People listening to the same story synchronize their heart rates.

Several studies have shown that people paying attention to the same videos or listening to the same stories show similar brain activity, as measured by electroencephalogram (EEG). Electrocardiogram (EKG) measurements are experimentally much easier to perform. Pérez et al. now show that heart rates of participants of their study measured by EKG tended to speed up or slow down at the same points in the story, demonstrating that conscious processing of narrative stimuli synchronizes heart rate between individuals. Here is their abstract:  

Highlights

• Narrative stimuli can synchronize fluctuations of heart rate between individuals 

• This interpersonal synchronization is modulated by attention and predicts memory 

• These effects on heart rate cannot be explained by modulation of respiratory patterns 

• Synchrony is lower in patients with disorders of consciousness

Summary

Heart rate has natural fluctuations that are typically ascribed to autonomic function. Recent evidence suggests that conscious processing can affect the timing of the heartbeat. We hypothesized that heart rate is modulated by conscious processing and therefore dependent on attentional focus. To test this, we leverage the observation that neural processes synchronize between subjects by presenting an identical narrative stimulus. As predicted, we find significant inter-subject correlation of heart rate (ISC-HR) when subjects are presented with an auditory or audiovisual narrative. Consistent with our hypothesis, we find that ISC-HR is reduced when subjects are distracted from the narrative, and higher ISC-HR predicts better recall of the narrative. Finally, patients with disorders of consciousness have lower ISC-HR, as compared to healthy individuals. We conclude that heart rate fluctuations are partially driven by conscious processing, depend on attentional state, and may represent a simple metric to assess conscious state in unresponsive patients.