Pulse-coupled neuron models as investigative tools for musical consonance

We investigate the mode locking properties of simple dynamical models of pulse-coupled neurons to two tones, i.e., simple musical intervals. A recently proposed nonlinear synchronization theory of musical consonance links the subjective ranking from consonant to dissonant intervals to the universal ordering of robustness of mode locking ratios in forced nonlinear oscillators. The theory was illustrated using two leaky integrate-and-fire neuron models with mutual excitatory coupling, with each neuron firing at one of the two frequencies in the musical interval. We show that the ordering of mode locked states in such models is not universal, but depends on coupling strength. Further, unless the coupling is weak, the observed ratio of firing frequencies is higher than that of the input tones. We finally explore generic aspects of a possible synchronization theory by driving the model neurons with sinusoidal forcing, leading to down-converted, more realistic firing rates. This model exhibits one-to-one entrainment when the input frequencies are in simple ratios. We also consider the robustness to the presence of noise that is present in the neural firing activity. We briefly discuss agreements and discrepancies between predictions from this theory and physiological/psychophysical data, and suggest directions in which to develop this theory further.