A theoretical model of neurons associated with hearing may explain why certain note combinations are more pleasing than others. New research supports the theory by quantifying the effect.
The most pleasing musical chords have simple mathematical relationships between the different sound frequencies within them, but the source of this perception is mysterious. A recent mathematical model suggests that the key may be the rhythmically consistent firing of neurons in response to a harmonious pair of frequencies. Now the researchers who developed the model report 2 September in Physical Review Letters  that they have quantified the effect by calculating the information content of their model’s neural signals and showed that it increases for tone pairs that are more pleasant sounding. The model may also provide insights into other sensations besides hearing.
Going back to Pythagoras in 500 BCE, people have noticed that pairs of notes with simple frequency ratios, such as tones separated by an octave (2:1) or a perfect fifth (3:2), produce a more tranquil sound than, say, a minor second (16:15). Hearing the difference doesn’t require musical training, as even infants and animals respond to it. Recent research suggests that the sensation of harmony, or “consonance,” is not simply the result of the way sound waves combine; it arises from the processing of sound into electrical signals. “The behavioral preference of consonant chords is due to some basic principles of neural functionality,” says Bernardo Spagnolo of the University of Palermo in Italy.
For more, please see Sweet Music to Your Nerves, Published September 2, 2011 | Phys. Rev. Focus 28, 9 (2011) | DOI: 10.1103/PhysRevFocus.28.9
 Yu. V. Ushakov, and A. A. Dubkov, Regularity of Spike Trains and Harmony Perception in a Model of the Auditory System, Phys. Rev. Lett. 107, 108103 (2011).