Poor Solomon Shereshevsky couldn’t help but create detailed memories of nearly everything that entered his unusual brain. He never forgot. He could be given long lists of numbers, words, and non-sense syllables and remember them perfectly years later—and backwards, no less.

While that talent seems like a blessing, and it certainly was responsible for his career as a mnemonist and showman, the neuro-physiologist Alexander Luria, who studied Shereshevsky in the 1920s, found that he was handicapped by this remarkable ability. Every experience, even the most mundane, consisted of the reliving of countless associated details. The simple act of asking a street vendor for a scoop of ice cream brought forth remembered imagery of such intensity that the transaction was quickly brought to a halt. Intelligence tests revealed an average IQ, yet interestingly, Shereshevsky could not easily create abstract thought. The level of detail that plagued his conscious attention precluded him from forming general principles by which to conduct a normal and happy life.

So, why do the rest of us forget? Why is memory transient —here today, faint in a few weeks, gone in a year or two? Is transience due to faulty wiring or the cellular limitations of the brain? Maybe it’s just like the old marketing joke about bad software code, except in this case it’s true—forgetting is not a bug, it’s a feature. Are there different types of memory? How does a brain store memory and what can be done to improve it?

Beginning with psychological research in the 1870s and leading up to the very latest theories and working models, this paper examines the key discoveries of the most influential experimental psychologists. Over many decades of toil, their work has revealed how we learn and remember—perhaps the biological activity that makes us most human. As Noble Prize winning neurobiologist, Eric Kandel proclaims,

“For me, learning and memory have proven to be endlessly fascinating mental processes because they address one of the fundamental features of human activity: our ability to acquire new ideas from experience and to retain these ideas in memory. In fact, most of the ideas we have about the world and our civilization we have learned so that we are who we are in good measure because of what we have learned and what we remember.” —Erik Kandel, Nobel Prize Lecture, 2000