The approach was focused on presymbolic processing -- and tried to optimize harmony. Harmony was, interestingly, the first mathematical model of the mind (by Pythagoreans/platonists in ancient Greece). It has a lot going for it these days, too, to understand oscillatory coupling in neural circuits. I learned recently that brain waves are harmonics (frequency doublings), which somehow I missed before!
Consonance results in greater periodicity, meaning that the action potentials are more likely to line up, whereas dissonance has less periodicity, so action potentials don't line up. It feels better (there is pleasure) when the action potentials align because of hebbian reinforcement (synchronous firing). This assumes that reinforcement would be pleasurable, but pleasure is the main reinforcer at a cognitive level.