Travis, F.T. & Wallace R.K. (1999). EEG and Autonomic Patterns during Eyes-Closed Rest and Transcendental Meditation Practice: The Basis for a Neural Model of TM practice. Consciousness and Cognition, 8, 302-318.

Abstract
In this single-blind within-subject study, autonomic and EEG variables were compared during 10-minute, order-balanced eyes-closed rest and Transcendental Meditation (TM) sessions. TM sessions was distinguished by (1) lower breath rates, (2) lower skin conductance levels, (3) higher respiratory sinus arrhythmia levels, and (4) higher alpha anterior-posterior and frontal EEG coherence. Alpha power was not significantly different between conditions. These results were seen in the first minute and were maintained throughout the 10-minute sessions. TM practice appears to (1) lead to a state fundamentally different than eyes-closed rest; (2) result in a cascade of events in the central and autonomic nervous systems leading to a rapid change in state (within a minute) that was maintained throughout the TM session; and (3) be best distinguished from other conditions through autonomic and EEG alpha coherence patterns rather than alpha power. Two neural networks are suggested that may mediate these effects. The rapid shift in physiological functioning within the first minute might be mediated by a "neural switch" in prefrontal areas inhibiting activity in specific and non-specific thalamo-cortical circuits. The resulting "restfully alert" state might be sustained by a basal ganglia/corticothalamic threshold regulation mechanism automatically maintaining lower levels of cortical excitability.