Expert: John Locke - 2/18/2009

Question
Dear Mr.Locke,
I have read an article on the newspaper and it says that music would affect a
person's heartbeat. Though, I still don't get the concept. Can you please
explain how does music affect our heartbeat?

Mason

Answer
Thanks for using AllExperts. Your question actually gets to the heart of a fairly complex interaction between the environment and our conscious and unconscious reactions to it.

First, it's important to recognize that heart has intrinsic muscle contractility, meaning that it can beat by itself without any outside influence. Indeed, hearts cut out of animals will continue to beat at a steady rate for some time until the cells of the heart die from lack of nutrients. The body regulates the heart beat by increasing it or decreasing it, but it does not directly signal the heart to beat by itself. This activity is effectively beyond our conscious control; it is regulated by the autonomic nervous system, which is entirely unconscious; it is distinguished from the somatic nervous system that controls skeletal muscle, which is under our voluntary control. The autonomic nervous system controls other unconscious activities like digestive motility, the contraction and relaxation of blood vessels, sweating, and secretion of mucus. These are the kinds of activities that we don't want to spend time actively controlling.

There are two parts of the ANS with essentially opposite functions: the parasympathetic and sympathetic nervous systems. The parasympathetic causes changes in the body that support relaxation and energy conservation, like slowed heart beat, slower breathing, increased digestive system activity, and pupil constriction. The sympathetic nervous system gets the body ready for energy expenditure, typically in a stressful situation; it causes changes like increased heart rate, increased blood pressure, secretion of hormones that increase muscle tone, and so forth. The ANS is highly responsive to emotional states--you may have experienced the sensation of becoming upset and losing your appetite. That is the result of increased sympathetic nervous system activity due to your unhappy emotional state, with one of the effects of the SNS being to shut down the digestive system.

The effect of music on heart rate is another example of ANS activity. At the most basic level, people who hear music that they enjoy will feel happy and relaxed, which supports an increase in parasympathetic nervous system activity. This causes release of the neurotransmitter acetylcholine into the heart, which triggers a decrease in heart rate. Decreased heart rate is one manifestation of the overall increase in parasympathetic activity caused by the relaxed state of mind. Presumably, people who hear music that they do not enjoy will experience increased sympathetic nervous system activity, with the opposite effect.   

Now, this is a straightforward and attractive explanation, but the simple fact that it is self-consistent does not mean that it is true. Science requires evidence for the acceptance of any new idea, and it only by the collection of evidence that science can proceed. Many, many trials have been carried out on this question (not a few of which are done by high school students in science projects), with results varying from no effect to a dramatic decrease in heart rate. See here for an example with music played for patients before surgery:
http://www3.interscience.wiley.com/journal/118662227/abstract

Surprisingly, the methodology for these studies is often poor and it is hard to draw firm conclusions from the data collected. In short, playing music should affect heartbeat by inducing relaxation or stimulation, and it should do it by the mechanism described above, but the body of evidence is incomplete at this time on the subject.