Not Tao:
Not sure about most of this, but the whole concept of the pineal gland relating to the third eye is just folk science (i.e. made up). The pineal gland is mostly responsible for our sensitivity to day/night light levels and is linked to dreaming and the activation related hallucination caused by drugs (which is a kind of dream state). There was some philosopher in the 1700's who thought the pineal gland was the link to the soul, and ever since then it's been mischaracterized a lot of different ways. The link to DMT reignited a lot of speculation about it and now you see new age articles everywhere talking about decalcifying your pineal gland and opening the third eye chakra - all of which is based on nothing in particular.
Descartes. And Blavatsky. In fact Blavatsky has been incredibly successful in stuffing people's heads with stupidity. In fact if there was a Nobel for baloney Blavatsky would be a three time winner. I read a lot of theosophy a long time ago but it would have been better to read physiology.
http://plato.stanford.edu/entries/pineal-gland/#3.3The DMT one is a real possibility, though they only found it in rat brains so far, which doesn't stop people going on about DMT from the human pineal.
So anyway I'm no closer to knowing what that energy centre is, after looking through anatomy websites. There are various veins, membranes, nerves and sinus cavities in the area - but one thing we can't feel is the brain or pineal gland directly.
But the pineal has interesting properties anyway so it could play a role in meditation.
https://en.wikipedia.org/wiki/Pinealocyte
Has there been a meditator who has had the gland removed - cancer or whatever ?