Music communicates to us emotionally through systematic violations of expectations.  These violations can occur in any domain—the domain of pitch, timbre, contour, rhythm, tempo, and so on—but occur them must.  Music is organized sound, but the organization has to involve some element of the unexpected or it is emotionally flat and robotic.  Too much organization may technically still be music, but it would be music that no one wants to listen to.

Effective music—groove—involves subtle violations of timing.  We know through culture and experience that music is not threatening, and our cognitive system interprets these violations as a source of pleasure and amusement.  This emotional response to groove occurs via the [reptilian brain and limbic system] rather than via [the cerebral cortex].  Our response to groove is largely pre- or unconscious because it goes through the cerebellum rather than the frontal lobes.  What is remarkable is that all these different pathways integrate into aour experience of a single song.