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“I don’t remember things,” Henry explained to the unfamiliar female interviewer. She seemed very curious about how he spends a typical day, and about what he had eaten for breakfast, but his efforts to summon the information from his mind were fruitless. He could easily answer her questions regarding his childhood and early adult years, but the indefinite expanse of time since then was bereft of memories. In fact, from moment to moment Henry feels almost as though he has just awakened from a deep sleep, with the fleeting remnants of a dream always just beyond his grasp. Each experience, dull or dramatic, evaporates from his memory within a few dozen heartbeats and leaves no trace.

For over fifty years Henry has lived with anterograde amnesia, a form of profound memory loss which prevents new events from reaching his long-term memory. As a result his only memories are those he possessed prior to his amnesia, and the small window of moments immediately preceding the present.

The amnesia frequently depicted in fiction is a very rare retrograde variety known as dissociative fugue, where one’s identity and all memories prior to the pivotal event are compromised. In contrast, anterograde amnesia does not deprive the sufferer of their identity, their past, or their skills; it merely prevents new memories from forming. As a consequence one’s final memories are frozen in perpetuity, often accompanied by a constant sensation that one has just awoken from an “unconscious” state which filled the intervening time.

Henry’s handicap is the unintended result of experimental brain surgery performed in 1953. In his late teens the highly intelligent student began to experience frequent grand mal seizures, characterized by loss of consciousness, muscle spasms, and rigidity. The frequency of these epileptic events increased to the point that he was stricken with spontaneous episodes of unconsciousness every few minutes. After exploring every other avenue known to contemporary medicine, Dr. William Scoville administered a radical resection of the man’s medial temporal lobes in a desperate bid to reclaim some quality of life for young Henry. In that respect the experimental operation was a success⁠— the patient’s severe seizures were reduced dramatically after the operation⁠— however the surgeon was distressed to discover that the removal of the hippocampi had stripped Henry of his ability to form new memories.

H.M. in situ MRI scan in the coronal plane

The development seriously hindered Henry from pursuing a normal life, but due to his condition he quickly became the world’s most famous subject in the study of the human brain. His real identity is a closely kept secret to this day, and he is referred to in medical literature by only his initials, “H.M.” However unfortunate, H.M.’s handicap helped to propel memory research beyond the realm of the philosophical for the first time in history. Earlier efforts to explore memory had been limited to animal studies, where scientists deliberately damaged various regions of lab animals’ brains to monitor any loss of memory functions. Such experiments were not only unpleasant for the animals, but frustratingly inconclusive for the researchers.

H.M. has been described as a friendly and articulate man with a higher-than-average IQ, sporting a charming personality in spite of his condition. Now in his early eighties, he still vividly recalls events from his childhood such as the stock market crash of 1929, but he is stricken with renewed grief every time he learns of his mother’s death. The grief is short-lived, however, as the substance of the news soon slips from the feeble grasp of his “working memory.” In an interview with researchers, he described the sensation:

“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.”

Like most anterograde amnesiacs, Henry experienced a degree of retrograde amnesia as well, blurring the details of the months leading up to the fateful operation.

Similar cases of anterograde amnesia have appeared over the years, often caused by Korsakoff’s Syndrome, a thiamine (vitamin B1) deficiency brought on by chronic alcoholism, malnutrition, eating disorders, or poisoning. This strongly suggests that thiamine is necessary to maintain the memory-writing features of the brain. Some abnormal viral infections can also produce the affliction, as is the case with a famed music expert named Clive Wearing. His ability to store memories was destroyed by a rogue infection of the herpes simplex 1 virus which attacked his brain’s hippocampus rather than triggering the typical cold sores. Other known causes include brain tumors, oxygen deprivation, and dementia-related diseases such as Alzheimer’s. In each instance it is found that the hippocampi have been compromised, indicating that these small structures are vital in laying down long-term memories. The hippocampus does not seem to play a role in recollection, however, since existing memories remain accessible.

