it is essentially oscillating at its resonant frequency; this is reflected in thedistinctive high-amplitude peak in the HRV power spectrum around 0.1 Hz. Most mathematicalmodels show that the resonant frequency of the human cardiovascular system is determined bythe feedback loops between the heart and brain (Baselli et al., 1994; DeBoer, Karemaker, &Strackee, 1987). In humans and in many animals, the resonant frequency of the system isapproximately 0.1 Hz, which is equivalent to a 10-second rhythm. The system naturallyoscillates at its resonant frequency when an individual is actively feeling a sustained positiveemotion such as appreciation, compassion, or love, (McCraty et al., 1995) although resonancecan also emerge during states of deep sleep.Furthermore, increased heartbrain synchronization is observed during coherence;specifically, the brains alpha rhythms exhibit increased synchronization with the heartbeat inthis mode. This finding is discussed in greater depth in Appendix D.Finally, there tends to be increased cross-coherence or entrainment among the rhythmicpatterns of activity generated by different physiological oscillatory systems. Entrainment occurswhen the frequency difference between the oscillations of two or more nonlinear systems dropsto zero by being frequency pulled to the frequency of the dominant system. As the bodys mostpowerful rhythmic oscillator, the heart can pull other resonant physiological systems intoentrainment with it. During the psychophysiological coherence mode, entrainment is typicallyobserved between heart rhythms, respiratory rhythms, and blood pressure oscillations; however,other biological oscillators, including very low frequency brain rhythms, craniosacral rhythms,and electrical potentials measured across the skin, can also become entrained (Bradley &Pribram, 1998; Tiller et al., 1996).Figure 3 shows an example of entrainment occurring during psychophysiological coherence.The graphs plot an individuals heart rhythm, arterial pulse transit time (a measure of beat-to-beat blood pressure) (Bradley & Pribram, 1998), and respiration rate over a 10-minute period. Inthis example, after a 300-second normal resting baseline period the subject used a heart-basedpositive emotion refocusing technique known as Freeze-Frame, (Childre & Martin, 1999) whichSpectral analysis decomposes the HRV waveform into its individual frequency components andquantifies them in terms of their relative intensity using power spectral density (PSD) analysis. Spectralanalysis thus provides a means to quantify the relative activity of the different physiological influences onHRV, which are represented by the individual oscillatory components that make up the heart rhythm.INTEGRAL REVIEWDecember 2009Vol. 5, No. 2involves focusing attention in the area of the heart while self-generating a sincere positiveemotion, such as appreciation. After the subject used the Freeze-Frame technique, the threerhythms shifted from an erratic to a sine-wave-like pattern (indicative of the coherence mode)and all entrained at a frequency of 0.12 Hz. (Tiller et al., 1996). The entrainment phenomenon isthus an example of a psychophysiological state in which there is increased coherence within eachsystem (autocoherence) and among multiple oscillating systems (cross-coherence) as well. Thisexample also illustrates how the intentional generation of a self-regulated positive emotionalstate can bring about a phase-shift in physiological activity, driving the physiological systemsinto a globally coherent mode of function.120180240300360TIME (SECONDS)2520151008.00E-56.00E-54.00E-52.00E-50.00E+00.80.60.40.2420480540600500.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4FREQUENCY00.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4FREQUENCYFigure 3. Entrainment. The top graphs show an individuals heart rate variability, pulse transittime, and respiration rhythms over a 10-minute period. At the