Activation of Sympathetic Nervous System as a Biomarker for Deep Meditation

It has been reported that meditation is a progressive procedure to achieve a thoughtless and transcendental deep meditation state. However, it remains difficult to know whether and when the practitioner has achieved deep meditation state for lack of a reliable and objective measure. The aim of this study is to explore an electrophysiological biomarker for the deep meditation stage by studying the autonomic nervous system (ANS) activities during meditation using heart rate variability (HRV). We recruited 70 experienced Tibetan Buddhist monks, and recorded electrocardiogram signal for ~10 min of rest followed by ~30 min of meditation. We found two different stages of meditation, i.e., light meditation (0-10min) and deep meditation (after 10min) stages, which can be distinguished by the increased very low frequency (VLF, 0.003-0.04Hz) and low frequency (LF, 0.04-0.15Hz) power. The light meditation stage was comparable with the rest in the ANS activities, while the deep meditation stage was significantly different from the rest and light meditation stage. We speculate that the deep meditation stage could be marked by significant increases of VLF and LF. Meanwhile, ratio of low and high frequency power, standard deviation of RR intervals and fractal scaling exponents of detrended fluctuation analysis also increased in the deep meditation stage. Our results indicated that meditation is a dynamic process and the deep meditation was dominated by activated sympathetic nervous system.