Vijnanamaya means composed of vijnana, or intellect, the faculty which discriminates, determines or wills. It is the sheath composed of more intellection, associated with the organs of perception. This knowledge sheath cannot be the supreme self for the following reasons; It is subject to change, It is insentient, It is a limited thing, It is not constantly present.
A large part of this Kosh is in the realm, of the unconscious and is a major repository of information. The feeling of ‘me’ and ‘mine’, and the faculty of intelligence and reasoning constitute the fourth or Vigyanmaya Kosh.The feeling of freshness that ‘I had had a deep sleep’ is said to arise from this Kosh. When one closes the eyes and relaxes during meditation, the functioning of the Manomaya Kosh becomes minimum. The Vigyanmaya Kosh comes in the front and gets active. In the final stages of meditation, the intellect becomes stable and mind becomes still and this is called Samadhi.
Meditation when used as a therapeutic tool works in the Vigyanmaya Kosh. All sorts of reasoning and counselling (psycho-therapy) also act on this Kosh