My episodic memory stinks. All my birthday parties are a blur of cake and presents. I’m notorious within my family for confusing the events of my own childhood with those of my siblings. I’m like the anti-Proust.

And yet, I have this one cinematic memory from high-school. I’m sitting at a Friday night football game (which, somewhat mysteriously, has come to resemble the Texas set of Friday Night Lights), watching the North Hollywood Huskies lose yet another game. I’m up in the last row of the bleachers with a bunch of friends, laughing, gossiping, dishing on AP tests. You know, the usual banter of freaks and geeks. But here is the crucial detail: In my autobiographical memory, we are all drinking from those slender glass bottles of Coca-Cola (the vintage kind), enjoying our swigs of sugary caffeine. Although I can’t remember much else about the night, I can vividly remember those sodas: the feel of the drink, the tang of the cola, the constant need to suppress burps.

It’s an admittedly odd detail for an otherwise logo free scene, as if Coke had paid for product placement in my brain. What makes it even more puzzling is that I know it didn’t happen, that there is no way we could have been drinking soda from glass bottles. Why not? Because the school banned glass containers. Unless I was willing to brazenly break the rules — and I was way too nerdy for that — I would have almost certainly been guzzling Coke from a big white styrofoam container, purchased for a dollar from the concession stand. It’s a less romantic image, for sure.

So where did this sentimental scene starring soda come from? My guess is a Coca-Cola ad, one of those lavishly produced clips in which the entire town is at the big football game and everyone is clean cut, good looking and holding a tasty Coke product. (You can find these stirring clips on YouTube.) The soda maker has long focused on such ads, in which the marketing message is less about the virtues of the product (who cares if Coke tastes better than Pepsi?) and more about associating the drink with a set of intensely pleasurable memories.

A new study, published in The Journal of Consumer Research, helps explain both the success of this marketing strategy and my flawed nostalgia for Coke. It turns out that vivid commercials are incredibly good at tricking the hippocampus (a center of long-term memory in the brain) into believing that the scene we just watched on television actually happened. And it happened to us.

The experiment went like this: 100 undergraduates were introduced to a new popcorn product called “Orville Redenbacher’s Gourmet Fresh Microwave Popcorn.” (No such product exists, but that’s the point.) Then, the students were randomly assigned to various advertisement conditions. Some subjects viewed low-imagery text ads, which described the delicious taste of this new snack food. Others watched a high-imagery commercial, in which they watched all sorts of happy people enjoying this popcorn in their living room. After viewing the ads, the students were then assigned to one of two rooms. In one room, they were given an unrelated survey. In the other room, however, they were given a sample of this fictional new popcorn to taste. (A different Orville Redenbacher popcorn was actually used.)

One week later, all the subjects were quizzed about their memory of the product. Here’s where things get disturbing: While students who saw the low-imagery ad were extremely unlikely to report having tried the popcorn, those who watched the slick commercial were just as likely to have said they tried the popcorn as those who actually did. Furthermore, their ratings of the product were as favorable as those who sampled the salty, buttery treat. Most troubling, perhaps, is that these subjects were extremely confident in these made-up memories. The delusion felt true. They didn’t like the popcorn because they’d seen a good ad. They liked the popcorn because it was delicious.

The scientists refer to this as the “false experience effect,” since the ads are slyly weaving fictional experiences into our very real lives. “Viewing the vivid advertisement created a false memory of eating the popcorn, despite the fact that eating the non-existent product would have been impossible,” write Priyali Rajagopal and Nicole Montgomery, the lead authors on the paper. “As a result, consumers need to be vigilant while processing high-imagery advertisements.”

At first glance, this experimental observation seems incongruous. How could a stupid commercial trick me into believing that I loved a product I’d never actually tasted? Or that I drank Coke out of glass bottles?

The answer returns us to a troubling recent theory known as memory reconsolidation. In essence, reconsolidation is rooted in the fact that every time we recall a memory we also remake it, subtly tweaking the neuronal details. Although we like to think of our memories as being immutable impressions, somehow separate from the act of remembering them, they aren’t. A memory is only as real as the last time you remembered it. What’s disturbing, of course, is that we can’t help but borrow many of our memories from elsewhere, so that the ad we watched on television becomes our own, part of that personal narrative we repeat and retell.

This idea, simple as it seems, requires us to completely re-imagine our assumptions about memory.  It reveals memory as a ceaseless process, not a repository of inert information. The recall is altered in the absence of the original stimulus, becoming less about what we actually remember and more about what we’d like to remember. It’s the difference between a “Save” and the “Save As” function. Our memories are a “Save As”: They are files that get rewritten every time we remember them, which is why the more we remember something, the less accurate the memory becomes. And so that pretty picture of popcorn becomes a taste we definitely remember, and that alluring soda commercial becomes a scene from my own life. We steal our stories from everywhere. Marketers, it turns out, are just really good at giving us stories we want to steal.

Image: irene/Flickr.