Source: Hal McDonald

A couple of weeks ago, a Facebook friend tagged me in a throwback Thursday photo from an old high school year book. In the photo, a group of several classmates and I are posed on a stairway to immortalize some occasion or activity that I can’t for the life of me remember. The only notable thing about the picture is its sheer, black and white ordinariness—a group of high school kids staring into the camera with the sly smiles of students who have been called away from class for a few minutes in the middle of the day. As completely unremarkable as the photo was, it spawned a hailstorm of likes and comments that was way out of proportion to any real sentimental value the photo might have held for any of us. For a few hours that Thursday night, the comments section beneath the photo was awash in nostalgia—my own included—for that stray moment during a random school day four decades ago.

What most struck me about the experience was not the emotional reaction itself, but the fact that its trigger was a photograph that practically any one of us who liked or commented on it could see any time we wished by digging our old yearbook out of storage and flipping to the page on which the photo appeared. There was something about seeing it unexpectedly on Facebook, however, that transformed an ordinary black and white photograph into an intense moment of nostalgia.

Some insight into this experience can be found in a neuroimaging study recently conducted at Tokyo Metropolitan University. Several undergraduate students were shown photographs of objects they would have encountered on a regular basis during elementary school. As they viewed the photos, the students reported experiencing “highly nostalgic” feelings, and fMRI scans taken as they viewed the photos revealed two common denominators among these responses that shed some interesting light on my throwback Thursday experience.

The first of these had to do with expectation and volition. Since the students were not previously informed of the content of the pictures they would be seeing, their nostalgic reactions were associated with involuntary, rather than voluntary, autobiographical memories. In the same way that we enjoy listening to our music on shuffle, for example, and find it almost impossible to tickle ourselves, our autobiographical memories are never so powerful as when they sneak up on us unawares. Catching an unexpected glimpse of ourselves, or something relevant to us, in someone else’s old photo evokes memories that we would likely never be able to dredge up if we willfully searched for them.

A second consistent feature of the scans involved the “chronological remoteness” of the triggered memories, or how long it had been since the students last recalled the remembered experiences. Recall of long-forgotten memories activated parts of the brain involved in novelty detection, and the brain being wired to respond positively to stimuli that are new and unfamiliar, the distant memories provided a double reward—both for familiarity and for novelty.

Given these two components of nostalgic triggers, the photo of my classmates and me was nearly guaranteed to elicit nostalgia in anyone connected with it. Its appearance on Facebook was spontaneous and unexpected, making whatever autobiographical memories it triggered purely involuntary, and its sheer unadulterated ordinariness maximized its chronological remoteness by virtually assuring that none of us had given it a second thought in the forty years since it first graced the pages of our yearbook. It therefore unleashed in all of us a torrent of involuntary autobiographical memories that tickled our brains with both familiarity and novelty.

If evoking nostalgia is the purpose of a throwback Thursday post, the next time we’re looking for an old photo to share we would do well to keep in mind a simple black and white yearbook photo of a few bored high school students standing idly on a stairway.