As far as A.K.P. could tell, everything he experienced had happened before. Every news headline, every episode of every show on TV, every visit from a friend, every conversation with his wife seemed to tickle the edges of memories that lay just out of reach. He'd heard of déjà vu, of course, but this sense of recognition seemed more pervasive, as if he were reliving an entire lifetime, recognizing every new moment as old news. A.K.P.'s doctors were baffled, until a young neuroscientist heard of the case and suggested that A.K.P. stop by for a visit.
"What's the point in seeing that guy again?" A.K.P. asked his wife. "He wasn't any help last time."
And so, the young neuroscientist came to them. His name was Chris Moulin, and he agreed to identify A.K.P. only by his initials, so long as the patient would allow him to publish his findings about the case. A.K.P. agreed, and Moulin began visiting the man and his wife at home. To Moulin's surprise, A.K.P. proved to be charming and sharp as a tack, except when it came to his recent memories. Because not only was A.K.P. plagued by incessant déjà vu; he was also prone to amnesia and had a tendency to fabricate facts to fill in the gaps.
One evening, Moulin asked A.K.P. why he'd switched off the TV.
"There's nothing but reruns on, as usual," said A.K.P.
"Oh?" said Moulin. "What's going to happen in that episode?"
"How should I know?" A.K.P. retorted. "I have a memory problem!"
It's the kind of silly "senior moment" story that anyone's parents or grandparents might pass around, but it begs some questions that aren't so easy to answer: How, exactly, do you (or I) know when something's familiar? How do we tell memory from fantasy? When we search our memories, how do we know for sure that we're not, like A.K.P., just making it up as we go along?
One way, of course, is to check our memories against external sources, like books and videos. This is especially helpful when it comes to semantic memories -- recollections of facts, figures, dates, and so on. But the facts aren't always so clear-cut when we call up episodic memories -- flashbacks of specific moments in our lives. Studies suggest that when we recall episodic memories, our brains replay a "compressed" version of the experience -- and with each new performance, details change. Some events get emphasized, whereas others get dropped from the script, sometimes never to return.
Want to see this process in action? Check out the infamous Selective Attention Test, and let me know how you score.
Weird, huh? It gets weirder. In labs all over the world, scientists are discovering ways to turn memories on and off with the flip of a switch, and even to transfer a "recognition" response from one brain to another. The result is what researchers are calling "hybrid memories" -- neural activity patterns that encode familiarity with brand-new places and experiences. So far this has only been demonstrated in mice, but I think A.K.P. would sympathize with the little guys.
"OK, sure," I hear you saying. "So it's easy to fudge the details of a short-term memory. Big deal. That doesn't mean my parents are imaginary, or that I never really won my third-grade spelling bee, or that I don't recognize a Fresh Prince rerun when I see one."
By and large, your intuition's probably right; after all, life would be pretty chaotic if no one's episodic memories lined up with anyone else's. But it's not always major memory glitches that pose the problem: Traumatic experiences, and sometimes even psychotherapy itself, can distort memories just enough to inspire false accusations. Every year, inaccurate and inconsistent eyewitness testimony continues to send innocent people to prison and let real criminals off the hook. Methods for identifying false memories continue to improve, but the days of hypnotized patients "recalling" ritual satanic abuse are apparently still not over.
So what's an honest eyewitness to do? The answer, which A.K.P. seems to've missed, is to stay a bit skeptical and remember that absence of evidence isn't evidence of absence. In other words, if you remember the sights, sounds, and smells of your first trip to the zoo, odds are you've been there, even if the elements of the memory are actually compressed from your memories of several trips. On the other hand, you might not have a specific memory of seeing the gorilla, but that doesn't necessarily mean he wasn't there.