The reference to the 'cave of the Heart' has several interpretations. However, in simple terms, in some ancient yogic schools the 'cave of the Heart' is called the 'seat of the soul' in the body. This has precedent in the Upanishads and the Bhagavad-Gita. Teacher anadi dissects this cave into several layers: personal, psychic or energetic, and spiritual, i.e., the soul, and deeper still, the 'beloved' or the 'creator.' [The Hindus might say Atman and Paramatman]. St. Augustine called it imtima mea, the 'inward dwelling,' a 'shared bedroom,' a 'closet of intimacy,' an 'abyss,' and asked, "whose heart is seen into?" However, there is also reference made, in the Vivekachudamani of Sankara, to the 'cave of the intellect, buddhi,' or buddhi guha, and also guha hitam, or 'the secret abode of the infinite'. There appears to be a close connection between these two caves. In Kaballah they mention the mothering, discriminative intelligence of the heart (Binah). Sri Atmananda Krishna Menon said that 'the head and the heart are not water-tight compartments.' Even modern research suggests that the heart has its own nervous system, is an organ of perception and memory, and is in close communication with the brain. (1) In ancient Egypt the god Ptah created the world from the 'imagination of his heart,' [similar to PB's 'presence of the World-Mind in the heart'] and Islamic philosopher Ibn Arabi also taught that to imagine is an ability of the heart.
So we must then also think somewhat 'imaginatively' when considering this mysterious topic. Buddhi, in Samkhya terminology, is similar to the yogic vijnanamaya kosha, or the intellectual sheath. Some say that here in the cave of buddhi is where one finds the Atman, others say that Brahman is found there ( "buddhau guha yam brahmasti"). Advaitists generally consider them both to be pure consciousness, so when Atman is realised, Brahman is also. The Upanishads say 'knowledge of Brahman is the same as 'becoming Brahman' (brahmavid brahmaive bhavati) whereas Sankara said that 'knowledge of Brahman' leads to the 'experience of Brahman' (anubhava avasanamn brahma vignanam ). We will not argue yes or no on these points. Sankara, the great jnani (as well as bhakta and tantrist), in his Vivekachudamani, wrote:
"In the cave of the intellect is the Brahman, which is neither existent nor non-existent, the transcendental non-dual Truth. One who dwells in this cave, becoming one with the Truth, for him there is no more entry into the bodily cave," (2)
The process of finding the Brahman for Sankara and the advaitists is an epistemological one, where the five sheaths are analyzed to extract the Truth; it is often mistakenly understood to be an ontological 'peeling of the onion' to find the Self essence underlying them. But the non-dual Truth includes the sheaths and is not an 'essence' underlying or deep within them. Such is more often the yogic interpretation of the five sheath doctrine. Sankara didn't mean the methodology of 'neti, neti' ('not this, not this') to be taken ontologically, that is, as negating the not-Self, but only as an epistemological exercise in order to affirm by investigation what is the Self. This is how it was presented in the Tittireya Upanishad, one of the sources for Sankara's teaching. Each succeeding level of investigation includes the previous one, until none are seen as other than the blissful nature of the self. There are no references in this Upanishad that consider them in any way as ‘not real.’ The vision is wholistic, not eclusive.
Ramana Maharshi, modern master of the Heart, would frequently quote scripture saying that 'the Self is always shining in the intellectual sheath.' In Samkhya philosophy, generally adopted by the yoga schools, buddhi being the closest upadhi, or 'limiting adjunct,' to Atman, is the filter of the light of the Atman to the mind and senses. Buddhi creates the 'I'-thought or ego, and the 'luminous reason' (susksma buddhi) is the means to enlightenment, while the undeveloped buddhi is the proximate cause of our ignorance and identification with the ego-I. When we do not know ourself as Atman, we mistake ourself to be the 'shining ego in the buddhi.' The shining nature of buddhi, being easily mistaken for the light of the Atman, means that only discriminating knowledge can get us out of this predicament. This means, strangely enough, that the buddhi must discriminate itself out of existence, in a manner of speaking, to get out of its own way. When the 'buddhi gets enlightened, Self-realisation takes place,' according to Swami Ranaganathananda. anadi calls this the second level of enlightenment: awakening not only to the experience, but to the understanding of the experience as well. And further, out of the meeting of intelligence and sensitivity, which produces the understanding, comes the fruit of the understanding, which is the appreciation of the experience. The heart is involved. This is an added dimension over and above the experience itself.
Now, here's where the Advaitic reasoning gets a little confusing. We won't try to solve the problem of how the ever-free Self or Atman becomes deluded by its very own adjuncts or bodies (koshas), etc., that is too great a task at this point.
