Catherine de Lange, contributor
A few weeks ago I was walking home when I was followed by some men in a car. Feeling threatened I ducked behind a wall, and watched as they passed by slowly trying to find where I had gone. It wasn't until they drove off that I realised how fast my heart was pounding in my chest.
Of course, my body's reaction to the situation is unsurprising - the heart's incredible adaptability to mental triggers is an everyday occurrence.
Sensing a threat, my heart sped up, priming me to fight or run (or in this case, hide).
It now seems this long held understanding might just be part of the story, however, as new research is beginning to emerge suggesting that our hearts themselves might be responsible for the extent to which we experience fear, rather than merely reacting to scary stimuli.
The idea is an extension of what is known as embodied cognition?- that our bodies can drive our thoughts. Good examples of the concept come from studies showing that people asked to do a task in a slouching position felt less proud and in a worse mood than those sitting up straight, said Sarah Garfinkel, a psychologist at the University of Sussex, speaking at the Association for the Scientific Study of Consciousness conference in Brighton, UK, last week.
Garfinkel's own research is focused on this interplay between physiology and emotion, more specifically whether the cardiac cycle affects our emotional response to scary stimuli.
In one experiment, the results of which were presented at the conference, she asked people to look at a stream of flashing images and highlight when they spotted a face. Some of the faces looked fearful, others looked neutral.
Unbeknown to the volunteers, Garfinkel time-locked the images to appear in sync with their heart-beat. Sometimes the images were synced with the systole phase - the part of the cardiac cycle where the heart muscle contracts to squeeze blood out of the heart, at other times they were linked to the diastole phase - the stage where the heart relaxes and fills after contracting.
Garfinkel found that people were better at spotting fearful faces compared with neutral faces, but only when the pictures were timed to appear at the systole phase.
In another study, in which volunteers saw the same pictures while having their brain scanned using MRI, she found that people had a stronger response in the hippocampus and amygdala - areas of the brain associated with fear - when they were shown fearful faces at systole than when they saw them at diastole. In other words, half a heartbeat was all it took for a person to experience a significantly different response to the same scary stimulus.
The finding seems to be mediated by barorecepors - stretch and pressure sensitive receptors in the heart and surrounding arteries which help initiate systole. "When barroreceptors are activated at systole, a flurry of activity is transferred to the brain at that moment," Garfinkel says, which could explain the difference in the brain scans.
This then begs the question: why this should happen? The effect could simply be a by-product of the neural effects of the heart telling the brain it needs to contract during systole. But Garfinkel believes otherwise - instead she thinks the difference must be some form of functional adaptation. The findings also chime with other experiments presented at the conference which show how the heartbeat can mediate other emotional traits, such as empathy.
Which all goes to show there might be some truth in the old adage: listen to your heart.
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