The Case of HM

Scientists learned a lot about the neuroanatomy of memory and amnesia more than half a century ago from the case of a young man in Connecticut (now famous in the medical literature as HM) who underwent brain surgery for relief from epileptic seizures. Taking desperate measures to stop the seizures, a Yale surgeon removed large portions of both medial temporal lobes, including the hippocampus, the amygdala, and the entorhinal and perirhinal cortices. The surgery controlled HM's epilepsy, but it left him with profound amnesia.

Although his procedural memory and his memory for events prior to the surgery were largely unaffected, HM was unable to learn new factual information or create new episodic memories. He described his experience in the following words: "Right now, I'm wondering, have I done or said anything amiss? 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."

erase the most central aspects of personal identity while sparing general functional capacity makes for an intriguing movie plot but does not make neurological sense.

In real life, people with amnesia caused by a concussive injury don't forget everything. They retain their general level of intelligence and a normal span of attention. They can form short-term memories lasting perhaps a few minutes, provided that there is no intervening interference. The breakdown primarily occurs with new fact learning and recall of episodic memories, which are formed and stored by the affected structures.

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