This is edited from letters I wrote 20 years ago on heart base.
A friend wrote to me that the reason they can’t believe in the Atthakatta (commentaries) is because they say the heart is the base for consciousness. they wrote:
O n the other hand, Buddaghosa CONFIRMS in Visuddimagga that the seat of the Mind is Heart. Now we know, this cannot be possible, through lots of knowledge we have gained on the functions of the heart and the brain and the associated central nervous system. If the heart is the seat of the consciousness, what happens during open heart surgeries where the heart is kept inactive for hours before activating by an electric shock at the end of the operation.
On the other hand, what consciousness a person will have who receives a new heart from another dead person?
Robert: All of us are much conditioned by an age where scientific discoveries seem so testable and provable. It is natural that doubts arise on this matter. The Visuddhimagga (viii, 111)says about hadaya-vatthu (heart basis): they describe the heart and then note that inside the heart “there is hollow the size of a punnaga seeds bed where half a pastata measure of blood is kept, with which as their support the mind element and mind-consciousness element occur.” Note that it is not the heart itself that is the hadaya-vatthu NOR is it the blood inside the heart but rather as the Paramatthamanjusa (see vis.xiii note 5 ) says “the heart basis occurs with this blood as its support”. You see the actual hadaya-vatthu is incredibly sublime – in scientific measure it wouldn’t even amount to a tiny fraction of a gram. It might even be so refined as to be unmeasurable by scientific instruments.
This applies also to the other sense organs (pasada rupa). The Atthasalini remarks that the very purpose of using the term pasada is to dismiss the popular misconception of what we think an eye or an ear is. (see karunadasa p45)The actual sensitive matter in the eye and ear is very refined. If someone dies then the ear-sense and eye sense (sotapasada and cakkhu-pasada ) are immediately no longer produced (they are produced by kamma only) yet one would not notice much outward change looking at the eye and ear(at least for the first few minutes before decomposition sets in). The same applies to the heart – the blood in the heart would have the same volume after death and yet the hadaya-vatthu is no longer present.
I think you accept that consciousness arises soon after conception. The fetus at that stage is so tiny as to be invisible to all but the most trained eye (if even that large). yet consciousness is arising and passing away dependent on some matter(rupa) somewhere. There is certainly no brain yet but according to the commentaries the heart basis (hadaya-vattu ) ,that extremely subtle rupa, is already present – conditioned by kamma. This shows how extraordinarily subtle this type of rupa is. There is more that I could write about this. However, I think one can see how heart transplants etc. make no difference to the arising and passing of this subtle conditioned rupa.
What does the brain do then? It does something, it is like wiring center needed for functioning of the body mind – Sure if you pull out a few wires , just as with a computer, things aren’t going to work so well. No doubt someone ignorant of the chip in a computer could play around with the mass of wirings and see how the computer stopped working or had some misfunction- they might think, wow so that is ‘brain’ of the computer . Not knowing that the tiny chip is really where the processing is done.