H.M. and the Hippocampus – Sumaya Beri

H.M. and the Hippocampus – Sumaya Beri

~Sumaya Beri | 11C

In 1953, Henry Molaison (often referred to as H.M)  approached neurosurgeon WB Scoville with a case of epilepsy. What followed changed the trajectory of neuroscience forever. As was common in those days, Scoville performed a lobotomy, removing Molaison’s medial temporal lobes, including the hippocampi (on both sides of the brain), parts of the amygdalae and the entorhinal cortex to treat his seizures. The surgery proved somewhat successful in its aim. However, Molaison was no longer able to create new memories and was unable to recall the recent past- facing severe anterograde amnesia. In his words, “You see, at this moment everything looks clear to me, but what happened just before? That’s what worries me. It’s like waking from a dream. I just don’t remember.” When scientist Brenda Milner asked him to draw a star between two concentric stars looking at the pencil and paper through just a mirror, he failed. The big surprise was that over time, and after repeated trials, which he still had no memory of, he did eventually succeed. Clearly, his procedural memory had escaped unscathed. The unconsciously functioning motor cortex of his brain was operational, his conscious memory was not. The long-believed theory of memory being uniform and concentrated in a specific centre of the brain had been dismantled in one fell swoop by H.M and his peculiar case. Memory can be of various types- including implicit and explicit. Explicit memory ranges from semantic to episodic and depends on the hippocampus, neocortex and even the amygdala. Implicit memory such as motor and muscle memory on the other hand, is reliant on the basal ganglia and cerebellum. Henry’s implicit memory survived the removal of the hippocampi, but his explicit memory was ruined, and even as medicine progressed by the time he died at 82, his ability to transform and store short term memories was beyond repair. Evident from trials and experiments that delineated the difference between the kinds of memory, the removal of the hippocampi from Henry’s brain is what caused his anterograde amnesia. But what is the hippocampus and what does it do? The hippocampus is a seahorse-shaped structure embedded in both temporal lobes of the brain. In the case of episodic memory, when sensory data is temporarily received by the cortex, it then travels to the hippocampus. Specialised proteins (CREB, etc) strengthen the connections between the synapses (contact point between neurons to transfer information) in the cortex, and if the experience is important enough to be recalled periodically over a period of time, the memory is transferred back to the cortex, but for permanent storage this time. It is theorised that this transfer takes place while we sleep. In simple words, the hippocampus is a key player in memory consolidation following initial impressions (which were unaffected after Henry’s surgery), and though its removal deprived H.M of long term memories, it enriched our understanding of the brain as a whole to a magnificent extent. 


  1. https://www.youtube.com/watch?v=KkaXNvzE4pk
  2. https://www.youtube.com/watch?v=5EyaGR8GGhs
  3. https://qbi.uq.edu.au/brain-basics/memory/where-are-memories-stored
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548359/
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2649674/
  6. https://www.techtimes.com/articles/3026/20140129/henry-molaison-or-hm-brain-digitized-to-show-how-amnesia-affects-the-brain.htm
  7. https://www.termpaperwarehouse.com/essay-on/Living-In-The-Moment/293290

~Sumaya Beri | 11C

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