In 2001, brain imaging showed McGill University researchers Anne Blood and Robert Zatorre that subjects listening to a C–G perfect fifth directed the signal to a “reward system,” experiencing a “smooth, sweet” sound. When the same subjects heard a C/C-sharp dissonance, the signal was instead directed to the “fight-or-flight” areas of the brain’s limbic system. Dissonant chords were characterized as having a “rough” sound.6
