Corkin had destroyed research documents and data, and failed to obtain consent from Molaison's closest living kin.[18] In response to the article, a selection of neuroscientists signed a public letter arguing that the article was biased and misleading, and MIT published a rebuttal of some of the allegations in Dittrich's article.[19] This was in turn rebutted by Dittrich, who provided a recording of the interview with Dr. Corkin, where she said she had destroyed large amounts of data.[20]

See alsoEdit


  1. ^ a b Benedict Carey (December 6, 2010). "No Memory, but He Filled In the Blanks". New York Times. Retrieved December 5, 2008. Henry Gustav Molaison—known through most of his life only as H.M., to protect his privacy—became the most studied patient in the history of brain science after 1953, when an experimental brain operation left him, at age 27, unable to form new declarative memories. ... After repeated trials on the same puzzles, the man who lost his memory learned to fill in the right answers. 'We found that he could learn new semantic, factual information as long as he had something in his memory to anchor it to,' Dr. Skotko said.
  2. ^ a b Benedict Carey (December 4, 2008). "H. M., an Unforgettable Amnesiac, Dies at 82". New York Times. Retrieved December 5, 2008. In 1953, he underwent an experimental brain operation in Hartford to correct a seizure disorder, only to emerge from it fundamentally and irreparably changed. He developed a syndrome neurologists call profound amnesia. He had lost the ability to form new declarative memories.
  3. ^ Schaffhausen, Joanna. "Henry Right Now". The Day His World Stood Still. Archived from the original on February 9, 2008. Retrieved August 5, 2008.
  4. ^ Arielle Levin Becker (November 29, 2009). "Researchers To Study Pieces Of Unique Brain". The Hartford Courant.
  5. ^ Luke Dittrich (August 3, 2016). "The Brain That Couldn't Remember". The New York Times. Retrieved August 4, 2016.
  6. ^ Greg Miller (January 28, 2014). "Scientists Digitize Psychology's Most Famous Brain". Retrieved August 25, 2016.
  7. ^ a b "Patient HM". The Institute for Brain and Society. Retrieved August 25, 2016. Atlas available without charge on request.
  8. ^ Corkin, Suzanne (1984). "Lasting consequences of bilateral medial temporal lobectomy: Clinical course and experimental findings in H.M.". Seminars in Neurology. New York, NY: Thieme-Stratton Inc. 4 (4): 249–259. doi:10.1055/s-2008-1041556.
  9. ^ a b c William Beecher Scoville and Brenda Milner (1957). "Loss of recent memory after bilateral hippocampal lesions". Journal of Neurology, Neurosurgery, and Psychiatry. 20 (1): 11–21. doi:10.1136/jnnp.20.1.11. PMC 497229. PMID 13406589.
  10. ^ Schmolck, Kensinger, Corkin, & Squire, 2002
  11. ^ "The Man Who Couldn't Remember". NOVA scienceNOW. June 1, 2009. Retrieved December 9, 2010. In between it all he did puzzles, books upon books of them, a habit he’d picked up as a teenager. Near the end of his life he kept a crossword book and pen with him always, in a basket attached to his walker.
  12. ^ Corkin, Susanna; Amaral, David G.; González, R. Gilberto; Johnson, Keith A.; Hyman, Bradley T. (May 15, 1997). "H. M.'s Medial Temporal Lobe Lesion: Findings from Magnetic Resonance Imaging". The Journal of Neuroscience. 17 (10).
  13. ^ Worth, Rhian; Annese, Jacopo (2012). "Brain Observatory and the Continuing Study of H.M.: Interview with Jacopo Annese". Europe’s Journal of Psychology. 8 (2): 222–230. doi:10.5964/ejop.v8i2.475. ISSN 1841-0413.
  14. ^ Moll, Maryanne (January 29, 2014). "Henry Molaison's (or HM) brain digitized to show how amnesia affects the brain". TechTimes. Retrieved February 8, 2014.
  15. ^ Annese, Jacopo; Schenker-Ahmed, Natalie M.; Bartsch, Hauke; Maechler, Paul; Sheh, Colleen; Thomas, Natasha; Kayano, Junya; Ghatan, Alexander; Bresler, Noah; Frosch, MatthewP.; Klaming, Ruth; Corkin, Suzanne (2014). "Postmortem examination of patient H.M.'s brain based on histological sectioning and digital 3D reconstruction". Nature Communications. 5. doi:10.1038/ncomms4122. ISSN 2041-1723. PMC 3916843.
  16. ^ a b Smith_Kosslyn
  17. ^ Smith; et al. (2007). Cognitive Psychology: Mind and Brain. Upper Saddle River, NJ: Pearson/Prentice Hall. ISBN 0-13-182508-9.
  18. ^ Dittrich, Luke (August 7, 2016). "The Brain That Couldn't Remember". The New York Times. Retrieved March 26, 2018.
  19. ^ "Letters/Statement Submitted to the New York Times on August 9, 2016 from Prof. James J. Dicarlo, Head, Department of Brain and Cognitive Sciences at MIT". Department of Brain and Cognitive Sciences. Brain and Cognitive Sciences. August 9, 2016. Retrieved March 26, 2018.
  20. ^ Dittrich, Luke (August 10, 2016). "Questions & Answers about "Patient H.M."". Medium. Retrieved August 12, 2016.

Further readingEdit



  • M. W. Eysenck; M. T. Keane (2005). Cognitive Psychology: A Student’s Handbook (5th ed.). Hove, UK: Psychology Press. ISBN 0-86377-375-3.
  • E. E. Smith; S. M. Kosslyn (2007). Cognitive Psychology: Mind and Brain (1st ed.). Upper Saddle River, NJ: Pearson/Prentice Hall. ISBN 0-13-182508-9.
  • B. Kolb; I. Q. Whishaw; I. Q. (1996). Fundamentals of human neuropsychology (4th ed.). New York, NY: W. H. Freeman.

Full booksEdit

  • Suzanne Corkin (2013). Permanent Present Tense: The Unforgettable Life of the Amnesic Patient, H. M. ISBN 978-0465031597.
  • Luke Dittrich (2017). Patient H.M.: A Story of Memory, Madness, and Family Secrets. ISBN 978-0812982527.

External linksEdit