Though anterograde amnesiacs are blocked from storing new information, researchers were astonished to discover that subjects are nonetheless capable of mastering new and complex tasks over time. Subjects who repeatedly practice skills such as backwards writing or guitar-playing can demonstrate measurable improvement, though in each instance the subject believes that he or she is attempting the task for the first time. This insight cast serious doubt upon the long-held belief that all memory is stored in a common mental reservoir. It also demonstrated that procedural memory⁠— the “how to” memory of motor skills⁠— is not governed by the exact same circuitry as episodic memory (autobiographical events) and semantic memory (general knowledge and facts). Additionally, some patients have experienced the Tetris Effect hours or days after playing the game during experiments; they describe vivid dreams of falling Tetris shapes though they possess no conscious memory of the game’s existence.

A diagram of one of Henry M's living spaces, and his depiction of it three years after moving out.

A neuroscientist named Suzanne Corkin has been following Henry’s M.’s progress for about forty-three years, but each time she introduces herself he greets her as though he is meeting her for the first time. One one occasion, however, a nurse mentioned to Henry that “Dr. Corkin” had been asking about him, and he responded by asking, “Suzanne?” Though he could not say who she was, he had somehow managed to associate her first and last name.

Over the years a modest amount of semantic information has actually managed to seep into Henry’s long-term memory, suggesting that his brain may be struggling to find alternate pathways with sporadic success. He knows that a president named John Kennedy was assassinated in 1963, and he can draw a roughly accurate diagram of a home where he lived for a few years following his surgery. Henry seems untroubled by the elderly face which stares back at him from the mirror, suggesting that he is unsurprised by the notion that decades that have passed since his life-changing operation. When asked what he thought about how he looked, he responded matter-of-factly, “I’m not a boy.” He also seems to have learned that his memory is broken and that scientists are studying him to discover more about the human mind. Once, when asked whether he is happy, Henry responded “Yes” without hesitation. He followed with, “the way I figure it is, what they find out about me helps them to help other people.”

Small talk with H.M. tends to be a bit repetitive, but occasionally revealing. During a visit to the Massachusetts Institute of Technology to conduct memory tests, Dr. Corkin asked Henry if he knew where he was as they strolled down a nondescript corridor. “Why of course,” he replied with a grin, “I’m at MIT!”

Taken aback, Dr. Corkin asked, “How do you know that?”

Laughing, Henry pointed at a nearby student wearing an MIT sweater. “Got you that time!”

Not only did the event demonstrate his intact sense of humor, but it showed that his powers of deduction are unhindered by his memory malady. On another occasion Henry was asked what he does to try to remember things. “Well,” he replied with a chuckle, “That I don’t know ’cause I don’t remember what I tried.”

H.M. undergoing testing at MIT

In a rare example of scientific correctness in Hollywood, the reality of anterograde amnesia was depicted with reasonable accuracy in the 2001 film Memento. The filmmakers applied the concept of reverse chronology to mimic the effects of the condition, allowing viewers to share in the protagonist’s confusion regarding prior events.

Owing to his unfortunate ailment Henry M. will never be able to understand the inestimable gift he has given to the field of neurology. The amnesic octogenarian presently resides in a Connecticut nursing home, where even today he continues to help researchers to coax secrets from the human mind. Furthermore, Henry’s lifelong contribution to science will not cease upon his death; he and his court-appointed guardian have agreed to donate his brain to science so that neurologists may one day examine the offending lesions in detail.

Though science still possesses a poor understanding of memory’s machinations, Henry and other sufferers of anterograde amnesia have provided a considerable number of indispensable clues. Their unwitting contributions will not be soon forgotten.

Update 02 December 2008, in memoriam: Sadly, the infamous and mysterious “H.M.” has passed on. R.I.P., Henry Gustav Molaison. This article has been updated with subsequently released photos of Henry.