relations between the different brain rhythms found in the EEG and themany different aspects of cognition.13 For example, the alpha rhythm amplitude is lower duringmental calculations while the beta rhythms increase (Nunez, 2000).Recent research has focused on the global organization of cooperative workings of local andregional cell groups in order to better understand the brains dynamic complexity. At anoperational level, coherence in this context is a specific quantitative measure of functionalrelations between paired locations. In general, this research has shown that separate regions inthe brain can exhibit high coherence in specific frequency bands and, at the same time, lowcoherence in other bands. The resulting correlated activity between these brain regions is cross-coherence, which is thought to emerge either from direct neural connections between the regions,common input from the thalamus and other neocortical regions, or both (Nunez, 2000).However, cross-coherence also occurs between distant cortical structures that are not necessarilyinterconnected anatomically (Bressler, Coppola, & Nakamura, 1993). This raises the question ofwhat other mechanisms might account for this communication among distant brain regions.A notable example of such cross-coherence has been described by Rodolfo Llinas, Chief ofPhysiology and Neuroscience at the New York University School of Medicine. He observed thatspecific areas of the cortex emit a steady oscillation, at a frequency of around 40 cycles persecond (40 Hz). He also found that remote areas of the cortex were phase-locked at this 40-Hzfrequency, meaning that the waves they produced all oscillated in synchrony. This led Llinas andothers to suggest that the neurons perform in synchrony because they follow a kind of conductor(Ratey, 2001).The prime candidate for the brains internal conductor is the many intralaminar nuclei, locatedwithin the thalamus. These nuclei receive and project long axons to many areas of the brain.They take in information, reply to it, and monitor the responses to their replies, thus creatingelaborate feedback loops in which resonant activity (~40 Hz) is modified by incoming sensoryinput. If the intralaminar nuclei are damaged, the person enters a deep and irreversible coma.Indeed, it appears that it is only when the conductor synchronizes the brains activity that webecome conscious. When this happens with a sufficient number of neural networks, theoscillations become ordered and globally coherent. As they spread their influence, recruitingmore networks to join them, consciousness arises (Ratey, 2001).The thalamus appears to play an active role in the generation of all the global EEG rhythms,and it should be emphasized that phase synchrony has been shown to occur in all the frequencyThe main rhythms that have been identified are: the delta rhythm (04 Hz), the theta rhythm (4-8 Hz),the alpha rhythm (8-12 Hz), the beta rhythm (12-16 Hz), and most recently the gamma rhythm (~ 40 Hz).INTEGRAL REVIEWDecember 2009Vol. 5, No. 2bands found in the EEG, not just in the 40 Hz band. 14 For example, different types ofsynchronization occur in the alpha band during the different phases of memory processes(encoding and retrieval) (Fingelkurts, Krause, Kaplan, Borisov, & Sams, 2003), and cross-coherence increases in the theta band during mental calculations (Nunez, 2000). Coherence inthe alpha band is also correlated to perceptual and decision-making processes, and it increases inthe