sarva-dvārāṇi sanyamya mano hṛidi nirudhya cha
mūrdhnyādhāyātmanaḥ prāṇam āsthito yoga-dhāraṇām||12|| 

Meaning : Having controlled all the gates of the body (senses), and restrained the mind in the heart, placing the life-force (prāṇa) at the top of the head, one becomes firmly established in yogic concentration.