Psychosom Med. 1982 May;44(2):133-53.
By observing people meditating, the authors found that breath suspension (or pauses in breathing) coincided with periods of thoughtless awareness:
We observed, over four independent experiments, 565 criterion-meeting episodes of breath suspension in 40 subjects practicing the Transcendental Meditation technique (TM), a simple mental technique involving no breath control procedures. . . . Many TM subjects report experience of a completely quiescent mental state characterized by maintained awareness in the absence of thought. Eleven TM subjects were instructed to press an event mark button after each episode of this pure consciousness experience. The temporal distribution of button presses was significantly related (p less than 10(-10) to the distribution of breath suspension episodes, indicating that breath suspension is a physiological correlate of some, but not all, episodes of the pure consciousness experience.
(This post is not an endorsement of Transcendental Meditation, which is one of many techniques that involve breath suspension and not one I use. But Farrow and Hebert’s finding is consistent with my own experience.)
The Monkey Who Meditates 