| 6s | |
| 9s | William Scoville used a hand crank and a cheap drill saw |
| 13s | to bore into a young man's skull, cutting away vital pieces of his brain |
| 17s | and sucking them out through a metal tube. |
| 20s | But this wasn't a scene from a horror film or a gruesome police report. |
| 25s | Dr. Scoville was one of the most renowned neurosurgeons of his time, |
| 29s | and the young man was Henry Molaison, the famous patient known as "H.M.", |
| 35s | whose case provided amazing insights into how our brains work. |
| 40s | As a boy, Henry had cracked his skull in an accident |
| 43s | and soon began having seizures, blacking out and losing control of bodily functions. |
| 49s | After enduring years of frequent episodes, and even dropping out of high school, |
| 53s | the desperate young man had turned to Dr. Scoville, |
| 57s | a daredevil known for risky surgeries. |
| 60s | Partial lobotomies had been used for decades to treat mental patients |
| 64s | based on the notion that mental functions were strictly localized |
| 67s | to corresponding brain areas. |
| 70s | Having successfully used them to reduce seizures in psychotics, |
| 74s | Scoville decided to remove H.M.'s hippocampus, |
| 77s | a part of the limbic system that was associated with emotion |
| 81s | but whose function was unknown. |
| 83s | At first glance, the operation had succeeded. |
| 86s | H.M.'s seizures virtually disappeared, with no change in personality, |
| 90s | and his IQ even improved. |
| 92s | But there was one problem: His memory was shot. |
| 96s | Besides losing most of his memories from the previous decade, |
| 99s | H.M. was unable to form new ones, forgetting what day it was, |
| 103s | repeating comments, and even eating multiple meals in a row. |
| 108s | When Scoville informed another expert, Wilder Penfield, of the results, |
| 112s | he sent a Ph.D student named Brenda Milner to study H.M. at his parents' home, |
| 117s | where he now spent his days doing odd chores, |
| 120s | and watching classic movies for the first time, over and over. |
| 124s | What she discovered through a series of tests and interviews |
| 127s | didn't just contribute greatly to the study of memory. |
| 130s | It redefined what memory even meant. |
| 133s | One of Milner's findings shed light on the obvious fact |
| 136s | that although H.M. couldn't form new memories, he still retained information |
| 141s | long enough from moment to moment to finish a sentence or find the bathroom. |
| 146s | When Milner gave him a random number, |
| 148s | he managed to remember it for fifteen minutes |
| 151s | by repeating it to himself constantly. |
| 153s | But only five minutes later, he forgot the test had even taken place. |
| 158s | Neuroscientists had though of memory as monolithic, |
| 161s | all of it essentially the same and stored throughout the brain. |
| 165s | Milner's results were not only the first clue for the now familiar distinction |
| 169s | between short-term and long-term memory, |
| 172s | but show that each uses different brain regions. |
| 176s | We now know that memory formation involves several steps. |
| 179s | After immediate sensory data is temporarily transcribed by neurons in the cortex, |
| 184s | it travels to the hippocampus, |
| 186s | where special proteins work to strengthen the cortical synaptic connections. |
| 192s | If the experience was strong enough, |
| 193s | or we recall it periodically in the first few days, |
| 196s | the hippocampus then transfers the memory back to the cortex for permanent storage. |
| 202s | H.M.'s mind could form the initial impressions, |
| 205s | but without a hippocampus to perform this memory consolidation, |
| 209s | they eroded, like messages scrawled in sand. |
| 213s | But this was not the only memory distinction Milner found. |
| 216s | In a now famous experiment, she asked H.M. to trace a third star |
| 221s | in the narrow space between the outlines of two concentric ones |
| 225s | while he could only see his paper and pencil through a mirror. |
| 229s | Like anyone else performing such an awkward task for the first time, |
| 232s | |
| 234s | But surprisingly, he improved over repeated trials, |
| 237s | even though he had no memory of previous attempts. |
| 241s | His unconscious motor centers remembered what the conscious mind had forgotten. |
| 246s | What Milner had discovered was that the declarative memory of names, dates and facts |
| 251s | is different from the procedural memory of riding a bicycle or signing your name. |
| 257s | And we now know that procedural memory |
| 259s | relies more on the basal ganglia and cerebellum, |
| 262s | structures that were intact in H.M.'s brain. |
| 266s | This distinction between "knowing that" and "knowing how" |
| 269s | has underpinned all memory research since. |
| 272s | H.M. died at the age of 82 after a mostly peaceful life in a nursing home. |
| 278s | Over the years, he had been examined by more than 100 neuroscientists, |
| 282s | making his the most studied mind in history. |
| 285s | Upon his death, his brain was preserved and scanned |
| 288s | before being cut into over 2000 individual slices |
| 292s | and photographed to form a digital map down to the level of individual neurons, |
| 297s | all in a live broadcast watched by 400,000 people. |
| 302s | Though H.M. spent most of his life forgetting things, |
| 304s | he and his contributions to our understanding of memory |
| 307s | will be remembered for generations to come. |
