When we listen to a story, our heart beats faster, sometimes slower, depending on the content – with all attentive listeners at similar points in the story, a study shows. The key factor here is that we focus on the narrative. Heart rate measurements could also provide information about the state of consciousness of patients in a coma or vegetative state. Patients whose hearts were beating faster at the appropriate points in a story had a better chance of regaining consciousness within six months.
When lovers look in the eyes, their hearts literally beat in sync. At an exciting point during a movie, the audience holds their breath together, and during an action-packed chase, the audience’s heartbeat collectively accelerates. Even in personal conversations and shared experiences, those involved often unconsciously synchronize their heartbeat and breathing. A team led by Pauline Pérez from the Paris Brain Institute has now examined the conditions under which such synchronization can occur and what can be derived from it.
Common heartbeat
“There is a lot of literature that shows that people synchronize their physiology with one another. But that assumes that you somehow interact with each other and are physically present in the same place, ”explains co-author Lucas Parra from the City College of New York. “We found that the phenomenon is much broader, and that just following a story and processing stimuli causes similar fluctuations in people’s heart rates. It is the cognitive function that drives the heart rate up or down. “
With four experiments, the researchers checked how exactly cognition affects the heart rate. “In all four experiments we presented the test subjects with narrative stimuli and recorded their heartbeat in the ECG,” the researchers explain. In the first experiment, the subjects listened to parts of the audio book “20,000 Leagues Under the Sea” by Jules Verne. In fact, most of them showed an increase or decrease in heart rate at the same points in the narrative.
Synchronous without distraction
To rule out that this was primarily due to the emotional content of the narrative, the researchers repeated the experiment with instructional videos without emotional variations. Here, too, the subjects’ heart rates showed similar fluctuations. If, on the other hand, the researchers distracted the test subjects by asking them to count backwards in their heads during the video, the synchronization of the heart rate turned out to be lower – even though the heart rate fluctuated significantly in this case as well. “Apparently, fluctuations and synchronization of the heart rate are independent phenomena,” say the researchers.
For the third experiment, subjects listened to children’s stories, either paying attention or being distracted. Here, too, a lack of attention meant that the heart rate was less adapted to the course of action, i.e. less synchronized. If the subjects remembered facts from the content after listening, those whose heart rate was particularly synchronized with the story did better. This not only showed the expected difference between distracted and attentive listeners. “Even if we only looked at the subjects who were not distracted, we found that the synchronization of the heart rate predicts memory performance,” the researchers report.
Apparently, the heart rate thus reflects how much a person deals with the narrative. The test subjects’ breathing rate, on the other hand, was not synchronized – even though it is known that breathing influences the heartbeat. “These results suggest that the effect of cognition on heart rate synchronization in this study cannot be explained by the synchronization of breathing,” the researchers write.
Attention even in a coma?
In the fourth experiment, the researchers examined not only healthy subjects but also 19 patients with impaired consciousness who were, for example, in a coma or a vegetative state. All subjects heard a ten-minute children’s story. “Contrary to what we expected, we found a higher variability of the heart rate in the patients with impaired consciousness than in the healthy control persons,” the researchers report. The synchronization of the heart rate in line with the story was, as expected, lower. Only two of 19 patients showed a statistically significant synchronization at all.
When the researchers re-examined the coma patients six months later, one of these two patients had regained consciousness. Of the other 17 patients, only one had regained consciousness over the six months but had lost his ability to speak. “These results suggest that heart rate synchronization could contain prognostic information, with an emphasis on conscious verbal processing,” the researchers write. Larger studies are now supposed to clarify to what extent an “audio book test” can actually provide information about the cognitive state of patients in a coma or vegetative state.
Source: Pauline Pérez (Paris Brain Institute) et al., Cell Reports, doi: 10.1016 / j.celrep.2021.109692