The arrival times of a sound at the two ears are only microseconds apart, but both birds and mammals can use these interaural time differences to localize low-frequency sounds. Traditionally, it was thought that the underlying mechanism involved only coincidence detection of excitatory inputs from the two ears. However, recent findings have uncovered profound roles for synaptic inhibition in the processing of interaural time differences. In mammals, exquisitely timed hyperpolarizing inhibition adjusts the temporal sensitivity of coincidence detector neurons to the physiologically relevant range of interaural time differences. Inhibition onto bird coincidence detectors, by contrast, is depolarizing and devoid of temporal information, providing a mechanism for gain control.
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