Traditional yogic disciplines advise the seeker to concentrate between the eyebrows, chanting OM and focusing on the Divine Will. Sri Aurobindo notes this practice, and develops it to provide access to the higher ranges of consciousness above the mental level. The Isha Upanishad notes that there is a “lid” that is brilliant and golden in color that prevents the seeker from seeing the Truth of existence. That lid is the border between the mental and the higher planes. The seeker, through the concentration in the mental centre, can bring about a receptive silent state of the mentality, by which the aspiration and will can open to the higher planes and become receptive to the descent of the states of awareness that are active at those levels.
Sri Aurobindo observes: “That other way is the concentration in the head, in the mental centre. This, if it brings about the silence of the surface mind, opens up an inner, larger, deeper mind within which is more capable of receiving spiritual experience and spiritual knowledge. But once concentrated here one must open the silent mental consciousness upward to all that is above mind. After a time one feels the consciousness rising upward and in the end it rises beyond the lid which has so long kept it tied in the body and finds a centre above the head where it is liberated into the Infinite. There it begins to come into contact with the universal Self, the Divine Peace, Light, Power, Knowledge, Bliss, to enter into that and become that, to feel the descent of these things into the nature. To concentrate in the head with the aspiration for quietude in the mind and the realisation of the Self and Divine above is the second way of concentration. It is important, however, to remember that the concentration of the consciousness in the head is only a preparation for its rising to the centre above; otherwise, one may get shut up in one’s own mind and its experiences or at best attain only to a reflection of the Truth above instead of rising into the spiritual transcendence to live there. For some the mental concentration is easier, for some the concentration in the heart centre; some are capable of doing both alternately — but to begin with the heart centre, if one can do it, is the more desirable.”
Sri Aurobindo, Integral Yoga: Sri Aurobindo’s Teaching and Method of Practice, Chapter 6, Sadhana Through Work, Meditation and Love and Devotion, Meditation and Concentration in the Integral Yoga, pp. 149-153