afferent signals in physiological regulation, our earlierdiscussion also illuminates the hearts significant influence on perceptual and cognitive functionvia its input to higher brain centers. Our discussion has thus far covered behavioral data showinga relationship between the hearts input and cognitive performance, as well aselectrophysiological studies demonstrating the synchronization of brain activity to the heart.Beyond these findings, there is also a considerable body of other electrophysiological evidencedemonstrating the modulation of higher brain activity by cardiovascular afferent input (see Lacey& Lacey, 1970; McCraty, 2003; and Sandman et al., 1982, for reviews).Experiments carried out in Germany by psychophysiologist Rainer Schandry havedemonstrated that afferent input from the heart evokes cortical responses analogous to classicalsensory event-related potentials. These experiments have shown that afferent input from thecardiovascular system is accompanied by specific changes in the brains electrical activity.Schandry and colleagues found, as have we, that this activity is most pronounced at thefrontocortical areas, a region particularly involved in the processing of visceral afferentinformation. In addition, psychological factors such as attention to cardiac sensations, perceptualsensitivity, and motivation have been found to modulate cortical heartbeat evoked potentials in afashion analogous to the cortical processing of external stimuli (Lader & Mathews, 1970;Montoya, Schandry, & Muller, 1993; Schandry & Montoya, 1996; Schandry, Sparrer, &Weitkunat, 1986). In our own study, in which we investigated the electrophysiology ofinformation processing in relation to intuition, we also found that the hearts afferent inputsignificantly modulates frontocortical activity, especially during the psychophysiologicalcoherence mode (McCraty et al., 2004a, 2004b).The observation that the hearts afferent input modulates frontal activity is concordant withother findings that activity in the prefrontal cortex covaries with changes in the heart rhythm(Lane et al., 2001). This is consistent with the biological principle of reciprocal connections inneural systems. Therefore, in addition to the well-established routes (e.g., the thalamic pathway)by which cardiovascular afferent signals modulate higher cortical function, there may well beadditional routes from the heart to the prefrontal cortex.Biochemical InteractionsIn addition to its extensive neurological interactions with the brain and body, the heart alsocommunicates with the brain and body biochemically, by way of the hormones it produces.Although not typically thought of as an endocrine gland, the heart in fact manufactures andsecretes a number of hormones and neurotransmitters that have a wide-ranging impact on bodyas a whole.The heart was reclassified as part of the hormonal system in 1983, when a new hormoneproduced and secreted by the atria of the heart was discovered. This hormone has been variouslyINTEGRAL REVIEWDecember 2009Vol. 5, No. 2termed atrial natriuretic factor (ANF), atrial natriuretic peptide (ANP), or atrial peptide.Nicknamed the balance hormone, and playing an important role in fluid and electrolytehomeostasis, it exerts its effects on the blood vessels, kidneys, adrenal glands, and many of theregulatory regions of the brain (Cantin & Genest, 1985, 1986). In addition, studies indicate thatatrial peptide inhibits the release of stress hormones (Strohle, Kellner, Holsboer, & Wiedemann,1998), reduces sympathetic outflow (Butler, Senn, & Floras, 1994), plays a part in hormonalpathways that stimulate the function and growth of reproductive organs (Kentsch, Lawrenz, Ball,Gerzer, & Muller-Esch, 1992), and may even interact with the immune system (Vollmar, Lang,Hanze, & Schulz, 1990). Even