Forgetting as Important as Remembering

Why has Mother Nature put special cells in our brains that make us remember worse?

Reviewed by Michelle Quirk

Key points

• Until recently, memory researchers saw forgetfulness as the brain's inability to store new information.
• For the brain, memories have nothing to do with the past.
• In every moment, the brain pulls out the information it thinks is most relevant to help us act.

Every time I run around in my apartment looking for my lost keys, I curse my poor memory. The fact that I forgot where I put them is due to my brain not working as it should. That is at least what it feels like and, until recently, even memory researchers saw forgetfulness as the brain's inability to store new information.

But, in 2019, Japanese researchers studying mice discovered a group of brain cells that are active when the animals sleep.¹ These cells, which are also found in humans, have a strange property: They suppress activity in the brain's memory center, the hippocampus. It begs the question: Why has Mother Nature bothered to put special cells in our brains that make us remember worse?

We get a clue from the Russian journalist Solomon Shereshevsky (1886-1958), who in the history of medicine goes by the name "S." S is often considered to have had the best memory ever discovered in a human. It was enough for him to hear long strings of numbers and letters—even poems in languages ​​he did not speak—once to be able to recite them all perfectly. And even more impressive is that he remembered them flawlessly 15 years later!

However, there was one thing his brilliant memory could not handle—forgetting. S was inundated with details to the point that he had difficulty thinking abstractly. He had no problem reproducing long passages verbatim but had difficulty grasping wholes. The gist of the text somehow got lost in all the details. Moreover, each word evoked such a tidal wave of associations that he found it difficult to function in everyday life. Despondent that his brain was unable to let the most irrelevant details fall into oblivion, he wrote them down on a piece of paper that he burned, hoping that the details would go up in smoke as the words charred—needless to say, without any effect.

The curious case of S draws our attention to the difference between what we perceive as a good memory and what is a good memory to the brain. For you and me, good memory is about remembering details and being able to reproduce events exactly as they happened. But for the brain, memories have nothing to do with the past. Memories exist to guide us here and now. In every moment of our lives, the brain pulls out the information it thinks is most relevant to help us act in the moment. The brain must therefore be selective with what it stores—that is, remembers—as it would make us think too slowly if it constantly had to sift through an infinite amount of information. Further, the ability to think abstractly risks deteriorating if the brain is flooded with details, which is what happened to S.

As I write these words, I'm looking for an article about S. It's buried somewhere in the pile of manuscripts strewn across my desk. I have a hard time throwing things away and therefore a hard time finding them. The brain works the same way. Strangely enough, forgetting seems to be as important as remembering.