Last week, I spent 3 hours under general anesthesia (while receiving a cochlear implant). Being a curious psychological scientist, and knowing my anesthesiologist, I seized the opportunity for a simple memory test.
First, the reason for my curiosity: A complete night’s sleep serves to process our day’s experiences for permanent memory storage. To sleep well is to remember. Nevertheless, the initial neural recording (the “encoding”) of memories takes a bit of waking time. Rats in experiments will therefore forget what they’ve just experienced if their memory formation gets interrupted with an electric current passed through their brain.
Humans are similarly amnesic for what they experience in the moments before receiving electroconvulsive therapy (ECT). And, as I’ve explained in my psychology texts, “Football players and boxers momentarily knocked unconscious typically have no memory of events just before the knockout.”
Would the same be true for someone falling asleep, or for someone lapsing into a drug-induced temporary coma? Are you amnesic for what you were thinking or experiencing just before nodding off?
To enable my experiencing an answer, my anesthesiologist alerted me to his drug administration, indicating that I would soon experience mental lights out. That was my signal to start counting the seconds out loud: “1, 2, 3, . . .”
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On awakening 3.5 hours later, I remembered the trip into the operating room and onto the operating bed. I remembered chatting with the attending staff. I remembered the anesthesiologist connecting the bodily sensors . . . but nothing thereafter.
In reality, I learned on awakening, my unremembered conscious engagement continued for about 3 minutes, including my counting to 16. A segment of my life—fully experienced but unrecorded—had vanished into the mind’s black hole.
It was a weird experience. But weirder yet is what I have underappreciated until now: that I—and you—experience this fascinating phenomenon daily.
An anesthesia-induced coma is not sleep (and may also be complicated by an amnesic drug effect). Nevertheless, last month when I proposed my anticipated quasi experiment to Baylor University sleep researcher Michael Scullin, he predicted my experience. The expected memory loss, he said, would be an example of (a new concept to me) mesograde amnesia.[i]
We routinely but unknowingly experience mesograde amnesia as our immediate pre-sleep experience falls into oblivion. The phenomenon was demonstrated in a 1997 experiment by James Wyatt and colleagues: People failed to recall words spoken to them shortly before an EEG recording detected their transition to sleep. (The memory loss—from up to 4 minutes before sleep commenced—was, like mine on the operating table, surprisingly long.)
Weirder yet, as Scullin further explained, sleep-induced mesograde amnesia implies that you and I will typically not remember our short (1- to 4-minute) awakenings during our night—a phenomenon also experimentally confirmed. Thus, university students who send a text message while briefly awake will, the next morning, often have no memory of doing so. And sleep apnea patients will experience multiple brief awakenings without remembering them.
Mesograde amnesia explains one of my own recent sleep experiences. As I slipped into bed alone on a recent warm night, I pushed the blanket down to my feet. The room cooled during the night, and in the morning I awoke to find the blanket pulled up—with my having no memory of how that happened. Had my fairy godmother noticed my chill?
Scullin’s memory tutorial also led to my wondering about an evening after-work experience I have at least weekly—briefly nodding off while watching a British mystery. When I snap back to consciousness, I typically need to replay about 10 minutes for which I have no memory. I’ve assumed that the program gap represents a 10-minute nap. In reality, I now realize, 4 minutes of mesograde amnesia plus 6 minutes of napping could account for the missing 10 minutes.
What’s true for the sleep-experiment participants, and for me, is also true of you. Your falling asleep—at the beginning of your sleeping or napping, and again during your interrupted sleep—makes you amnesic for your immediately preceding life experience. Over time, your mesograde amnesia experiences add up to hours of your conscious life that have vanished, having gone unrecorded on your cerebral hard drive.
Count it as one more example of our wonder-full lives. (For more such wonders, see my just-published How Do We Know Ourselves: Curiosities and Marvels of the Human Mind. 😊)
[i] Most amnesia is either anterograde (trouble making new memories) or retrograde (trouble accessing old memories). Mesograde (middle grade) amnesia is not clearly due to either the inability to store a new memory or retrieve the memory once stored. Some say it is produced by memory-disruptive bursts of hippocampal activity during the wake-to-sleep transition.
