Our heart doesn't beat at a constant frequency. What can this tell you about your brain state and multitasking performance?
People take for granted that our heart beats at a constant frequency, but this is not true. So, if the number of contractions of our heart per minute is 60, this does not mean that we have a regular beat every second. It varies between 0,9 sec and 1,2 sec. This introduces the concept of heart rate variability (HRV) which refers to the physiological phenomenon of variation in the time interval between heartbeats. HRV is controlled by the balance between parasympathetic and sympathetic nervous system. The parasympathetic system supports a “relaxed” mode and is active when the resting and digesting response is engaged, whereas the sympathetic system supports a “survival” mode and is active when the fight or flight response is engaged. When the parasympathetic system is dominant, HRV increases; whereas when the sympathetic system takes over, HRV decreases.
So, put it simple: HRV is a proxy of parasympathetic control and represents a measurement of our current preparedness to cope with all varieties of stress: physical, mental and emotional. That is, the higher HRV, the healthier we are!
What is the connection between brain and heart? The seminal neurovisceral integration model by Julian Thayer tries to answer this question. This model suggests that the prefrontal cortex regulates activity in limbic structures which act to inhibit parasympathetic activity and activate sympathetic circuits. HRV arises from the variation in the output of these two branches of the autonomic system and, following a multidirectional process, activity in the prefrontal cortex can hence modulate HRV. If this is true, it means that HRV can predict performance in cognitive functions related to the prefrontal cortex, such as mental flexibility.
Laura Steenbergen and I were interested in exploring that idea and we did so by looking at individual differences in HRV and multitasking performance, because multitasking has been found to be related to activity in the prefrontal cortex. Multitasking is something we master on a daily basis, for example when we are cooking a meal and at the same time talking on the phone. It involves doing two tasks at the same time or very quickly after one another. If better HRV is indeed related to optimal activity of the prefrontal cortex, does this mean people with high HRV are better in multitasking?
That is indeed what we found when having people perform a multitasking experiment where, on a computer screen, they have to react to visual and auditory stimuli in rapid succession. As expected people with high HRV were the ones who were better in executing two tasks at the same time. So, it seems to be true that a variable heart rate and a multitasking mind go hand in hand.
If you want to read more about our study on HRV and multitasking, make sure to check out our recently published article!
Colzato, L. S., & Steenbergen, L. (2017). High vagally mediated resting-state heart rate variability is associated with superior action cascading. Neuropsychologia, 106, 1-6.