Substrate consciousness and Rigpa

It is about establishing three-dimensional model of the mind. Such models differ between schools. For example, Theravada or Yogacara have many more dimensions to it described.

First dimension is the ordinary mind (psyche), it is equivalent of chitta. It is the dualistic mind responsible for Self-personality grasping. This part is also your base of imagination, rational thinking, intellectualisation. This dimension is switched off when we sleep or are in the coma, or dying.

Second dimension is substrate consciousness that is equivalent of alayavijnana which is storehouse consciousness in Yogacara school, or in Theravada, this corresponds to bhavanga. Storehouse consciousness is essentially your subconsciousness - it always processes information no matter what. It also stores everything, biologically (from your father), and experientially (past actions). Relation with chitta is that chitta allows you to transform and store good or bad seeds back into the storehouse that will one day blossom and re-manifest in psyche again. It is the relative vacuum of consciousness.

Lastly, bare awareness, primordial awareness that is Rigpa. It is equivalent to experiences of Buddha nature or wisdom of Dharmadhatu, or Dharmakaya, also Tathata or even Jhana. Rigpa is based on intuition (jnana as opposed to prajna) coming from touch with suchness. This is seeing things as they are. There are many terms that describe it. For Dzogchen practitioners, the whole singular experience of it is best seen as last remnant after two other layers dissolve at the time of death - the clear light. It is the absolute vacuum of consciousness.

Each one of these layers goes deeper and such is the relation between them, each one emerges from the lower layer. Concepts arise from being in touch with suchness and so on.

Alan Wallace's commentary on Vajra Essence:

For clarification let’s refer to the three-tiered model of the mind presented earlier. The first and most superficial level is the psyche, in which thoughts, fantasies, images, and so forth appear. If you sit quietly and watch your mind, the phenomena you observe manifest in your psyche. We access the second level, the substrate consciousness, in deep sleep, the blackout period of death, and in the practice of shamatha. During shamatha meditation the phenomena observed do not necessarily emanate solely from the psyche, which is encapsulated within this lifetime. Having accessed the substrate consciousness, there is the potential for tapping into memories from past lifetimes, phenomena entangled within a vast network of experiences. These may appear in the form of dreams, visions, desires, or fears whose origin is not to be found in this lifetime. In the case of fear, for example, the anxiety may be very real, yet its origin may be a past-life experience. Such fear is an expression of imprints stored in the substrate consciousness.

Then, having broken through to the third tier of the mind—primordial consciousness—what emerges, the phenomena that appear, are not manifestations of mind and mental processes. From this deeper vantage point, such manifestations and mental processes, which comprise the psyche, are surface phenomena. For the same reason it would also be misleading to depict these primordial experiences as manifestations of the substrate consciousness. Appearances originating in primordial consciousness are the spontaneous, natural effulgence of pristine awareness. Being neither the mind nor mental processes, “these appearances are by nature the play of the manifest space of awareness”—dharmadhatu.

(...)

For example, if you truly fathom the nature of anger as it arises—even something as slight as a mild irritation—it is seen to be nothing other than an expression of pristine awareness. Of course we don’t normally do that. We grasp on to anger, reify it, and then act out within the sphere of the psyche and of ordinary appearances, in which case anger is an afflictive emotion. Therefore, if you fathom the nature of the mental processes—the eight kinds of consciousness—it is seen that they have never been anything other than expressions of primordial consciousness. However, not fathoming their nature, they are then seen either as expressions of the substrate consciousness or expressions of the psyche, indicating that you are locked within samsara.

You can clearly see there is nothing special that cannot be experienced outside Dzogchen and that same experience is also spoken of in Mahayana in great detail.

Rigpa is what in Zen is called "your true self" or "true nature".

In practice of a Zen student, Rigpa manifests as clarity. It's like, when you have spent enough time in the wilderness and got your mind cleared, or you have meditated enough -- and now you have this lucidity. You understand everything that you encounter without much thinking. Things are clear, good-and-bad is clear, and decisions are easy to make -- so no thinking is required. Your actions are direct, precise, and appropriate. That's Rigpa.

It is also what's known in Zen as "first thought, best thought". However, it's not a thought of someone confused and full of fear or lust or aggression or judgement. It is the intuitive spontaneous reaction of a pure mind that is free from confusion.

Sometimes Rigpa is described as one continuous sense of awareness that never sleeps - but this is very misleading! Rigpa is not a watcher, it's not one thing that is always there sitting in the depths. Instead, it is the basic underlying unawareness from which all awareness springs. It's like an alarm clock - you can completely relax and stop watching the time - and it will tell you when it is time to wake up.

In this sense, Rigpa is always with us, and we always use it. It is our most personal sense since the earliest childhood. We seemingly lose touch with it when we are busy with the world of thoughts - but in reality we never lose it. The regular mind becomes aware of Rigpa when we are alone, or are very sick, or in survival mode.

Rigpa is that deep-most sense of sanity that never judges anything and always understands the essence of everything. Rigpa is that level of mind that understands without words, which you sometimes have to do in order to communicate its vision, which can hardly ever be adequately expressed.

Rigpa is the mind of Enlightenment.