Who is behind the functioning of our 5 senses ?

“Brahman that is immediate and direct —the Self that is within all.” “You cannot see That which is the Seer of seeing;
you cannot hear That which is the Hearer of hearing;
you cannot think of That which is the Thinker of thought;
you cannot know That which is the Knower of knowledge.
This is your Self, that is within all; everything else but This is perishable.”

— (Br. Up. 3.4.2)