While the Upanishad considers the Buddhi to be closest to Atman, in between Buddhi and Atman lies undifferentiated Maya. In yoga they sometimes refer to this - in the microcosm - as the anandamaya kosha or bliss sheath. This is equated by Swami Ranganathananda with the causal body, also in the heart, and which is active in deep sleep. During sleep, the vignanamaya kosha, the sheath of knowledge or intellect, lies dormant in seed-form, and there is thus no knowing possible. The bliss sheath is active, yet being of the nature of maya, the undifferentiated, is veiled by tamas, and one has no actual direct experience of bliss while sleeping. One can only infer such a quality upon awakening by saying, 'I slept soundly,' etc. The Mandukya Upanishad says that Turiya is what recognizes the state of deep sleep, but only when we are in the waking state. This point is debated: some say there is no awareness during ordinary deep sleep, while others say that Mind or the Self is always aware; this is similar to the dilemma faced in the Tibetan tradition with the dawning of the 'emptiness-luminosity' at the point of death, everyone experiences it, but most pass into unconsciousness almost immediately]. Some contemporary teachers of 'consciousness' say we are actually aware of the experience or quality of sleep, while we are sleeping, but is this reasonable? Are we, prior to enlightenment, aware of anything during sleep, or are we essentially deconstructed in the absolute unconsciousness?
In other yoga schools, they equate the causal body with the 'bliss sheath in the heart.' Swami Yogeshwaranand Saraswati writes:
"A stream of rays pertaining to the life-force arises from the bliss sheath (the causal body in the heart) and goes to the astral body (manomaya and vijnanamaya koshas in the brain) and from there to the physical body." (3)
Ramana said it was the Heart itself whose light went upwards to the head and then into the bodily centers below. He spoke of the light of the moon (sahasrar) being the borrowed light of the sun (the Heart).
Yet, as mentioned, in the bliss sheath the intellectual sheath lies dormant during sleep. Even though the bliss sheath is the closest to Atman, it has no way of reflecting the intelligence and inherent self-shining nature of the Atman . Only the intellectual sheath, the vijnanamaya kosha , or Buddhi, can do so, and it can do so only in the waking state. The bliss sheath, being the causal body of the soul and of the nature of the primal Undifferentiated, is characterised, paradoxically, by 'darkness and vacuity,' inasmuch as it is covered by the veiling power of tamas. The so-called bliss sheath is so fine, like a delicate silken covering, that it is said to be almost an integral part of the soul.
Since the bliss-sheath is embedded in the other sheaths, in waking life one can have positive experiences that give one a feeling of bliss. But there is no 'knowing' in the human body without the vijnanamaya kosha.
The 17th century Hindu saint, Sri Samartha Ramadas, in his treatise on gnana yoga, Atmaram, said, "The bliss-attainment of a yogi is maya." (quoted in The Notebooks of Paul Brunton) This makes sense inasmuch as the bliss sheath is an initial product of maya itself. The bliss is really from the Soul, but the jivatman (vijnana-maya-atman, or the jiva in the intellectual sheath) co-opts it for itself.
Now here I am stepping beyond the limits of my theoretical knowledge, but will try to explain to the best of my understanding.
In Sant Mat, where they mystically try to peal off these sheaths one by one by merging with the creative logos in the form of the luminous sound current that permeates all creation, they finally reach a stage where the Soul has shed the physical, astral, causal (in their school the manomaya kosha or manas) and the super-causal body (vijnanamaya kosha) and is now only vested with the extremely fine anadamaya kosha or bliss sheath. However, the soul is now macrocosmically also in a region known as Maha Sunn, a void which separates the created from the Uncreated worlds, and which is said to be characterized by dense darkness which the Soul cannot penetrate without the help of the Satguru, whose roots are in Sat, or the realms of Truth. The soul at this stage has shed mind, ego, and intellect, and can do no more for herself. This dense darkness of Maha Sunn (which even saint Kabir mentioned) seems to correspond with the "darkness and vacuity" of the causal body or bliss sheath mentioned by Ranganathananda.
For the saints, the 'heart-lotus' in the body is at 'the seat of the soul' between the two eyebrows, not in the heart center. [This is also the focus of attention in the waking state; in dreams attention is said to go down to the throat, and in deep sleep to the navel]. Even so, Sant Kirpal Singh would sometimes point to his chest and say, "the Master reside here." This same double reference is found in the Gita where Krishna says "I am the Heart in all Beings," but the yogi is also to meditate "with the mind in the heart, and the life-force in the head, established in concentration through yoga." He is encouraged to die that way, too. The same is held in Tibetan Buddhism where the yogi is exhorted to go out through the crown of the head.
The only way I can reconcile these apparently different positions is by taking a non-spatial, non-bodily oriented point of view of the highest realisation in these particular paths. Then the awakening at the heart and the third eye would only indicate separate awakenings within the total I Am. But I'm not sure they would all agree with this assessment.
All schools, whatever the tradition, are in agreement that the human form in the waking state is the precious circumstance where enlightenment can occur. As Christ said, "work while it is day, and not at night, when no man can work." Or one can just assume there is no-doer, and take his chances.
1. Stephen Harrod Bruhner, The Secret Teachings of Plants: The Intelligence of the Heart in the Direct Perception of Nature (Rochester, Vermont: Bear & Company, 2004), p. 71, 81-87
2. Vivekachudamani, verse 266
3. Yogesh Satyeswaranand Saraswati, Science of Soul (New Delhi, India: Yoga Niketan Trust, 1987), p. 238