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Do you remember what you did last Tuesday before breakfast? Probably not.
Memory is a precious resource. And long-term memory is even more precious. We remember a fair amount of details of our experiences for a couple of minutes or maybe hours. But the vast majority of these details are gone in a week or so.
An extremely important question, then, is what determines whether an experience is committed to long-term memory. We do know a fair amount about long-term memory consolidation. We know, for example, that fragile memories are transferred to long-term storage during sleep. That is one of the reasons why sleeping is so important—a lack of sleep severely limits memory consolidation. But a crucial piece of the puzzle about just which experiences have the privilege to become long-term memories has just been revealed in a recent study.
One of the most important brain regions that is involved in memory management is the hippocampus. An easy-to-spot activity in the hippocampus is the so-called "sharp wave-ripple," which just means that a significant proportion, about 15 percent, of all the neurons in the hippocampus fire almost simultaneously. This sharp wave-ripple activity happens during sleep when memories are transferred to long-term memory. All this has been known.
The new finding suggests that the very same firing pattern also happens during the day right after memories are formed. What's more, there is a very simple correlation between the frequency of these sharp wave-ripple events during memory formation and the likelihood that the memory is transferred to long-term memory at night. The more sharp wave-ripples we get after an experience, the more likely it is that we'll remember this experience.
The prevalence of this relatively large-scale neural event, which is reasonably easy to capture with brain imaging, makes it easier to pinpoint which of our experiences make it into our long-term memory. It seems that the main factor that influences which experiences make it and which ones will be forgotten forever is whether the experience is followed by an idle period when the subject does very little.
The sharp wave-ripples during the day do not happen while the remembered experience is still going on. No, they happen in an idle period right after the experience. If there is no idle period following the experience, there is no time window for the sharp wave-ripples and, as a result, less chance that the experience will be remembered long-term.
These findings have far-reaching consequences. Idle periods, in our age of smartphones and social media, are precious commodities. We are very rarely idle as long as we have our phones for scrolling our social media feed, which is the exact opposite of an idle period.
As a result, regardless of how strong or meaningful an experience may have been, fewer sharp wave-ripples will happen in its immediate aftermath and then these sharp wave-ripples can't be replayed during sleep. This means they will likely not be committed to long-term memory.
What follows from this is that if you don't want to forget something nice that has happened to you, you probably shouldn't post about it on social media immediately afterward. Nor should you WhatsApp your friends about it. You should probably just sit down on a bench in a park and do nothing.
Idleness may not be a virtue, but it is a necessary step towards having long-lasting memories of things worth remembering.
