Films Can Synchronize Viewers’ Heartbeats, Even If They Don’t Watch Together

When people watch a film or listen to a recording in the same room, strange things happen to their physiology. In repeated studies, scientists have noted that such social activities –or even having a conversation with another person – can induce synchronization between participants’ brain activity and heart rate. This phenomenon has long been assumed to originate from shared emotions being passed between observers, a sign of our inherently social brains.

Now, a new study suggests that we can experience synchronization together, even when we observe something alone.

The research, published in Cell Reports, is a collaboration between scientists at the City College of New York (CCNY), the Paris Brain Institute and French national research institute, Inserm.

“There's a lot of literature demonstrating that people synchronize their physiology with each other. But the premise is that somehow you're interacting and physically present the same place,” said co-senior author and CCNY professor Lucas C. Parra in a press release. “What we have found is that the phenomenon is much broader, and that simply following a story and processing stimulus will cause similar fluctuations in people’s heart rates. It's the cognitive function that drives your heart rate up or down.”

The research looked at how heart rates in participants watching short films or listening to audio books changed in response to different sections of the narrative. Over four experiments, the team teased out new findings about the human experience that may even have benefits for people in unresponsive states.

Volunteers and Verne

In their first experiment, the team played healthy volunteers samples of an audiobook – Jules Verne’s 20,000 Leagues Under the Sea. Electrocardiogram measurements recorded their heart rate as they listened. Despite each volunteer listening in separate sessions, with no interaction with other participants, 17 of the 27 participants’ heart rates correlated, meaning they increased and decreased over similar points in the recording.

The researchers hypothesized that feedback from cognition was driving these changes and wanted to see whether another measure of cognition – memory and attention – would match the changes in heart rate. The participants were asked to watch short instructional videos in two conditions, either at rest or while counting backwards in their heads. In this second, more distracted condition, heart rate synchronization between individuals dropped in all but one of the participants.

Importantly, these second videos were emotionally uninteresting, showing that the synchronization was not driven by the tension and emotion of Verne’s narrative.

To further test attention, the participants were asked to listen to short children’s stories, again while either at rest or during distraction, and then recall details from the recordings. As expected, volunteers who showed more synchronization – a sign of engagement with the story – were better at recalling details.

Correlations and consciousness

A final study took a more practical approach. People with disorders of consciousness, such as coma or a minimally conscious state, can remain in an unresponsive state for years, with some being able to perceive details of the world around them and others able to fully recover consciousness after extended periods.  Predicting which patients are in which category, however, is a difficult task. The researchers hoped that by playing audiobook recordings to hospital patients with consciousness disorders and measuring their heartbeat, prognosis might be predicted.

As expected, the patients showed far less synchronization than healthy volunteers. Interestingly, just 2 out of 19 patients showed any ability to synchronize to the recordings. At a six-month follow-up period, one of these two patients had passed away, whereas the other had fully regained consciousness and speech. Of the remaining 17, just one non-synchronizing patient had woken up, though they were unable to speak.

“This study is still very preliminary, but you can imagine this being an easy test that could be implemented to measure brain function,” said co-senior author Jacobo Sitt, a researcher at the Paris Brain Institute and Inserm. “It doesn’t require a lot of equipment. It even could be performed in an ambulance on the way to the hospital.”

Nonetheless, the technique was ineffective at distinguishing between patients with different levels of consciousness, suggesting further research and correlation with brain functions tests, like functional magnetic resonance imaging (fMRI) scans will be required to validate the tests more fully. Regardless, the work reveals new ways in which stories can affect our physiology via our brain function – showing how intimately the two are connected. “Neuroscience is opening up in terms of thinking of the brain as part of an actual anatomical, physical body,” said Parra. “This research is a step in the direction of looking at the brain-body connection more broadly, in terms of how the brain affects the body.”

Reference: 

Pérez P, Madsen J, Banellis L, et al. Conscious processing of narrative stimuli synchronizes heart rate between individuals. Cell Rep. 2020;36.  doi:10.1016/j.celrep.2021.109692