At the forefront of the new science of the heart–brain connection has been recent research into heart rate variability (HRV), a measure of the nervous system’s flexibility for emotional self-regulation.
In the 1960s and 70s, researchers John and Beatrice Lacey established scientific evidence that the heart communicates to the brain in a way that affects how we perceive and react to the world (Lacey & Lacey, 1974). German research by Velden and Wölk in the 1980s found that cognitive performance and cortical function are under the influence of the heart by means of afferent (heart to brain) inputs on neurons in the thalamus that affect the global synchronization of cortical activity (Velden & Wölk, 1987; Wölk & Velden, 1989). Importantly, the researchers identified the pattern and stability of these afferent inputs, which in turn have global effects on brain function. The heart, it seems, wields more control over the brain than we had supposed. Since these early discoveries there has been a proliferation of studies on HRV as a marker for physical and emotional well-being.
Simply put, HRV measures the variability in time between heartbeats. This, it turns out, is a good gauge of the interplay between the autonomous nervous system (ANS) and the heart. The parasympathetic branch of the ANS, via the vagus nerve, connects to the heart’s pacemaker (the concentration of nerve cells in the sinoatrial node in the heart that initiates heart contractions) and exerts an inhibitory effect on heart rate. It is, as it were, the braking system for the heart. On release of the parasympathetic brake, the heart rate rises. This operation of the vagus nerve upon the heart’s pacemaker occurs on a moment-by-moment basis, resulting in slight variations of timing between heartbeats. High HRV indicates that the heart is readily and flexibly influenced by the vagal brake, and this, it has been discovered, is a good indicator of our emotional flexibility.
Lacey, B. C., & Lacey J. I. (1974). Studies of heart rate and other bodily processes in sensorimotor behavior. In P. A. Obrist, A. H. Black, J. Brener, & L. V. DiCara (Eds.), Cardiovascular psychophysiology (pp. 538–564). Chicago, IL: Aldine.
Velden, M., & Wölk, C. (1987). Depicting cardiac activity over real time: A proposal for standardization. Journal of Psychophysiology, 1, 173–175.
Wölk C., & Velden, M. (1989). Revision of the baroreceptor hypothesis on the basis of the new cardiac cycle effect. In N. W. Bond & D. A. T. Siddle (Eds.), Psychobiology: Issues and applications (pp. 371–379). Amsterdam, Netherlands: Elsevier.