The Heart: How Does It Respond to Fear?

Illustration: cacaroot/Thinkstock

Experts believe that the human body feels fear in both, heart and head.

The brain is the control center of our body; it manages all our body functions, responses, and, emotions. A particular stimulus compels us to respond accordingly.

The information passed by internal organs to the brain does not only affect the physiological responses. We do not know what is going on in our internal body processes but they can affect our perception.

Decades ago, it was suggested that it is not the external stimuli that trigger the fight or flight responses. Rather, the increased heart rate and accelerated breathing result in emotions like fear. Since then, many examples demonstrated that mental functions change by physiological stimuli.

Functioning of Heart

Many types of research show that one complete heartbeat has two phases. The systolic phase is responsible for contraction of the heart and distribution of blood whereas diastole occurs when the heart relaxes and fills the blood.

In a new study, Esra Al and colleagues discovered that during systole, our brain works to minimize the physical changes resulting from the pulse so that they cannot be mistakenly recognized as an external stimulus. This prevents the constant disturbances that the pulse would cause.

This is mainly because during systole our inhibitory parts of our brain receive signals about our heart activity. However, in doing so, several low-intensity stimuli, which coincide with the systole, remain undetected.

For the study, the National Academy of Sciences analyzed thirty-seven people by exposing them to weak electrical stimuli. The stimulus was mostly detectable during the diastole and missed during systole.

Also Read: A New Technology Increases Hope For An Implantable Artificial Kidney

Esra Al, the author of the research, considered it very surprising how perception by human brain changes in milliseconds of a heartbeat. The study also reported that people who are more sensitive towards their heartbeat show less response to the external stimuli. This means that the increased sensitivity to the internal stimuli distracts the person to concentrate on the external stimulus.


Many studies have shown that perception declines during the systolic phase. A study by Garfinkel and colleagues recorded that words shown to a person at the diastole are recognized and retained easily. The decrease in memory for words at systole was even greater than those with low confidence.

We come to know that various somatosensory detections reduce during the systolic phase of the heart cycle. But during systole, the feeling of fear doesn’t end.

Amygdala is the part of the brain which processes several emotions including fear and anxiety. Unlike other stimuli, threatening stimuli are not suppressed during the systolic phase of the cardiac cycle, found the study.

Instead, in addition to activating the inhibitory regions, the amygdala also becomes active during the systole resulting in greater fear perception.

Garfinkel and her team discovered that the perception of fearful faces by the people is enhanced at systole and repressed at the diastole. Moreover, the intensity rating of the fearful faces reflected the same pattern as higher at systole.

It means that the perception and intensity of fear increase when our heart makes a heartbeat. Fear perception in anxious people does not change by the timing of the heartbeat. This proves that the heart-brain pathway somehow faces disruption in anxious individuals.

Therefore, they cannot use the cardiac timing to reduce fear. Hence, high fear perceptions cause anxiety disorders. The improved fear perception at the systole, when other somatosensory stimuli are suppressed, helps us respond in a better way.

The experts say that when in fear, a person doesn’t want to perceive pain and can run over broken glass and other objects to avoid the threat. Such a person becomes extra sensitive to the threatening stimulus than to pain.

Adeena Tariq Lari
The author is a graduate of dental surgery from the Dow University Health Sciences, Karachi. She has an academic background in content writing as well as English literature, giving her an edge in the field. Adeena is always curious about physical and mental health. She is always passionate about research and delivering high-quality reliable content to users.