The subtle body is composed of the vital sheath (prānamaya kośa), mental sheath (manomaya kośa), and sheath of the intellect (vijñānamaya kośa). The vital sheath is the life force that operates the autonomic nervous system, thus controlling respiration (prāna), excretion (apāna), and digestion (samāna), and also various functions of the cerebro-spinal system such as exertion (vyāna) and growth. The vital sheath, moreover, mediates the soul’s departure from the body at the time of death (udāna). The manomaya kośa comprises the volitional, or deliberative mind, as well as the five organs of perception; whereas the vijñānamaya kośa (Buddhism’s) is the cognitive or determinative mind, along with the five organs of perception.
Through the buddhi, or cognitive mind, all other faculties of the mind, whether volitional or emotional, receive their light. However, as already mentioned, the buddhi simply permits the passage of the light of the witness-self (sāksin) and thus appears to be self-luminous. Vedanta claims that though the buddhi is located in the heart within a tiny space (ākāśa) ‘about the size of a thumb’, the witness-self dwells even deeper within our being, within the buddhi itself. Therefore, the buddhi—only one step away from the witness-self—is still identified with the non-Self and asserts itself as the knower and the doer within the mental and vital sheaths, and functions as the empirical self that reincarnates.
Human cognition exemplifies how the various mental faculties function together within the mental and intelligence sheaths. According to Vedanta, cognition is a fourfold operation. First, the deliberative faculty of the mind (manas) asks: ‘What is this object?’ The memory (citta) attempts to recall similar objects. Then, the determinative faculty (buddhi) is able to ascertain: ‘It is a desk.’ Finally, the sense of egoism (ahamkāra) makes the association: ‘I am sitting at the desk.’ Throughout the cognitive process, however—whether we know it or not—the light of the Self, shining through the buddhi to the organs of perception, reveals everything that we experience. William M Indich, in his book Consciousness in Advaita Vedanta, explains: ‘In visual perception, then, Brahman intelligence reflected in mind is extended out along the medium of the organ of vision, which Advaitins claim is the nature of light (teas) … contacts an object, assumes its form, and reveals it as known.’
This Upanishadic model of the fivefold sheath maintains that consciousness does not originate in the brain—nor even in the mind, for that matter, because the mind merely passes on the light of consciousness. The brain, the mind, and the body are merely physical mediums for the expression of consciousness. Moreover, the Yoga-Vedanta system of psychology asserts that thought, which is a specific type of consciousness, is a function of the mind, not the brain. ‘In the Vedantic view the mind is not a process;’ Swami Satprakashananda summarizes, ‘nor is it a function, or a state, or an attribute of something else. It is a positive substance, though not ultimately real. It has definite functions and states. It is one of the products of primordial nature, the potential cause of the universe, called prakrti or māyā, which has no consciousness inherent in it’ .
Yoga-Vedanta uphold the premise that one’s own consciousness—disciplined and refined through the path of yoga—is the clearest and most reliable lens for perceiving and grasping the nature of human and transcendental consciousness. For thousands of years mind and consciousness have been primary subjects of introspective investigation. Consequently, the rsis were able to develop sophisticated techniques for tracing the origin and nature of consciousness, which have been handed down from guru to disciple to the present day.