Non-calyceal inputs gate the timing of calyx of Held evoked MNTB output

Synaptic filtering by short-term plasticity (STP) influences the strength and timing of the input-output function of neurons during ongoing activity. In the medial nucleus of the trapezoid body (MNTB), an ultrafast sign-inverting relay, short-term depression (STD) of the dominant calyx of Held inputs affects the exquisite output timing of these neurons and thereby influences sound processing relevant for sound source localization. We find that additional excitatory non-calyceal inputs, targeting soma and dendrites of MNTB neurons, show prominent frequency-dependent facilitation and asynchronous release leading to a steady depolarizing conductance. The integration of non-calyceal and the calyx of Held input provides a mechanism for adjusting the temporal precision and faithfulness of output during prolonged high-frequency activity in a range relevant for auditory processing. Thus, non-calyceal inputs tune suprathreshold output generation in a functionally relevant manner, qualified to set the neuronal representation of sound sources in space.