An international team of researchers has shown that when a group of people hear the same story or watch the same video, their heart rates tend to rise and fall in synch. This correlation of heart rates, described this month in Cell Reports, could one day lead to new tools for measuring attentiveness, both in the classroom and the clinic.
Lucas Parra, a biomedical engineer at City College of New York, New York, and co-senior author on the study, knew from the previous work by his own group and others that people paying attention to the same videos or listening to the same stories show similar brain activity, as measured by electroencephalogram (EEG). Jens Madsen, a postdoctoral fellow in Parra’s lab and cofirst author of the study, convinced him that the heart deserved a look as well. “Brain signals are hard to get,” says Parra. “If the heart can do that, it is even better because you don’t have to set up complicated recording equipment for the brain.”
The pair teamed up with co-senior author Jacobo Sitt of the Paris Brain Institute in France and others in a series of experiments to explore how heart rates increase and decrease across listeners. They began by asking over two dozen volunteers to each listen to 16 one-minute segments of Jules Verne’s “20,000 Leagues Under the Sea.” The heart rates of participants, captured by electrocardiogram (EKG), tended to speed up or slow down at the same points in the story.
The team then showed another set of volunteers a series of five short educational videos on topics ranging from the immune system to how light bulbs work. They then asked volunteers to watch the same videos a second time, but with the added distraction of attempting to count backwards silently in their minds by sevens while viewing. Without the distraction, viewers’ heart rates were correlated much like in the first study. With the added math challenge, attention waned and heart rates fell out of sync.
The researchers also found that people whose heart rates most closely correlated with others while listening to children’s stories were better at recalling details such as the names of characters. “If you are paying attention to the narrative, then your heart rate will fluctuate in a reliable fashion,” explains Parra. “If you stop paying attention, then your heart rate might still fluctuate, but not temporally aligned to the narrative.”
Exactly what caused heart rates to speed or slow with the stories wasn’t clear. When Parra saw the results of the first experiment, he thought that stories might affect breathing, which could affect heart rate. But subsequent experiments ruled out that possibility. For now, Parra’s best guess is that the brain is preparing the heart to always be at the ready. “I think that your heart rate goes up and down because your body needs to act,” Parra says. “That requires understanding what’s happening around us. And so that’s why the heart follows the narrative.”
On one level, the findings are uplifting simply because they demonstrate how stories unite us, says Parra. “It warms your heart to know that you are not alone when you’re listening to a story.”
But the findings do suggest applications. As part of the paper, the team also compared heart rates of healthy participants and patients with disorders of consciousness, such as coma, while listening to a children’s story through headphones. This small pilot study demonstrated that correlations among heart rates could help distinguish healthy participants from patients. Ultimately, the researchers would like to know whether heart rate fluctuations can suggest the potential for recovery. “In a patient that does in fact follow a story with the heart rate fluctuations,” Parra explains, “we would like to know if that is prognostic of their cognitive state in a month or three months from now.”
Neuropsychologist Hennric Jokeit, whose own research demonstrated correlations in heart rates across some viewers of a disaster film, agrees that the current study could spur new applications, from clinical diagnostics to advertising. “I think it’s an open field,” says Jokeit, who’s at the Swiss Epilepsy Centre in Zurich, Switzerland. Experimental psychologist Anne-Marie Brouwer envisions applications in education, such as evaluating how well educational material holds students’ attention. Brouwer, who conducts mental state monitoring research at the Netherlands Organisation for Applied Scientific Research, has shown in her own work that synchronous heart rates indicate attention to a story.
Parra thinks that one day students and others might use smart watches to track their own heart rates and give themselves a nudge whenever the fluctuation patterns indicate that they’re losing focus. His team is now gathering more data by showing participants full length movies. “What about the content pushes [heart rate] up and down?” Parra wonders. “Now perhaps we have enough diversity of material where we can start asking that kind of question.”