research on the physiological correlates of positive emotions we have found that whencertain positive emotional states, such as appreciation, compassion, or love, are intentionallymaintained, coherent heart rhythm patterns can be sustained for longer periods, which also leadsto increased synchronization and entrainment between multiple bodily systems. Because it ischaracterized by distinctive psychological and behavioral correlates as well as by specificpatterns of physiological activity throughout the body, we introduced the termpsychophysiological coherence5 to describe this mode of functioning.In earlier publications (Tiller et al., 1996), the psychophysiological coherence mode was referred to asthe entrainment mode because a number of physiological systems entrain with the heart rhythm in thismode.INTEGRAL REVIEWDecember 2009Vol. 5, No. 2The development of heart rhythm coherencea stable, sine-wave-like pattern in the heart ratevariability waveformis the key marker of the psychophysiological coherence mode. Heartrhythm coherence is reflected in the HRV power spectrum as a large increase in power in the lowfrequency (LF) band (typically around 0.1 Hz) and a decrease in the power in the very lowfrequency (VLF) and high frequency (HF) bands. A coherent heart rhythm can therefore bedefined as a relatively harmonic (sine-wave-like) signal with a very narrow, high-amplitude peakin the LF region of the HRV power spectrum and no major peaks in the VLF or HF regions.Coherence thus approximates the LF/(VLF + HF) ratio. (See Appendix A for an explanation ofthe HRV power spectrum and a description of the physiological significance of the differentfrequency bands.)A method of quantifying heart rhythm coherence is shown in Figure 2. First, the maximumpeak is identified in the 0.040.26 Hz range (the frequency range within which coherence andentrainment can occur). The peak power is then determined by calculating the integral in awindow 0.030 Hz wide, centered on the highest peak in that region. The total power of the entirespectrum is then calculated. The coherence ratio is formulated as:(Peak Power / (Total Power Peak Power)) (Childre & Martin, 1999)This method provides an accurate measure of coherence that allows for the nonlinear nature ofthe HRV waveform over time.Figure 2. Heart rhythm coherence ratio calculation.At the physiological level, psychophysiological coherence embraces several relatedphenomenaautocoherence, entrainment, synchronization, and resonancewhich areassociated with increased order, efficiency, and harmony in the functioning of the bodyssystems. As described above, this mode is associated with increased coherence in the heartsINTEGRAL REVIEWDecember 2009Vol. 5, No. 2rhythmic activity (autocoherence), which reflects increased ANS synchronization and manifestsas a sine-wave-like heart rhythm pattern oscillating at a frequency of approximately 0.1 Hz.Thus, in this mode the HRV power spectrum6 is dominated by a narrow-band, high-amplitudepeak near the center of the low frequency band (see Figures 3 below and 8 in Appendix A)(McCraty et al., 1995; Tiller et al., 1996).Another physiological correlate of the coherence mode is the phenomenon of resonance. Inphysics, resonance refers to a phenomenon whereby an unusually large oscillation is produced inresponse to a stimulus whose frequency is the same as, or nearly the same as, the naturalvibratory frequency of the system. The frequency of the vibration produced in such a state isdefined as the resonant frequency of the system. When the cardiovascular system is operating inthe coherence mode,