Scientists later realized that H.M., who also had a healthy parahippocampus, had similarly picked up a few choice facts after the 1953 surgery that destroyed his hippocampuses. H.M. loved doing crossword puzzles, and after seeing the clue a thousand times, he dimly recalled that “Salk vaccine target” equaled P-O-L-I-O. And through incessant references, H.M. retained a sliver of information about the 1969 moon landing and 1963 Kennedy assassination. Unlike all the people who, according to the cliché, knew exactly where they were when they learned those things, H.M. didn’t—that’s episodic memory. But he retained the basic fact.
In general, all memories are probably stored as personal memories initially: You might have first learned that Abraham Lincoln was the 16th president while on a field trip to Washington or more likely when you got that item wrong on a quiz and it got seared into your brain. After that, however, the memory gradually shifted to become semantic, and you retained only the more abstract knowledge that Abe = 16.
K.C. helped neuroscience come to grips with another important distinction in memory research, between recollection and familiarity. Colloquially, recollection means I specifically remember this, while familiarity means this sounds familiar, even if the details are fuzzy. And sure enough, the brain makes the same distinction. In one test, K.C.’s doctors compiled a list of words (El Niño, posse) that entered the common parlance after his accident in 1981. They then sprinkled those recent words into a list of pseudowords—strings of letters that looked like plausible words but that meant nothing. Time and again K.C. picked out the real word and did so with confidence. But when asked to define the word, he shrugged. From a list of common names he could pick out the names of famous people, even those who had become famous after 1981 (Bill Clinton). But he had no inkling what Clinton had done. In other words, K.C. found these terms familiar, even though specific recollection eluded him. This indicates that recollection once again requires the hippocampus, while a feeling of familiarity requires only certain patches of cortex.
K.C.’s memory loss also had the profound and paradoxical effect of wiping out his future. For the last three decades of his life, he couldn’t have told you what he planned to do over the next hour, the next day, the next year. He couldn’t even imagine those things.
It's not entirely clear why, but it probably runs deeper than K.C.'s inability to remember his plans. It's possible that the hippocampus is necessary to project yourself into the future and imagine personally experiencing things in the same way that the hippocampus allows you to put yourself back in time and re-experience the sights, sounds, and emotions of past memories. That's what your personal memories are really all about.
This loss of his future didn’t pain K.C.; he didn’t suffer or rue his fate. But in some ways that lack of suffering seems sad in itself.
Still, there’s one thing K.C. never lost—his sense of self, his sense of who he was deep down. He knew his own personality traits and knew where he came from. Knew his likes and dislikes and what he looked like in the mirror. Kent Cochrane always knew he was Kent Cochrane—not even severe trauma could take that away from him.
That’s actually a common theme in the neuroscience of accidents. It’s easy to see the victims of brain damage as reduced or diminished, and they are in some ways. But much of what they feel from moment to moment is exactly what you or I feel, and there’s almost nothing short of death that can make you forget who you are. Amid all the fascinating injuries in neuroscience history, you’ll come across a lot of tales of woe and heartbreak. But there’s an amazing amount of resiliency in the brain, too.