A few weeks ago, my boyfriend forgot the PIN to his debit card. A little weird, we agreed, but probably only temporary; sometimes, you just blank on things like that. But it’s now been nearly a month, and the memory of his PIN simply never came back. I was curious: How could such a familiar string of digits, one that he’d successfully stored and retrieved in his memory over and over for more than a decade, suddenly — and apparently permanently — disappear?
I emailed Eric Kandel, a neuropsychiatrist at Columbia University and a leading expert on memory storage; in 2000, he won a Nobel Prize for his work on the biological mechanisms of memory. In short, he knows what he’s talking about, and this question had actually been on his mind: As he explained in his response, his colleague Larry Squire, a neuroscientist at the University of California, San Diego, had recently forgotten his PIN in much the same way my boyfriend had.
The reason why we might forget something like a PIN once is fairly obvious, he said. After all, there are so many random strings of numbers competing for our memory bandwidth — Social Security numbers, addresses and ZIP codes, and so on. Usually, the forgetting is temporary. But, he explained, “it could become permanent” precisely, and paradoxically, because of the repeated unsuccessful attempts to remember.
Kandel elaborated further, drawing from Memory: From Mind to Molecules, the 2008 book he co-authored with Squire:
We describe a rather amazing phenomenon whereby bringing to mind information associated with a particular cue will inhibit the recall of other information associated with the same cue. It is not thought to be permanent but I believe the correct information could become very difficult to call up if a person continued to retrieve incorrect information.
He’s talking about retrieval cues, the little prompts we use to access information stored in our memories. The smell of lilacs might unconsciously remind you of your grandmother’s house and the flowers she planted outside, for instance. You can use cues to consciously jog your memory, too; for example, the name of an acquaintance might come to you more quickly if you call up the memory of the party where you met. Usually, for something like your PIN, the cue might be the visual of the ATM key pad or the debit card itself, but Kandel is saying that repeatedly forgetting your PIN may be essentially establishing a new retrieval cue pattern. So trying to recall your PIN only cues up the memory of the last time you tried and failed to recall your PIN.
It’s not exactly that the information has been deleted; the synaptic changes that represent the information are not “literally lost,” Kandel said (borrowing from his conversations with Squire). But it does appear to be possible to become stuck, at least for a time, in a kind of forgetfulness loop. The solution in my boyfriend’s case, after weeks of being unable to use his debit card, was to call his bank and order a new one, equipped with a brand-new PIN — hopefully one that he won’t forget.