Nyasavidya in Hindu religion is the performance of nyasa in religious rites. The term nyasa means ‘mental appropriation or assignment of the various parts of the body to different deities (which is generally performed at the beginning and end of all the religious rites)”.
Mantras are employed for all sorts of purposes, whether mystical, magical or ritual. The performer holds his right hand successively in front of the mouth, eyes, ears, nostrils, top of the head, forearms, navel and back. The touching of parts of the body is accompanied by recitation of a mantra, a knowledge text, and the prayers that the gods who protect different parts of the body may each take up their special places.
Puja, performed with dhyana, mantra, mudra and nyasa, transforms the person into a deity. A God only can worship a God. A purification of the elements (bhuta shuddhi) and a replacement of the limited self (atman) by that of the deity also takes place. An ‘antryaga’ (inner sacrifice) is performed, whereby the deity is experienced as being present in the performer’s body, and all customary services are imagined and visualized as offered to the deity. There can be up to thirty series of nyasa in a puja.
We notice numerous employments of nyasa. This is also performed on images to install the deities within them. In the upanayana, when the consecrated one is considered pure, he performs nyasa. By means of the matrka, the alphabet or syllables, mother of mantras, the nyasa is performed. The results obtained by the angamantras, i.e., performance of nyasa on parts of the body with special mantras, are discussed in Jayakhya Samhita (Chaps 28-29). Ahirbudhnya Samhita (Chap 37) discusses nyasa in the sense of taking refuge with the God. By means of the nyasa technique, the performer infuses his body with the power inherent in the matrakas, performs mental sacrifices, and offers puja to Ganesha (Malinivijayottara Tantra 8.90).
Yoga and tantric practices are integral parts of the nyasa techniques.