The key is to understand the relationship between hadaya vatthu and the brain.
The following are the key points:
1. Citta and thoughts (or consciousness) arise in hadaya vatthu.
2. But all six signals from the external world (sights through dhammā) come in via the brain.
3. While being unconscious the brain is totally inactive. Even while in deep sleep it is mostly inactive.
– For citta to arise in hadaya vatthu, there must be an arammana coming through one of the six senses.
– Thus, if the brain is not active, no citta vithi can be triggered, and thus no consciousness.
4. However, the gandhabba (hadaya vatthu plus pasada rupa) is alive at all times. But no citta vithi can arise until the hadaya vatthu is triggered.
5. Each citta has AT LEAST the seven universal cetasika: Phassa (contact); vēdanā (feeling); saññā (perception); cētanā (volition); Ekaggata (One-pointedness); jivitindriya (life faculty); manasikāra (memory).
– However, normally other cetasika also arise. There are 52 cetasika including vedana and saññā, and any citta with cetasika has saṅkhāra. Since “mano saṅkhāra” are defined as “vedana and saññā”
saṅkhāra are ALWAYS in a citta.
6. See, “Cetasika (Mental Factors)” for details on cetaiska.
7. Further details on the role of the brain at; “Brain – Interface between Mind and Body”
If not clear, please feel to ask questions.