The first phase—Neural switch:
The NRT covers the back(dorsal), sides (lateral), and bottom (ventral) nuclei of the thalamus—where sensory and motor inputs pass through the thalamus to the cortex. However, thalamic nuclei that modulate alertness levels are not covered by the NRT: the intralaminar nuclei ( governs how “bright the light is” or general wakefulness level. It is the extension of the reticular activation system in the brain stem); anterior nuclei (part of the limbic-cingulate circuit that is part of the emotion loop) >medial dorsal nucleus (feedback loop with frontal cortices to maintain level of wakefulness in executive frontal processing areas); and centromedian (feedback loop with frontal and basal ganglia).
The EEG signature of this process is global alpha power and high EEG coherence (Travis, International Journal of Psychophysiology, 2001). The EEG signature changes within one or two seconds of beginning a 20-minute TM session. It is like flipping a “neural switch.” Other researches suggest that TM involves successive orienting/habituation cycles overtime (Arenander, 1997, Tucson conference). If this were the case, (1) the changes in EEG and physiology would gradually change rather than emerge very quickly (about one second), (2) you would expect to see the EEG of orienting, whichis decreased alpha EEG. Since these are not seen, if seems that the “neural switch” model better explains the beginning of TM.
The second phase: Effortless maintenance of the state of restful alertness resulting from the first phase of TM.
Those thalamic nuclei that are not covered by the NRT (intralaminar nuclei, anterior nuclei, medial dorsal nucleus, and the centromedian) can continue in their function—to maintain alertness levels in the absence of specific content. These are self-referral circuits—the cortex signals the thalamus, and the thalamus echoes back. These feedbackloops may maintain the state of restful alertness during TM practice.
TM practice exercises these “restful alert” circuits through use. Over time, these circuits may become self-sustaining, so that they can continue in their self-referral “murmuring” even as content comes through the thalamus, up to the cortex, and into consciousness awareness. Then self awareness, alertness, Being, co-exist with ever-changing experience. Outer activity is experienced on the ground of inner unboundedness and silence. This is the state of enlightenment. (See Travis et al, Biological Psychology, 2002).