Kundalini.Tantra.by.Satyananda.Saraswati

a white drop, which is the nectar dripping down to vishuddhi chakra. It is the ultimate
source out of which all things manifest and into which all things return.
"......(bindu) is the cause of the creation of word and meaning, now entering and now
separating from one another."
".....from that (bindu) came ether, air, fire, water, earth and the letters of the alphabet."
Kama-Kala-Vilasa (verses 6-9)
Bindu visarga is interconnected with vishuddhi chakra in the same way that the minor
centers of the digestive system are connected with manipura, and those of the uro-genital
and reproductive systems with swadhisthana and mooladhara chakras. Similarly, the
minor centers of the respiratory and circulatory systems are integrated into anahata
chakra and so on. In each case, the connection is mediated by the particular group of
nerves associated with that chakra. Bindu and vishuddhi are connected via the network of
nerves which flow through the interior portion of the nasal orifice, passing through lalana
chakra, which is found at the uvula or palate. Therefore, when awakening takes place in
vishuddhi, it simultaneously takes place in bindu and lalana.
The ten paired cranial nerves which emerge along the brain stem from their
associated centers or nuclei, are considered to actually have their initial origins within
this tiny center, so that the whole visual, nasal, auditory and tasting systems are
ultimately manifestations from bindu.
The location point
The seat of bindu is at the top back of the head, exactly at the spot where the Hindu
brahmins leave a tuft of hair growing. Although this custom is still being followed today,
its original purpose has been completely forgotten. In Sanskrit that tuft of hair is called
shikha, which means 'the flame of fire'. Here, the word 'flame' stands for the flame of
vasanas or the hidden karmas belonging to the previous life.
During the period of sandhya, when the child underwent the thread ceremony and
was initiated into mantra, they used to hold and tighten this tuft as much as possible and
then tie it. When the tuft was tightened and the child practised mantra, he developed a
powerful and continuing awareness of this bindu point alone. He felt tightness rather than
pain at that point. This is one traditional way to gain contact with bindu visarga.
Tantric physiology
According to tantric tradition, within the higher centers of the upper cortex of the
brain there is a small depression or pit which contains a minute secretion. In the center of
that tiny secretion is a small elevation or point like an island in the middle of a lake. In
the psychophysiological framework, this tiny point is considered to be bindu visarga.