Alan Lightman – Dance for Two (1996)
…Eventually, a large fraction of the trillion neurons in the man’s brain become involved with computing the visual and auditory data just acquired. Sodium and potassium gates open and close. Electrical currents speed along neuron fibers. Molecules flow from one nerve ending to the next.
All of this is known. What is not known is why, after about a minute, the man walks over to the woman and smiles.