afferent signals on the brain, the hearts rhythmic pattern over longer timescales must also be considered as an important factor in itself, in addition to those of stimulusintensity, heart rate, and pressure. As we have seen, it is likely that the macro-scale pattern of thehearts activity may have a much greater effect on performance than the within-cardiac cycleeffects.Afferent Input to Brain Centers other than the ThalamusAnother important consideration, in relation to heartbrain interactions, is that while themicro-pattern model focuses solely on cardiovascular input to the thalamus, there are otherINTEGRAL REVIEWDecember 2009Vol. 5, No. 2neural pathways by which the hearts input can modulate cortical activity and thus performance.As shown in Figure 5, cardiovascular inputs from the vagal afferent nerves first reach the nucleusof tractus solitarius (NTS) and from there travel directly to the parabrachial complex,periacqueductal grey, thalamus, hypothalamus, and amygdala. There are then connections bywhich the afferent inputs move from the amygdala, hypothalamus, and thalamus to the cerebralcortex. There is also evidence to suggest the existence of afferent pathways from the medulladirectly to the prefrontal cortex (McCraty et al., 2004b).Although this diagram primarily shows the afferent pathwaysone-way flow of input to thebrainin most cases the regions are reciprocally interconnected such that information flows inboth directions. This reciprocally interconnected network allows for continuous positive andnegative feedback interactions and the integration of autonomic responses with the processing ofperceptual and sensory information. In addition, the numerous distributed parallel pathwayspermit multiple avenues to process a given response.HeartBrain SynchronizationThe third way in which the picture is more complicated is that whereas Wolk and Veldenshypothesis considers only the alpha rhythm, there are other brain rhythms that are alsosynchronized to the heart. These include the beta rhythm as well as lower frequency brainactivity. Thus, it is likely that the effects of macro-scale cardiovascular dynamics on otheraspects of brain activity are also important in contributing to larger fluctuations in performance,such as those observed in the studies reported here.Appendix D presents evidence from a number of studies confirming that a significant amountof alpha rhythm activity is indeed synchronized to the activity of the heart. We have alsopresented additional evidence showing that Wolk and Veldens contention appears to have anempirical basis, in that we found that the alpha rhythm is synchronized to the cardiac cycle.Moreover, our evidence suggests that alpha synchronization increases duringpsychophysiological coherence and that other brain rhythmsnamely, the beta rhythm andlower frequency brain activityalso appear to be synchronized to the cardiac cycle.System Dynamics: Centrality of the Heart in thePsychophysiological NetworkTo this point our concern has been describing the nature, organization, and measurement ofsix different psychophysiological modes. In particular we have focused on thepsychophysiological coherence mode and its impact on various aspects of psychophysiologicalfunction, including pain perception, respiration, emotional processing, and cognitiveperformance. Now we turn to the basic question of system dynamics: how the heart, as the mostpowerful generator of rhythmic information patterns in the body, acts effectively to bind andsynchronize the entire system. This helps explain the mechanisms that underlie the hearts role inthe generation of system-wide coherence in the body as a whole. In addition to an overview ofresearch in