It is really a question of how far we carry the neurobiology/prana relationship. Neurobiologically speaking, sexual essences are the source of ecstatic conductivity (kundalini), and the purification of the nervous system through an effective integration of yoga practices provides the opening for the process to move forward, yielding the spiritual experiences. As we know, the stand-alone performance of mechanical vajroli (from the Hatha Yoga Pradipika) by men is not effective for expanding sexual function, and is just as likely to lead to unhealthy diversions in sex. This is why mechanical vajroli is not recommended in the AYP writings. It has been found that the daily sitting practices in the main lessons (deep meditation, spinal breathing, etc.) and the sexual methods in these tantra lessons (holdback, blocking, etc.) are more than enough to get the job done.

I am not saying that the physical/spiritual connection between whole body ecstasy and natural vajroli is absolutely how it is, going all the way in to the the most refined levels of divine ecstasy, but there is strong evidence that the connection between the neurobiology and spiritual experiences goes pretty far. The emergence of soma, amrita and ojas can be seen to be subdivisions of this, very refined substances finding their origin in the neurobiology of digestion (soma), brain functioning (amrita) and radiating outward in all directions through the entire nervous system (ojas). And you are right -- the presence of these substances is also evidence of natural vajroli, as is whole body mudra and other indicators of ecstatic bliss permeating the body and beyond.

Whether the neurobiology model of enlightenment turns out to be true in the long run is the question, isn't it? By taking this approach, many are given a handle on their experiences in terms of understanding the symptoms and underlying neurobiological changes that are clearly occurring. I have been asked hundreds of times in private, "Why is my spiritual ecstasy accompanied by sexual arousal?" The rise of natural vajroli is the reason. It is a key component of kundalini awakening.

Putting the neurobiology out in front also hangs a big carrot out there for modern science to grab on to. There are plenty of things here that can be measured, and sooner or later science will get around to it. As many more practitioners come forward having these experiences (inevitable now), and the general lay of the land of the enlightenment process becomes more familiar everywhere, a fertile new field for scientific research will emerge.

Those who are more mystically inclined can ignore all the neurobiology and simply enjoy the ride.

Either way, our bhakti (spiritual desire) and the maintenance of an effective daily practice routine will continue to be the engine for human spiritual transformation in ourselves, and in the population at large.

Onward!