Dynamics of interaction between and currents to mediate double resonances of medial superior olive neurons related to sound localization.

Neurons in the medial superior olive (MSO) exhibit high frequency responses such as subthreshold resonance, which is helpful to sensitively detect a small difference in the arrival time of sounds between two ears for precise sound localization. Recently, except for the high frequency depolarization resonance mediated by a low threshold potassium () current, a low frequency hyperpolarization resonance mediated by a hyperpolarization-activated cation () current is observed in experiments on the MSO neurons, forming double resonances. The complex dynamics underlying double resonances are studied in an MSO neuron model in the present paper. Firstly, double resonances similar to the experimental observations are simulated as the resting membrane potential is between half-activation voltages of and currents, and stimulation current () with large amplitude and exponentially increasing frequency is applied. Secondly, multiple effective factors to modulate double resonances are obtained. Especially, the decrease of time constant of current and increase of conductance of and currents can enhance the depolarization resonance frequency for precise sound localization. Last, different frequency responses of slow and fast currents in formation of the resonances are acquired. A middle phase difference between and currents appears at a high frequency, and the interaction between the positive part of and the negative current forms the depolarization resonance. Interaction between the negative part of and positive current with a middle phase difference results in hyperpolarization resonance at a low frequency. Furthermore, the phase difference between and resonance current can well explain the increase of depolarization resonance frequency modulated by the increase of conductance of or currents. The results present the dynamical and biophysical mechanisms for the double resonances mediated by two currents in the MSO neurons, which is helpful to enhance the depolarization resonance frequency for precise sound localization.