As a rule the only mantra used in this sadhana is that of the Mother or of my name and the Mother. The concentration in the heart and the concentration in the head can both be used — each has its own result. The first opens up the psychic being and brings bhakti, love and union with the Mother, her presence within the heart and the action of her Force in the nature. The other opens the mind to self-realisation, to the consciousness of what is above mind, to the ascent of the consciousness out of the body and the descent of the higher consciousness into the body.
Ref: Letters on Himself and The Ashram