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Tom smiles uncertainly at Summer. They touch hands, a testament to their shared past. “This is a story of boy meets girl,” the narrator tells us, but it’s “not a love story.” It’s the opening scene in (500) Days of Summer, a 2009 romantic comedy starring Zooey Deschanel and Joseph Gordon-Levitt. After a brief intro, time cards flip rapidly on the screen, stopping at day 290. We find Tom in his kitchen, smashing plates. Summer has just broken up with him. Soon the numbers scroll again, and we return to the beginning, when they meet in an office elevator. Tom swoons. Then we are transported to the future once again, to the day when Tom realizes he is “officially” in love.
It’s a familiar narrative conceit. Storytellers of all kinds narrate events in nonlinear sequences, either for effect, to enhance the drama, or because they forgot some key detail and want to fill in the gaps. Even so, the jump cuts are disorienting. Because we live our lives chronologically, making sense of big leaps in a narrative sequence entails heftier mental work: Research shows our reaction times and reading pace slow and we have a harder time accessing memories related to events when they are presented to us out of order. So how do our brains actually process these narrative hops in chronology? That’s the question a team of Dartmouth researchers set out to answer in a small study recently published in Cerebral Cortex.
The Dartmouth team analyzed the fMRI scans of 20 healthy study participants, 19 to 53 years of age, taken as they watched (500) Days of Summer. What they found is evidence that our brains use temporal cues—like the time cards in the movie, or words related to the passing of time in a written or spoken story—to reorganize events into chronological order in real time. “I think the fact that we found evidence for this unscrambling on the fly during a complex narrative stimulus shows just how sensitive our brains are to temporal information,” says neuroscientist Emily Finn, a co-author of the study.
The brain is recognizing and sorting scenes that belong together in time.
To isolate the effects of time jumps, and compare them with changes in setting, the researchers tracked how certain areas of the brains of participants responded to changes in location and chronology. They chose to track activity in the 12 seconds following each narrative jump in certain areas of the brain that had already been associated with processing temporal and spatial context and integrating narrative information across long timescales.
Finn and her colleagues identified several specific brain areas that seemed especially sensitive to narrative hops in time, over and above changes in location. But even more interesting is that some of these brain areas maintained similar activity patterns for all chronologically related scenes, a finding that was consistent across participants. They took this as evidence that the brain is recognizing and sorting scenes that belong together in time.
An instant mastery over the chronology of events may serve a greater purpose, Finn and her colleagues reason: Encoding events in the correct order in our memories could be very helpful for understanding the causal relationships between one thing and another. The more you understand about cause and effect, the better you may be at predicting what is yet to come and making sense of the world and your environment, says Finn.
Of course, not all nonlinear narratives come with neat temporal cues. Sometimes, all you get is a passing “when I was a kid.” Other times, narrative fragments appear to spill into one another. In these cases, we may use other elements embedded in stories to sort out the chronology of cause and effect.
For example, Finn wondered if the familiar arc of the love story in (500) Days of Summer helped study participants put the disordered pieces where they belong. Many of the stories we tell each other and ourselves follow standard arcs, even if we have to leave out certain details to make the puzzle pieces fit.
The next time you are immersed in a movie or a book, know that your brain could be doing some behind-the-curtain work, constructing a whole from disjointed narrative parts, building a coherent world. 
Lead image: JMGDigital / Shutterstock
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