It is important to understand the difference between Natya - Nrttya and Nrtta. The first two terms refer to theatrical performance while Nrtta is defined in the Abhinaya Darpana of Nandikesvara as ‘that dance devoid of any type of emotional mood’.
This corresponds exactly to the explanation of Abhava yoga given by Mahesvara (Lord Siva) in the eleventh chapter of the Kurma Purana. This states that Abhava Yoga is that yoga in which one contemplates oneself as void and without any shadow (manifestation) of anything, which therefore enables one to visualize the Self. Here, Abhava refers to a state free from any emotional support, also exemplified in Nrtta as defined by Nandikesvara.
The eleventh chapter of the Kurma Purana includes a detailed explanation of Pashupata Yoga. Nrtta formed a large part of the corrective Sadhana of the Pashupata yogins. This is clearly indicated in the eighth sutra of the first chapter of the Pashupata Sutras.
Out of the one hundred and eight karanas mentioned in the Natya Shastra, not more than thirty-six karanas are used for the purpose of self cultivation.
Most of the asanas used in contemporary Hatha Yoga schools are adaptations of the standing and squatting karanas. The important difference is that in the original practice the placement of the legs was achieved through the cultivation of the inherent energy of the legs whereas nowadays the legs are manipulated with the hands to achieve the same external shapes. Five of the karanas are responsible for restoring the body’s natural energetic responsiveness required for this authentic practice.
Nrtta is that Sadhana through which the sadhaka (aspirant) rediscovers the rhythmic life currents hidden in the body’s folds and limbs by means of unimposed natural positioning.
The three forms of Nrtta are: Ashta Matrikas (the eight mother palms), Lasya (Kali's creative dance) and Ananda (Samhara) Tandava (Shiva's destructive dance).