Yoga Sutras of Patanjali translated by Yogi Kalinath - Chapter 3, Verse 32
Pada 3, Sutra 32
By constraint on the light in the top of the head—vision of the perfected ones.
The ‘Perfected Ones’ are called Siddhas. They are spiritually accomplished beings and incarnate for the purpose of assisting the evolution of their fellow human beings.
It is possible to tune in to the energetic vibration of both incarnate and disincarnate Siddhas by focusing on the light that is generated inside the top of the skull. It is thought that this psychic light emanates from a very important gland called the pituitary gland. The pituitary gland is understood metaphorically to be a portal to the spiritual planes.
Ascending the internal planes with the Chakra system as a guide, Satya Loka is the highest plane where the concept of the Siddhas reside. The locus of constraint to en-vision the Siddhas are at the top of the head where the pituitary and pineal glands are located (where most would associate with the Third Eye / Ajna and Crown / Sahasrara Chakras—the visionary component being the stimulation and psychic awakening of the pituitary gland).
The Siddhis or Yogic Powers are a constraint of awareness on certain key loci vantage points to facilitate the expansion of consciousness with the specific aim to tap into the resources of the powers of the mind bridging the inner and outer, the above and below, the here and elsewhere.