The plane on which one can possess physical consciousness is the gross world. The planes on which one can possess consciousness of desires are in the subtle world, and the planes on which the soul can have mental consciousness are in the mental world. The source of desire is to be found in the mind, which is on the mental planes. Here the seed of desire is attached to the mind; the desire exists here in a latent form, in the same way as the tree is latent in the seed. The mental body, which is the seat of the mind, is often called karan sharir, or the causal body, because it stores within itself the seeds or the causes of all desires. The mind retains all impressions and dispositions in a latent form. The limited “I,” or ego, is composed of these sanskaras. However, the actual manifestation of sanskaras in consciousness, as expressed through different mental processes, takes place in the subtle body.
-Discourses 7th Ed., p327