The Science of Yoga

receptors for sex hormones, including testosterone. Scientists have shown that the stimulation of the amygdala results in a wide variety of sexual activities, including erection, ejaculation, ovulation, and the rhythmic movements of copulation. The stimulus can be purely hormonal. Dutch scientists recently studied middle-aged women whose amygdalas had undergone decline and found that small doses of testosterone could restore the organs to youthful vigor.
    As the scans let scientists peer deep, they began to see that fast breathing had different repercussions on different parts of the brain. The limbic system experienced no activity drops like those of the cortex. It moved to its ownbeat. Sex and hyperventilation could deprive the cerebral cortex of blood and oxygen, diminishing the higher functions of the brain, even as its inner regions kept going strong. It was like a late night in the suburbs. The residents turned out the lights upstairs while continuing to party in the basement.
    In Germany, Torsten Passie, a psychiatrist at the medical school of the University of Hannover, drew on the limbic findings to propose a theory of sex hyperventilation. The decrease in cortical management, he wrote, resulted in a “more primitive mode of brain functioning” marked by heightened emotions, declines in self-control, and a deepening sexual trance.
    All of which led to an intriguing question. Could fast breathing from yoga or anything else produce a sexual high in and of itself? The question went to knotty issues of causation. Was fast breathing solely a result of sexual stimulation, or could it also work as an initiator?
    In Vancouver, Lori A. Brotto and other sex researchers at the University of British Columbia began looking for answers. The scientists recruited twenty-five women—all heterosexual and sexually experienced—and measured their responses to an erotic film. The reactions were noted twice, once after hyperventilation and on a different day without the benefit of fast breathing. The women took thirty deep breaths per minute for two minutes. By the standards of Bhastrika and other kinds of rapid yogic breathing, the routine was fairly mild. Even so, the researchers judged that the breathing produced a state of sympathetic dominance that lasted at least seven minutes.
    Their report, published in 2002, showed that the women watching the film experienced a significant rise in the amplitude of their vaginal pulses, suggesting that viewing the amorous film did in fact produce genital arousal. As a group, the amplitude doubled.
    That led to an investigation of whether the breathing technique could have practical applications. Brotto and her colleagues recruited sixty women with sexual arousal disorder, or SAD, and a control group of forty-two women with healthy sex lives. Again, the volunteers were all heterosexual and sexually experienced. The women saw two erotic films in a row. One group hyperventilated before the first film, and then had a resting period before viewing the second. The procedure with the second group was reversed, so fast breathing took place before the second film.
    The results suggested thateven short periods of fast breathing could improve arousal. As before, the healthy women responded more vigorously to the erotic film if they hyperventilated in advance. But so did the SAD women. Their histories included the absence of or diminished ability to respond to physical stimulation of the genitals as well as to visual and auditory cues that normally result in aroused feelings. In many respects, these women were difficult cases. Yet their levels of excitement were almost as high as those of their peers.
    In short, the evidence suggested that hyperventilation could promote arousal not only in healthy women but among those with diminished libidos.
    Fast breathing fanned the flames.
    My first visit to a Bikram studio drove home the primal nature of yoga breathing. I had done yoga for decades. But now, in my new frame of mind, I realized that most classes were structured—by accident or design—to echo one of the most basic of all human experiences.
    It was a full house that night, the mirrored room packed with men and women, most in great shape and apparently enthusiasts who practiced a lot. A man up front kept a big jug of water next to him. He clearly understood better than I how hot yoga could produce torrents of sweat and the urgent need for liquid refreshment (a situation not unknown in adult