For a 2014 study in the Journal of Neuroscience, University of Sussex psychologist Sarah Garfinkel and her colleagues set out to determine how much our heartbeats influence our emotions. They had participants watch pictures flash in front of them, and asked them to identify when they spotted a face. Some faces looked fearful, others looked happy or disgusted, and others wore a neutral expression. The participants didn't know it, but the researchers had timed the pictures to appear during certain points during their heartbeat: some flashed during the systole, contraction phase of their heartbeat; others flashed during the diastole, or relaxation phase. The team found that people detected the fearful faces more easily and rated them as more intense when they appeared during the systole phase. They performed a similar study while scanning participants' brains in an MRI and found that seeing fearful faces during systole phase was linked with more activity in the hippocampus and amygdala—areas associated with fear.
We often think that the brain rules the body, but the body is much more complex than that. Learn more about the mind-body connection in the videos below.