Sri Aurobindo describes two main areas of concentration within the being, the heart centre and the head. For most people, the concentration in the heart centre turns out to be the safest and easiest to achieve realisation. Yoga, to be effective, must move beyond either a purely mental exercise or emotional activity. Concentration can be an aid in this process.
As one develops the witness consciousness, the concentration can actually continue while one is engaged in activities in the outer life. The inner witness maintains the aspiration, while the outer nature carries out its functions under the observation of the witness. The surface mind, the surface heart, the surface vital being, the surface physical entity will continue to act and focus on the needs of that action, while the inner witness maintains the link to the Divine Presence and keeps the inward concentration alive.
Sri Aurobindo writes: “You have asked what is the discipline to be followed in order to convert the mental seeking into a living spiritual experience. The first necessity is the practice of concentration of your consciousness within yourself. The ordinary human mind has an activity on the surface which veils the real Self. But there is another, a hidden consciousness within behind the surface one in which we can become aware of the real Self and of a larger deeper truth of nature, can realise the Self and liberate and transform the nature. To quiet the surface mind and begin to live within is the object of this concentration. Of this true consciousness other than the superficial there are two main centres, one in the heart (not the physical heart, but the cardiac centre in the middle of the chest), one in the head. The concentration in the heart opens within and by following this inward opening and going deep one becomes aware of the soul or psychic being, the divine element in the individual. This being unveiled begins to come forward, to govern the nature, to turn it and all its movements towards the Truth, towards the Divine, and to call down into it all that is above. It brings the consciousness of the Presence, the dedication of the being to the Highest and invites the descent into our nature of a greater Force and Consciousness which is waiting above us. To concentrate in the heart centre with the offering of oneself to the Divine and the aspiration for this inward opening and for the Presence in the heart is the first way and, if it can be done, the natural beginning; for its result once obtained makes the spiritual path far more easy and safe than if one begins the other way.”
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