BG Chap 13 - The way the soul functions in the body
Just as one sun illuminates the whole world with its light, the soul illuminates the whole body by its consciousness. As a flame pervades a room by its rays, the soul pervades the whole body by its quality. As the sun is situated in one place but is illuminating the whole universe, so a small particle of spirit soul, although situated in the heart of this body, is illuminating the whole body by consciousness. Thus consciousness is the proof of the presence of the soul, as sunshine or light is the proof of the presence of the sun. When the soul is present in the body, there is consciousness all over the body, and as soon as the soul has passed from the body there is no more consciousness.