Apologies I cannot provide a reference off the top of my head, but the Buddha said that mentality required a physical basis. Commentators interpreted this as advocating the prevailing Indian cardiac theory that the heart was the physical seat of consciousness, although the Buddha did not explicitly call out any proximite location.
That said, to your question of what "exists", I'd caution against unwittingly leaping to an ontological interpretation. To use an analogy...
For the man watching television but hearing no sound... it could be because the volume is off, or it could be because he is deaf. In his world (loka)
, no TV sound "exists"... but whether the physical reason for this is attributable to deafness (no audible vibrations being detected) or the volume being turned down (no audible vibrations being produced), is inconsequential in terms of the resultant first-hand present-moment experience of seeing but not hearing the television.
Compare that to when matter could be said to "exist" or otherwise.